[{"file":[{"date_created":"2026-06-19T09:45:21Z","date_updated":"2026-06-19T09:45:21Z","content_type":"application/pdf","access_level":"open_access","creator":"dernst","checksum":"66949af6e620c8ef37de42688829a3e3","file_name":"2026_AstrophysicalJourLetters_Chisholm.pdf","file_size":919919,"success":1,"file_id":"22098","relation":"main_file"}],"acknowledgement":"We thank the referees for detailed and highly constructive reports that significantly improved the scope and breadth of the manuscript. J.C. thanks Hollis Akins, Volker Bromm, Rui Chaves-Marques, Steve Finkelstein, Karl Gebhardt, Keith Hawkins, Harley Katz, Stellar Offner, Daniel Schaerer, Grace Telford, and Jorick Vink for conversations that improved the Letter. A.d.G. acknowledges support from a Clay Fellowship awarded by the Smithsonian Astrophysical Observatory. M.B.K. acknowledges support from NSF grants AST-2108962 and AST-2408247; NASA grant 80NSSC22K0827; HST-GO-16686, HST-AR-17028, JWST-GO-03788, and JWST-AR-06278 from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555; and from the Samuel T. and Fern Yanagisawa Regents Professorship in Astronomy at UT Austin. A.A.C.S. acknowledges support by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) in the form of an Emmy Noether Research Group—Project-ID 445674056 (SA4064/1-1, PI Sander). A.A.C.S. further acknowledges support from the Deutsches Zentrum für Luft und Raumfahrt (DLR) grant grants 50 OR 2509 (PI: A.A.C. Sander) and 50 OR 2306 (PI: V. Ramachandran/A.A.C. Sander) as well as from the Federal Ministry of Research, Technology, and Space (BMFTR) and the Baden-Württemberg Ministry of Science as part of the Excellence Strategy of the German Federal and State Governments. This project was cofunded by the European Union (Project 101183150—OCEANS).\r\n\r\nThis work is based in part on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These observations are associated with programs 1180, 1181, 1208, 1212, 1213, 1215, 1286, 1345, 1433, 2198, 2561, 2750, 2767, 4106, 4233, 5105, 5224, 6368, and 6585.","doi":"10.3847/2041-8213/ae6dae","article_processing_charge":"Yes","quality_controlled":"1","article_type":"original","abstract":[{"lang":"eng","text":"Little Red Dots (LRDs), among the most enigmatic high-redshift discoveries by JWST, are commonly believed to be powered by accreting supermassive black holes. Here, we explore the possibility that these sources are globular clusters in formation, with rest-frame UV arising from a very young stellar population and rest-frame optical from a short-lived supermassive (>104 M⊙) star. The spectral profiles of LRDs are broadly consistent with this scenario, though the observed temperatures and bolometric luminosities favor emission reprocessed by optically thick continuum-driven winds not fully captured by current models. The LRD z ∼ 5−7 UV luminosity function naturally evolves, under standard evolutionary and mass-loss prescriptions, into a present-day mass function with a turnover at log10(M*/M⊙) = 5.3 and an exponential cutoff at high masses, consistent with local globular cluster populations. We estimate the total present-day number density of LRDs formed across all redshifts to be ≈0.3 Mpc−3, similar within uncertainties to local globular clusters. The observed LRD redshift range matches the age distribution of metal-poor globular clusters, without current LRD counterparts to the metal-rich population. If LRDs are globular clusters in formation, we predict chemical abundance patterns characteristic of multiple stellar populations, including enhanced He and N, and potential Na–O and Al–Mg anticorrelations. These results offer a local perspective to explore this surprisingly abundant population of distant sources, and a potential new window into extreme stellar astrophysics in the early Universe."}],"publication":"The Astrophysical Journal Letters","scopus_import":"1","publisher":"IOP Publishing","tmp":{"name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","image":"/images/cc_by.png","short":"CC BY (4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode"},"DOAJ_listed":"1","license":"https://creativecommons.org/licenses/by/4.0/","type":"journal_article","fulldoi":"https://doi.org/10.3847/2041-8213/ae6dae","volume":1004,"article_number":"L4","oa_version":"Published Version","publication_status":"published","status":"public","department":[{"_id":"JoMa"}],"year":"2026","OA_type":"gold","citation":{"ista":"Chisholm J, Berg DA, Boylan-Kolchin M, De Graaff A, Furtak LJ, Kokorev V, Matthee JJ, Muñoz JB, Naidu RP, Sander AAC. 2026. Little Red Dots as globular clusters in formation. The Astrophysical Journal Letters. 1004(1), L4.","chicago":"Chisholm, John, Danielle A. Berg, Michael Boylan-Kolchin, Anna De Graaff, Lukas J. Furtak, Vasily Kokorev, Jorryt J Matthee, Julian B. Muñoz, Rohan P. Naidu, and Andreas A.C. Sander. “Little Red Dots as Globular Clusters in Formation.” <i>The Astrophysical Journal Letters</i>. IOP Publishing, 2026. <a href=\"https://doi.org/10.3847/2041-8213/ae6dae\">https://doi.org/10.3847/2041-8213/ae6dae</a>.","ieee":"J. Chisholm <i>et al.</i>, “Little Red Dots as globular clusters in formation,” <i>The Astrophysical Journal Letters</i>, vol. 1004, no. 1. IOP Publishing, 2026.","mla":"Chisholm, John, et al. “Little Red Dots as Globular Clusters in Formation.” <i>The Astrophysical Journal Letters</i>, vol. 1004, no. 1, L4, IOP Publishing, 2026, doi:<a href=\"https://doi.org/10.3847/2041-8213/ae6dae\">10.3847/2041-8213/ae6dae</a>.","ama":"Chisholm J, Berg DA, Boylan-Kolchin M, et al. Little Red Dots as globular clusters in formation. <i>The Astrophysical Journal Letters</i>. 2026;1004(1). doi:<a href=\"https://doi.org/10.3847/2041-8213/ae6dae\">10.3847/2041-8213/ae6dae</a>","short":"J. Chisholm, D.A. Berg, M. Boylan-Kolchin, A. De Graaff, L.J. Furtak, V. Kokorev, J.J. Matthee, J.B. Muñoz, R.P. Naidu, A.A.C. Sander, The Astrophysical Journal Letters 1004 (2026).","apa":"Chisholm, J., Berg, D. A., Boylan-Kolchin, M., De Graaff, A., Furtak, L. J., Kokorev, V., … Sander, A. A. C. (2026). Little Red Dots as globular clusters in formation. <i>The Astrophysical Journal Letters</i>. IOP Publishing. <a href=\"https://doi.org/10.3847/2041-8213/ae6dae\">https://doi.org/10.3847/2041-8213/ae6dae</a>"},"date_created":"2026-06-14T22:01:42Z","month":"06","external_id":{"arxiv":["2602.15935"]},"author":[{"first_name":"John","last_name":"Chisholm","full_name":"Chisholm, John"},{"first_name":"Danielle A.","last_name":"Berg","full_name":"Berg, Danielle A."},{"first_name":"Michael","last_name":"Boylan-Kolchin","full_name":"Boylan-Kolchin, Michael"},{"first_name":"Anna","last_name":"De Graaff","full_name":"De Graaff, Anna"},{"last_name":"Furtak","first_name":"Lukas J.","full_name":"Furtak, Lukas J."},{"first_name":"Vasily","last_name":"Kokorev","full_name":"Kokorev, Vasily"},{"last_name":"Matthee","id":"7439a258-f3c0-11ec-9501-9df22fe06720","first_name":"Jorryt J","orcid":"0000-0003-2871-127X","full_name":"Matthee, Jorryt J"},{"last_name":"Muñoz","first_name":"Julian B.","full_name":"Muñoz, Julian B."},{"first_name":"Rohan P.","last_name":"Naidu","full_name":"Naidu, Rohan P."},{"full_name":"Sander, Andreas A.C.","first_name":"Andreas A.C.","last_name":"Sander"}],"has_accepted_license":"1","oa":1,"publication_identifier":{"issn":["2041-8205"],"eissn":["2041-8213"]},"intvolume":"      1004","file_date_updated":"2026-06-19T09:45:21Z","OA_place":"publisher","date_updated":"2026-06-19T09:50:33Z","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","ddc":["520"],"date_published":"2026-06-10T00:00:00Z","arxiv":1,"title":"Little Red Dots as globular clusters in formation","issue":"1","PlanS_conform":"1","day":"10","_id":"21998","language":[{"iso":"eng"}]},{"article_number":"244","volume":1003,"publication_status":"published","oa_version":"Published Version","tmp":{"name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","image":"/images/cc_by.png","short":"CC BY (4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode"},"publisher":"IOP Publishing","scopus_import":"1","dataavailabilitystatement":"10.17909/4byn-fe55 and 10.17909/v2y7-j922 used with Software: LMFIT (M. Newville et al. 2014) msafit (A. de Graaff et al. 2024). - Text extracted from Acknowledgements, no separate DAS","fulldoi":"https://doi.org/10.3847/1538-4357/ae6248","type":"journal_article","DOAJ_listed":"1","quality_controlled":"1","article_processing_charge":"Yes","publication":"The Astrophysical Journal","researchdata_availability":"yes","abstract":[{"lang":"eng","text":"JWST has revealed an abundance of supermassive black holes (BHs) in the early Universe, and yet the lowest mass seed BHs that gave rise to these populations remain elusive. Here, we present a systematic search for broad-line active galactic nuclei (AGNs) in some of the faintest high-z galaxies surveyed yet by combining ultra-deep JWST/NIRSpec G395M spectroscopy with the strong lensing aid in AS1063. By employing the profile of the [O iii]λ5007 emission lines as a template for narrow-line components and carefully cross-validating with mock observations, we identify a sample of 10 broad-line AGNs at 4.5 < z < 7.0 (eight secure, two tentative). The inferred BH masses from the broad Hα line explore the intermediate BH mass regime down to ∼105.5 M⊙. The stellar mass (M*) is estimated with a galaxy+AGN composite model, and we find the BH to stellar mass ratio spans down to MBH/M* ≲ 0.1%, unveiling populations on the empirical MBH–M* relation observed in the local Universe. We also derive the BH mass function and investigate its low-mass end at this epoch. While we confirm the agreement of our results with previous studies at MBH ≳ 106.5M⊙, we find the mass range of ∼105.5 M⊙ features an enhanced abundance with respect to the extrapolated best-fit Schechter function. Comparison with theoretical models suggests that a possible origin for this enhanced abundance is the direct-collapse BH formation, supporting the scenario that the direct collapse of massive gas clouds is a significant pathway for the earliest supermassive BHs."}],"article_type":"original","file":[{"creator":"dernst","checksum":"b04247996b8dcd0eb5387581706d1106","file_size":19681834,"file_name":"2026_AstrophysicalJour_Fei.pdf","success":1,"file_id":"22112","relation":"main_file","date_updated":"2026-06-22T08:03:55Z","date_created":"2026-06-22T08:03:55Z","content_type":"application/pdf","access_level":"open_access"}],"doi":"10.3847/1538-4357/ae6248","acknowledgement":"We thank the anonymous referee for insightful comments, which significantly improved the manuscript. We acknowledge Kohei Inayoshi for helpful discussions. This work is based on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. The specific observations analyzed can be accessed via DOI: 10.17909/4byn-fe55 and 10.17909/v2y7-j922. These observations are associated with programs #3293 and #9223. S.F. and Q.F. acknowledge support from the Dunlap Institute, which is funded through an endowment established by the David Dunlap family and the University of Toronto. A.S.L. acknowledges support from the Knut and Alice Wallenberg Foundation. A.Z. acknowledges support by grant No. 2020750 from the United States-Israel Binational Science Foundation (BSF) and grant No. 2109066 from the United States National Science Foundation (NSF); and by the Israel Science Foundation grant No. 864/23.","title":"A GLIMPSE of intermediate mass Black Holes in the epoch of reionization: Witnessing the descendants of direct collapse?","arxiv":1,"language":[{"iso":"eng"}],"_id":"21999","PlanS_conform":"1","day":"01","issue":"2","OA_place":"publisher","das_tickbox":"0","file_date_updated":"2026-06-22T08:03:55Z","intvolume":"      1003","publication_identifier":{"issn":["0004-637X"],"eissn":["1538-4357"]},"supplementarymaterial":"yes","ddc":["520"],"date_published":"2026-06-01T00:00:00Z","date_updated":"2026-06-22T11:34:52Z","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","external_id":{"arxiv":["2509.20452"]},"month":"06","has_accepted_license":"1","oa":1,"author":[{"first_name":"Qinyue","last_name":"Fei","full_name":"Fei, Qinyue"},{"first_name":"Seiji","last_name":"Fujimoto","full_name":"Fujimoto, Seiji"},{"full_name":"Naidu, Rohan P.","first_name":"Rohan P.","last_name":"Naidu"},{"last_name":"Chisholm","first_name":"John","full_name":"Chisholm, John"},{"full_name":"Atek, Hakim","first_name":"Hakim","last_name":"Atek"},{"full_name":"Brammer, Gabriel","last_name":"Brammer","first_name":"Gabriel"},{"full_name":"Asada, Yoshihisa","last_name":"Asada","first_name":"Yoshihisa"},{"last_name":"Berg","first_name":"Danielle A.","full_name":"Berg, Danielle A."},{"first_name":"Volker","last_name":"Bromm","full_name":"Bromm, Volker"},{"full_name":"Furtak, Lukas J.","last_name":"Furtak","first_name":"Lukas J."},{"full_name":"Greene, Jenny E.","last_name":"Greene","first_name":"Jenny E."},{"full_name":"Hsiao, Tiger Yu Yang","first_name":"Tiger Yu Yang","last_name":"Hsiao"},{"first_name":"Junehyoung","last_name":"Jeon","full_name":"Jeon, Junehyoung"},{"full_name":"Kokorev, Vasily","last_name":"Kokorev","first_name":"Vasily"},{"orcid":"0000-0003-2871-127X","full_name":"Matthee, Jorryt J","last_name":"Matthee","id":"7439a258-f3c0-11ec-9501-9df22fe06720","first_name":"Jorryt J"},{"full_name":"Natarajan, Priyamvada","last_name":"Natarajan","first_name":"Priyamvada"},{"full_name":"Pan, Richard","first_name":"Richard","last_name":"Pan"},{"full_name":"Richard, Johan","last_name":"Richard","first_name":"Johan"},{"last_name":"Saldana-Lopez","first_name":"Alberto","full_name":"Saldana-Lopez, Alberto"},{"last_name":"Schaerer","first_name":"Daniel","full_name":"Schaerer, Daniel"},{"full_name":"Volonteri, Marta","last_name":"Volonteri","first_name":"Marta"},{"full_name":"Zitrin, Adi","last_name":"Zitrin","first_name":"Adi"}],"status":"public","date_created":"2026-06-14T22:01:43Z","citation":{"ama":"Fei Q, Fujimoto S, Naidu RP, et al. A GLIMPSE of intermediate mass Black Holes in the epoch of reionization: Witnessing the descendants of direct collapse? <i>The Astrophysical Journal</i>. 2026;1003(2). doi:<a href=\"https://doi.org/10.3847/1538-4357/ae6248\">10.3847/1538-4357/ae6248</a>","short":"Q. Fei, S. Fujimoto, R.P. Naidu, J. Chisholm, H. Atek, G. Brammer, Y. Asada, D.A. Berg, V. Bromm, L.J. Furtak, J.E. Greene, T.Y.Y. Hsiao, J. Jeon, V. Kokorev, J.J. Matthee, P. Natarajan, R. Pan, J. Richard, A. Saldana-Lopez, D. Schaerer, M. Volonteri, A. Zitrin, The Astrophysical Journal 1003 (2026).","apa":"Fei, Q., Fujimoto, S., Naidu, R. P., Chisholm, J., Atek, H., Brammer, G., … Zitrin, A. (2026). A GLIMPSE of intermediate mass Black Holes in the epoch of reionization: Witnessing the descendants of direct collapse? <i>The Astrophysical Journal</i>. IOP Publishing. <a href=\"https://doi.org/10.3847/1538-4357/ae6248\">https://doi.org/10.3847/1538-4357/ae6248</a>","mla":"Fei, Qinyue, et al. “A GLIMPSE of Intermediate Mass Black Holes in the Epoch of Reionization: Witnessing the Descendants of Direct Collapse?” <i>The Astrophysical Journal</i>, vol. 1003, no. 2, 244, IOP Publishing, 2026, doi:<a href=\"https://doi.org/10.3847/1538-4357/ae6248\">10.3847/1538-4357/ae6248</a>.","chicago":"Fei, Qinyue, Seiji Fujimoto, Rohan P. Naidu, John Chisholm, Hakim Atek, Gabriel Brammer, Yoshihisa Asada, et al. “A GLIMPSE of Intermediate Mass Black Holes in the Epoch of Reionization: Witnessing the Descendants of Direct Collapse?” <i>The Astrophysical Journal</i>. IOP Publishing, 2026. <a href=\"https://doi.org/10.3847/1538-4357/ae6248\">https://doi.org/10.3847/1538-4357/ae6248</a>.","ista":"Fei Q, Fujimoto S, Naidu RP, Chisholm J, Atek H, Brammer G, Asada Y, Berg DA, Bromm V, Furtak LJ, Greene JE, Hsiao TYY, Jeon J, Kokorev V, Matthee JJ, Natarajan P, Pan R, Richard J, Saldana-Lopez A, Schaerer D, Volonteri M, Zitrin A. 2026. A GLIMPSE of intermediate mass Black Holes in the epoch of reionization: Witnessing the descendants of direct collapse? The Astrophysical Journal. 1003(2), 244.","ieee":"Q. Fei <i>et al.</i>, “A GLIMPSE of intermediate mass Black Holes in the epoch of reionization: Witnessing the descendants of direct collapse?,” <i>The Astrophysical Journal</i>, vol. 1003, no. 2. IOP Publishing, 2026."},"year":"2026","OA_type":"gold","department":[{"_id":"JoMa"}]},{"project":[{"grant_number":"101076224","name":"Young galaxies as tracers and agents of cosmic reionization","_id":"bd9b2118-d553-11ed-ba76-db24564edfea"}],"publication":"Monthly Notices of the Royal Astronomical Society","abstract":[{"text":"Little Red Dots (LRDs) are compact sources at z > 5 discovered through James Webb Space Telescope spectroscopy. Their spectra exhibit broad Balmer emission lines (>~1000 km s^−1), alongside absorption features and a pronounced Balmer break – evidence for a dense, neutral hydrogen medium, in which the n = 2 state is significantly populated. When interpreted as arising\r\nfrom active galactic nucleus broad-line regions, inferred black hole masses from local scaling relations exceed expectations given their stellar masses, challenging models of early black hole–galaxy co-evolution. However, radiative transfer effects in dense media may also impact the formation of hydrogen emission lines. We model three scattering processes shaping hydrogen\r\nline profiles: resonance scattering by hydrogen in the n = 2 state, Raman scattering of ultraviolet (UV) radiation by ground-state hydrogen, and Thomson scattering by free electrons. Using 3D Monte Carlo radiative transfer simulations, we examine their imprint on line shapes and ratios. Resonance scattering produces strong deviations from Case B flux ratios, clear differences\r\nbetween Hα and Hβ, and encodes gas kinematics in line profiles but cannot broaden Hβ due to conversion to Paα. While Raman scattering can yield broad wings, scattering of the UV continuum is disfavoured given the absence of strong full width at half-maximum variations across transitions. Raman scattering of higher Lyman-series emission can produce Hα/Hβ wing\r\nwidth ratios of  >~1.28, agreeing with observations. Thomson scattering can reproduce the observed >~ 1000 km s^−1 wings under plausible conditions – e.g. Te ∼ 10^4 K and Ne ∼ 10^24 cm^−2 – and lead to black hole mass overestimates by factors  10. Our results provide a framework for interpreting hydrogen lines in LRDs and similar systems.","lang":"eng"}],"article_type":"original","quality_controlled":"1","article_processing_charge":"Yes","doi":"10.1093/mnras/staf2131","acknowledgement":"The authorsthank the anonymousreferee for constructive comments, which improved the clarity of this paper. SJC acknowledges support from the ERC synergy grant 101166930 – RECAP. MG thanks the Max Planck Society for support through the Max Planck Research Group, and the European Union forsupport through ERC-2024-STG 101165038 (ReMMU). JM acknowledges funding by the European Union (ERC, AGENTS, 101076224). CAM acknowledges support\r\nby the European Union ERC grant RISES (101163035), Carlsberg Foundation (CF22-1322), and VILLUM FONDEN (37459). Computations were performed on HPC systems Freya and Orion at the Max Planck Computing and Data Facility.","file":[{"date_updated":"2026-02-12T12:44:33Z","date_created":"2026-02-12T12:44:33Z","content_type":"application/pdf","access_level":"open_access","file_name":"2026_MonthNoticesRAS_Chang.pdf","file_size":5600366,"creator":"dernst","checksum":"52ba7d7b5b80af0c50f57e4c2acc3930","file_id":"21220","success":1,"relation":"main_file"}],"publication_status":"published","oa_version":"Published Version","article_number":"staf2131","volume":545,"fulldoi":"https://doi.org/10.1093/mnras/staf2131","DOAJ_listed":"1","type":"journal_article","tmp":{"name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","image":"/images/cc_by.png","short":"CC BY (4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode"},"publisher":"Oxford University Press","scopus_import":"1","oa":1,"has_accepted_license":"1","author":[{"last_name":"Chang","first_name":"Seok Jun","full_name":"Chang, Seok Jun"},{"last_name":"Gronke","first_name":"Max","full_name":"Gronke, Max"},{"last_name":"Matthee","id":"7439a258-f3c0-11ec-9501-9df22fe06720","first_name":"Jorryt J","orcid":"0000-0003-2871-127X","full_name":"Matthee, Jorryt J"},{"full_name":"Mason, Charlotte","last_name":"Mason","first_name":"Charlotte"}],"external_id":{"arxiv":["2508.08768"]},"month":"02","date_created":"2026-01-25T23:01:39Z","citation":{"mla":"Chang, Seok Jun, et al. “Impact of Resonance, Raman, and Thomson Scattering on Hydrogen Line Formation in Little Red Dots.” <i>Monthly Notices of the Royal Astronomical Society</i>, vol. 545, no. 4, staf2131, Oxford University Press, 2026, doi:<a href=\"https://doi.org/10.1093/mnras/staf2131\">10.1093/mnras/staf2131</a>.","apa":"Chang, S. J., Gronke, M., Matthee, J. J., &#38; Mason, C. (2026). Impact of resonance, Raman, and Thomson scattering on hydrogen line formation in Little Red Dots. <i>Monthly Notices of the Royal Astronomical Society</i>. Oxford University Press. <a href=\"https://doi.org/10.1093/mnras/staf2131\">https://doi.org/10.1093/mnras/staf2131</a>","short":"S.J. Chang, M. Gronke, J.J. Matthee, C. Mason, Monthly Notices of the Royal Astronomical Society 545 (2026).","ama":"Chang SJ, Gronke M, Matthee JJ, Mason C. Impact of resonance, Raman, and Thomson scattering on hydrogen line formation in Little Red Dots. <i>Monthly Notices of the Royal Astronomical Society</i>. 2026;545(4). doi:<a href=\"https://doi.org/10.1093/mnras/staf2131\">10.1093/mnras/staf2131</a>","ieee":"S. J. Chang, M. Gronke, J. J. Matthee, and C. Mason, “Impact of resonance, Raman, and Thomson scattering on hydrogen line formation in Little Red Dots,” <i>Monthly Notices of the Royal Astronomical Society</i>, vol. 545, no. 4. Oxford University Press, 2026.","chicago":"Chang, Seok Jun, Max Gronke, Jorryt J Matthee, and Charlotte Mason. “Impact of Resonance, Raman, and Thomson Scattering on Hydrogen Line Formation in Little Red Dots.” <i>Monthly Notices of the Royal Astronomical Society</i>. Oxford University Press, 2026. <a href=\"https://doi.org/10.1093/mnras/staf2131\">https://doi.org/10.1093/mnras/staf2131</a>.","ista":"Chang SJ, Gronke M, Matthee JJ, Mason C. 2026. Impact of resonance, Raman, and Thomson scattering on hydrogen line formation in Little Red Dots. Monthly Notices of the Royal Astronomical Society. 545(4), staf2131."},"OA_type":"gold","year":"2026","department":[{"_id":"JoMa"}],"status":"public","_id":"21038","language":[{"iso":"eng"}],"day":"01","PlanS_conform":"1","issue":"4","title":"Impact of resonance, Raman, and Thomson scattering on hydrogen line formation in Little Red Dots","arxiv":1,"date_updated":"2026-02-12T12:56:33Z","ddc":["520"],"date_published":"2026-02-01T00:00:00Z","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","OA_place":"publisher","file_date_updated":"2026-02-12T12:44:33Z","intvolume":"       545","publication_identifier":{"issn":["0035-8711"],"eissn":["1365-2966"]}},{"status":"public","department":[{"_id":"JoMa"},{"_id":"GradSch"}],"citation":{"ama":"Kotiwale G, Matthee JJ, Kashino D, et al. Rapid, out-of-equilibrium metal enrichment indicated by a flat mass-metallicity relation at z ∼ 6 from NIRCam grism spectroscopy. <i>Astronomy &#38; Astrophysics</i>. 2026;706. doi:<a href=\"https://doi.org/10.1051/0004-6361/202556597\">10.1051/0004-6361/202556597</a>","short":"G. Kotiwale, J.J. Matthee, D. Kashino, A.P. Vijayan, A. Torralba Torregrosa, C. Di Cesare, E. Iani, R. Bordoloi, J. Leja, M.V. Maseda, S. Tacchella, I. Shivaei, K.E. Heintz, A.L. Danhaive, S. Mascia, I. Kramarenko, B. Navarrete, R. Mackenzie, R.P. Naidu, D. Sobral, Astronomy &#38; Astrophysics 706 (2026).","apa":"Kotiwale, G., Matthee, J. J., Kashino, D., Vijayan, A. P., Torralba Torregrosa, A., Di Cesare, C., … Sobral, D. (2026). Rapid, out-of-equilibrium metal enrichment indicated by a flat mass-metallicity relation at z ∼ 6 from NIRCam grism spectroscopy. <i>Astronomy &#38; Astrophysics</i>. EDP Sciences. <a href=\"https://doi.org/10.1051/0004-6361/202556597\">https://doi.org/10.1051/0004-6361/202556597</a>","mla":"Kotiwale, Gauri, et al. “Rapid, out-of-Equilibrium Metal Enrichment Indicated by a Flat Mass-Metallicity Relation at z ∼ 6 from NIRCam Grism Spectroscopy.” <i>Astronomy &#38; Astrophysics</i>, vol. 706, A165, EDP Sciences, 2026, doi:<a href=\"https://doi.org/10.1051/0004-6361/202556597\">10.1051/0004-6361/202556597</a>.","ista":"Kotiwale G, Matthee JJ, Kashino D, Vijayan AP, Torralba Torregrosa A, Di Cesare C, Iani E, Bordoloi R, Leja J, Maseda MV, Tacchella S, Shivaei I, Heintz KE, Danhaive AL, Mascia S, Kramarenko I, Navarrete B, Mackenzie R, Naidu RP, Sobral D. 2026. Rapid, out-of-equilibrium metal enrichment indicated by a flat mass-metallicity relation at z ∼ 6 from NIRCam grism spectroscopy. Astronomy &#38; Astrophysics. 706, A165.","chicago":"Kotiwale, Gauri, Jorryt J Matthee, Daichi Kashino, Aswin P. Vijayan, Alberto Torralba Torregrosa, Claudia Di Cesare, Edoardo Iani, et al. “Rapid, out-of-Equilibrium Metal Enrichment Indicated by a Flat Mass-Metallicity Relation at z ∼ 6 from NIRCam Grism Spectroscopy.” <i>Astronomy &#38; Astrophysics</i>. EDP Sciences, 2026. <a href=\"https://doi.org/10.1051/0004-6361/202556597\">https://doi.org/10.1051/0004-6361/202556597</a>.","ieee":"G. Kotiwale <i>et al.</i>, “Rapid, out-of-equilibrium metal enrichment indicated by a flat mass-metallicity relation at z ∼ 6 from NIRCam grism spectroscopy,” <i>Astronomy &#38; Astrophysics</i>, vol. 706. EDP Sciences, 2026."},"date_created":"2026-02-22T23:01:35Z","OA_type":"diamond","year":"2026","month":"02","external_id":{"arxiv":["2510.19959"]},"author":[{"full_name":"Kotiwale, Gauri","first_name":"Gauri","id":"1438afc8-1ff6-11ee-9fa6-cd4a75d66875","last_name":"Kotiwale"},{"first_name":"Jorryt J","id":"7439a258-f3c0-11ec-9501-9df22fe06720","last_name":"Matthee","orcid":"0000-0003-2871-127X","full_name":"Matthee, Jorryt J"},{"first_name":"Daichi","last_name":"Kashino","full_name":"Kashino, Daichi"},{"full_name":"Vijayan, Aswin P.","last_name":"Vijayan","first_name":"Aswin P."},{"full_name":"Torralba Torregrosa, Alberto","orcid":"0000-0001-5586-6950","first_name":"Alberto","last_name":"Torralba Torregrosa","id":"018f0249-0e87-11f0-b167-cbce08fbd541"},{"full_name":"Di Cesare, Claudia","last_name":"Di Cesare","id":"2d002343-372f-11ef-98ec-a164d20427cb","first_name":"Claudia"},{"orcid":"0000-0001-8386-3546","full_name":"Iani, Edoardo","first_name":"Edoardo","id":"4053390a-6b68-11ef-9828-a3b8adef8d0a","last_name":"Iani"},{"full_name":"Bordoloi, Rongmon","last_name":"Bordoloi","first_name":"Rongmon"},{"full_name":"Leja, Joel","last_name":"Leja","first_name":"Joel"},{"last_name":"Maseda","first_name":"Michael V.","full_name":"Maseda, Michael V."},{"last_name":"Tacchella","first_name":"Sandro","full_name":"Tacchella, Sandro"},{"full_name":"Shivaei, Irene","first_name":"Irene","last_name":"Shivaei"},{"full_name":"Heintz, Kasper E.","first_name":"Kasper E.","last_name":"Heintz"},{"first_name":"A. Lola","last_name":"Danhaive","full_name":"Danhaive, A. Lola"},{"first_name":"Sara","last_name":"Mascia","id":"edaf889c-c7cd-11ef-ab1b-bb28c431bd29","full_name":"Mascia, Sara"},{"first_name":"Ivan","last_name":"Kramarenko","id":"9a9394cb-3200-11ee-973b-f5ba2a8b16e4","orcid":"0000-0001-5346-6048","full_name":"Kramarenko, Ivan"},{"full_name":"Navarrete, Benjamín","first_name":"Benjamín","last_name":"Navarrete","id":"aa14a535-50c9-11ef-b52e-e0c373d10148"},{"last_name":"Mackenzie","first_name":"Ruari","full_name":"Mackenzie, Ruari"},{"full_name":"Naidu, Rohan P.","last_name":"Naidu","first_name":"Rohan P."},{"full_name":"Sobral, David","first_name":"David","last_name":"Sobral"}],"oa":1,"has_accepted_license":"1","file_date_updated":"2026-02-24T07:46:47Z","publication_identifier":{"issn":["0004-6361"],"eissn":["1432-0746"]},"intvolume":"       706","OA_place":"publisher","date_published":"2026-02-01T00:00:00Z","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","ddc":["520"],"date_updated":"2026-02-24T07:49:42Z","arxiv":1,"title":"Rapid, out-of-equilibrium metal enrichment indicated by a flat mass-metallicity relation at z ∼ 6 from NIRCam grism spectroscopy","PlanS_conform":"1","day":"01","language":[{"iso":"eng"}],"_id":"21341","file":[{"relation":"main_file","file_id":"21355","success":1,"file_size":6531719,"file_name":"2026_AstronomyAstrophysics_Kotiwale.pdf","creator":"dernst","checksum":"6f5849d29ad43bee32f90152f6fc0294","access_level":"open_access","content_type":"application/pdf","date_created":"2026-02-24T07:46:47Z","date_updated":"2026-02-24T07:46:47Z"}],"acknowledgement":"We thank the anonymous referee for the insightful comments that helped improving this paper. This work is based on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Associations of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These observations were taken under programmes # 1243, # 1933 and # 3516. Funded by the European Union (ERC, AGENTS, 101076224). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them. GK acknowledges support from the Foundation MERAC. APV acknowledge support from the Sussex Astronomy Centre STFC Consolidated Grant (ST/X001040/1).","doi":"10.1051/0004-6361/202556597","article_processing_charge":"No","quality_controlled":"1","article_type":"original","abstract":[{"text":"We aim to characterise the mass-metallicity relation (MZR) and the 3D correlation between the stellar mass, metallicity, and star formation rate (SFR) known as the fundamental metallicity relation (FMR) for galaxies at 5 < z < 7. Using ∼800 [O III] selected galaxies from deep NIRCam grism surveys, we present our stacked measurements of direct-Te metallicities, which we used to test recent strong-line metallicity calibrations. Our measured direct-Te metallicities (0.1–0.2 Z⊙ for M★ ≈ 5 × 107 − 9 M⊙, respectively) match recent JWST/NIRSpec-based results. However, there are significant inconsistencies between observations and hydrodynamical simulations. We observe a flatter MZR slope than the SPHINX20 and FLARES simulations, which cannot be attributed to selection effects. With simple models, we show that the effect of an [O III] flux-limited sample on the observed shape of the MZR is strongly dependent on the FMR. If the FMR is similar to the one in the local Universe, the intrinsic high-redshift MZR should be even flatter than is observed. In turn, a 3D relation where SFR correlates positively with metallicity at fixed mass would imply an intrinsically steeper MZR. Our measurements indicate that metallicity variations at fixed mass show little dependence on the SFR, suggesting a flat intrinsic MZR. This could indicate that the low-mass galaxies at these redshifts are out of equilibrium and that metal enrichment occurs rapidly in low-mass galaxies. However, being limited by our stacking analysis, we are yet to probe the scatter in the MZR and its dependence on SFR. Large carefully selected samples of galaxies with robust metallicity measurements can put tight constraints on the high-redshift FMR and help us to understand the interplay between gas flows, star formation, and feedback in early galaxies.","lang":"eng"}],"project":[{"_id":"bd9b2118-d553-11ed-ba76-db24564edfea","name":"Young galaxies as tracers and agents of cosmic reionization","grant_number":"101076224"}],"publication":"Astronomy & Astrophysics","scopus_import":"1","tmp":{"name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","image":"/images/cc_by.png","short":"CC BY (4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode"},"publisher":"EDP Sciences","fulldoi":"https://doi.org/10.1051/0004-6361/202556597","type":"journal_article","DOAJ_listed":"1","article_number":"A165","volume":706,"publication_status":"published","oa_version":"Published Version","corr_author":"1"},{"intvolume":"         9","publication_identifier":{"eissn":["2565-6120"]},"OA_place":"publisher","ddc":["520"],"date_updated":"2026-06-16T10:47:41Z","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","date_published":"2026-01-30T00:00:00Z","arxiv":1,"title":"A cosmic miracle: A remarkably luminous galaxy at zspec = 14.44 confirmed with JWST","PlanS_conform":"1","day":"30","language":[{"iso":"eng"}],"_id":"21342","status":"public","department":[{"_id":"JoMa"}],"year":"2026","OA_type":"diamond","citation":{"ieee":"R. P. Naidu <i>et al.</i>, “A cosmic miracle: A remarkably luminous galaxy at zspec = 14.44 confirmed with JWST,” <i>The Open Journal of Astrophysics</i>, vol. 9. Maynooth Academic Publishing, 2026.","chicago":"Naidu, Rohan P., Pascal A. Oesch, Gabriel Brammer, Andrea Weibel, Yijia Li, Jorryt J Matthee, John Chisholm, et al. “A Cosmic Miracle: A Remarkably Luminous Galaxy at Zspec = 14.44 Confirmed with JWST.” <i>The Open Journal of Astrophysics</i>. Maynooth Academic Publishing, 2026. <a href=\"https://doi.org/10.33232/001c.156033\">https://doi.org/10.33232/001c.156033</a>.","ista":"Naidu RP, Oesch PA, Brammer G, Weibel A, Li Y, Matthee JJ, Chisholm J, Pollock CL, Heintz KE, Johnson BD, Shen X, Hviding RE, Leja J, Tacchella S, Ganguly A, Witten C, Atek H, Belli S, Bose S, Bouwens R, Dayal P, Decarli R, De Graaff A, Fudamoto Y, Giovinazzo E, Greene JE, Illingworth G, Inoue AK, Kane SG, Labbe I, Leonova E, Marques-Chaves R, Meyer RA, Nelson EJ, Roberts-Borsani G, Schaerer D, Simcoe RA, Stefanon M, Sugahara Y, Toft S, Van Der Wel A, Van Dokkum P, Walter F, Watson D, Weaver JR, Whitaker KE. 2026. A cosmic miracle: A remarkably luminous galaxy at zspec = 14.44 confirmed with JWST. The Open Journal of Astrophysics. 9.","short":"R.P. Naidu, P.A. Oesch, G. Brammer, A. Weibel, Y. Li, J.J. Matthee, J. Chisholm, C.L. Pollock, K.E. Heintz, B.D. Johnson, X. Shen, R.E. Hviding, J. Leja, S. Tacchella, A. Ganguly, C. Witten, H. Atek, S. Belli, S. Bose, R. Bouwens, P. Dayal, R. Decarli, A. De Graaff, Y. Fudamoto, E. Giovinazzo, J.E. Greene, G. Illingworth, A.K. Inoue, S.G. Kane, I. Labbe, E. Leonova, R. Marques-Chaves, R.A. Meyer, E.J. Nelson, G. Roberts-Borsani, D. Schaerer, R.A. Simcoe, M. Stefanon, Y. Sugahara, S. Toft, A. Van Der Wel, P. Van Dokkum, F. Walter, D. Watson, J.R. Weaver, K.E. Whitaker, The Open Journal of Astrophysics 9 (2026).","apa":"Naidu, R. P., Oesch, P. A., Brammer, G., Weibel, A., Li, Y., Matthee, J. J., … Whitaker, K. E. (2026). A cosmic miracle: A remarkably luminous galaxy at zspec = 14.44 confirmed with JWST. <i>The Open Journal of Astrophysics</i>. Maynooth Academic Publishing. <a href=\"https://doi.org/10.33232/001c.156033\">https://doi.org/10.33232/001c.156033</a>","ama":"Naidu RP, Oesch PA, Brammer G, et al. A cosmic miracle: A remarkably luminous galaxy at zspec = 14.44 confirmed with JWST. <i>The Open Journal of Astrophysics</i>. 2026;9. doi:<a href=\"https://doi.org/10.33232/001c.156033\">10.33232/001c.156033</a>","mla":"Naidu, Rohan P., et al. “A Cosmic Miracle: A Remarkably Luminous Galaxy at Zspec = 14.44 Confirmed with JWST.” <i>The Open Journal of Astrophysics</i>, vol. 9, Maynooth Academic Publishing, 2026, doi:<a href=\"https://doi.org/10.33232/001c.156033\">10.33232/001c.156033</a>."},"date_created":"2026-02-22T23:01:35Z","month":"01","external_id":{"arxiv":["2505.11263"]},"author":[{"full_name":"Naidu, Rohan P.","first_name":"Rohan P.","last_name":"Naidu"},{"full_name":"Oesch, Pascal A.","first_name":"Pascal A.","last_name":"Oesch"},{"first_name":"Gabriel","last_name":"Brammer","full_name":"Brammer, Gabriel"},{"first_name":"Andrea","last_name":"Weibel","full_name":"Weibel, Andrea"},{"full_name":"Li, Yijia","last_name":"Li","first_name":"Yijia"},{"first_name":"Jorryt J","last_name":"Matthee","id":"7439a258-f3c0-11ec-9501-9df22fe06720","full_name":"Matthee, Jorryt J","orcid":"0000-0003-2871-127X"},{"first_name":"John","last_name":"Chisholm","full_name":"Chisholm, John"},{"full_name":"Pollock, Clara L.","first_name":"Clara L.","last_name":"Pollock"},{"full_name":"Heintz, Kasper E.","last_name":"Heintz","first_name":"Kasper E."},{"full_name":"Johnson, Benjamin D.","last_name":"Johnson","first_name":"Benjamin D."},{"full_name":"Shen, Xuejian","first_name":"Xuejian","last_name":"Shen"},{"last_name":"Hviding","first_name":"Raphael E.","full_name":"Hviding, Raphael E."},{"full_name":"Leja, Joel","last_name":"Leja","first_name":"Joel"},{"full_name":"Tacchella, Sandro","first_name":"Sandro","last_name":"Tacchella"},{"full_name":"Ganguly, Arpita","first_name":"Arpita","last_name":"Ganguly"},{"full_name":"Witten, Callum","last_name":"Witten","first_name":"Callum"},{"full_name":"Atek, Hakim","last_name":"Atek","first_name":"Hakim"},{"full_name":"Belli, Sirio","last_name":"Belli","first_name":"Sirio"},{"full_name":"Bose, Sownak","first_name":"Sownak","last_name":"Bose"},{"last_name":"Bouwens","first_name":"Rychard","full_name":"Bouwens, Rychard"},{"full_name":"Dayal, Pratika","first_name":"Pratika","last_name":"Dayal"},{"first_name":"Roberto","last_name":"Decarli","full_name":"Decarli, Roberto"},{"first_name":"Anna","last_name":"De Graaff","full_name":"De Graaff, Anna"},{"full_name":"Fudamoto, Yoshinobu","first_name":"Yoshinobu","last_name":"Fudamoto"},{"full_name":"Giovinazzo, Emma","last_name":"Giovinazzo","first_name":"Emma"},{"last_name":"Greene","first_name":"Jenny E.","full_name":"Greene, Jenny E."},{"full_name":"Illingworth, Garth","first_name":"Garth","last_name":"Illingworth"},{"full_name":"Inoue, Akio K.","first_name":"Akio K.","last_name":"Inoue"},{"full_name":"Kane, Sarah G.","last_name":"Kane","first_name":"Sarah G."},{"first_name":"Ivo","last_name":"Labbe","full_name":"Labbe, Ivo"},{"full_name":"Leonova, Ecaterina","last_name":"Leonova","first_name":"Ecaterina"},{"last_name":"Marques-Chaves","first_name":"Rui","full_name":"Marques-Chaves, Rui"},{"last_name":"Meyer","first_name":"Romain A.","full_name":"Meyer, Romain A."},{"first_name":"Erica J.","last_name":"Nelson","full_name":"Nelson, Erica J."},{"last_name":"Roberts-Borsani","first_name":"Guido","full_name":"Roberts-Borsani, Guido"},{"full_name":"Schaerer, Daniel","first_name":"Daniel","last_name":"Schaerer"},{"full_name":"Simcoe, Robert A.","last_name":"Simcoe","first_name":"Robert A."},{"full_name":"Stefanon, Mauro","first_name":"Mauro","last_name":"Stefanon"},{"last_name":"Sugahara","first_name":"Yuma","full_name":"Sugahara, Yuma"},{"full_name":"Toft, Sune","last_name":"Toft","first_name":"Sune"},{"last_name":"Van Der Wel","first_name":"Arjen","full_name":"Van Der Wel, Arjen"},{"last_name":"Van Dokkum","first_name":"Pieter","full_name":"Van Dokkum, Pieter"},{"full_name":"Walter, Fabian","last_name":"Walter","first_name":"Fabian"},{"first_name":"Darach","last_name":"Watson","full_name":"Watson, Darach"},{"first_name":"John R.","last_name":"Weaver","full_name":"Weaver, John R."},{"first_name":"Katherine E.","last_name":"Whitaker","full_name":"Whitaker, Katherine E."}],"has_accepted_license":"1","oa":1,"main_file_link":[{"open_access":"1","url":"https://doi.org/10.33232/001c.156033"}],"scopus_import":"1","publisher":"Maynooth Academic Publishing","tmp":{"name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","image":"/images/cc_by.png","short":"CC BY (4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode"},"type":"journal_article","fulldoi":"https://doi.org/10.33232/001c.156033","volume":9,"oa_version":"Published Version","publication_status":"published","acknowledgement":"We thank the two anonymous referees for their insightful comments that have strengthened this work. “Mirage or Miracle” is but the latest link in a long chain of surveys that have built COSMOS into a premier extragalactic legacy field. We are thankful to all the teams who have contributed to this legacy, particularly those mentioned in §3 for leading recent JWST programs whose imaging\r\nwe have incorporated in our analysis. We are grateful to Vasily Belokurov for help in compiling the Milky Way reference sample featured in Fig 8. We thank Danielle Berg for sharing a highly complete, highly decimalized NUV vacuum line list. We are grateful to our program’s NIRSpec reviewer, Dan Coe, and program coordinator, Allison Vick, for valuable input on our MSA design. We acknowledge illuminating conversations with Risa Wechsler and Chao-Lin Kuo about early reionization. RPN thanks Neil Pappalardo and Jane Pappalardo for their generous support of the MIT Pappalardo Fellowships in Physics, and for their enthusiasm and encouragement for seeking galaxies at the highest redshifts. RPN acknowledges funding from JWST program GO5224. Support for this work was provided by NASA through the NASA Hubble Fellowship grant HST-HF2-51515.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. This work has received funding from the Swiss State Secretariat for Education, Research and Innovation (SERI) under contract number MB22.00072, as well as from the Swiss National Science Foundation (SNSF) through project grant 200020 207349. Funded by the European Union (ERC, AGENTS, 101076224 and HEAVYMETAL, 101071865). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of\r\nthe European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them. The Cosmic Dawn Center (DAWN) is funded by the Danish National Research Foundation under grant DNRF140. This work has also been supported by JSPS KAKENHI Grant Number 23H00131. HA acknowledges support from CNES, focused on the JWST mission, and the Programme National Cosmology and Galaxies (PNCG)\r\nof CNRS/INSU with INP and IN2P3, co-funded by CEA and CNES. HA is supported by the French National Research Agency (ANR) under the project FIRSTGAL, grant number ANR-24-CE31-0838. SB is supported by the UK Research and Innovation (UKRI) Future Leaders Fellowship [grant number MR/V023381/1]. R.D. acknowledges support from the INAF GO 2022\r\ngrant “The birth of the giants: JWST sheds light on the build-up of quasars at cosmic dawn” and by the PRIN MUR “2022935STW”, RFF M4.C2.1.1, CUP J53D23001570006 and C53D23000950006. Computations supporting this paper were run on MIT’s Engaging cluster. This publication made use of the NASA Astrophysical Data System for bibliographic information. Some of the data products presented herein were retrieved from the Dawn JWST Archive (DJA). DJA is an initiative of the Cosmic Dawn Center (DAWN), which is funded by the Danish National Research Foundation under grant DNRF140. Software used in developing this work includes: matplotlib (Hunter 2007), jupyter (Kluyver et al. 2016), IPython (P´erez & Granger 2007), numpy (Oliphant 2015), scipy (Virtanen et al. 2020), TOPCAT (Taylor 2005), and Astropy (Astropy Collaboration et al. 2013).This work is based on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space\r\nTelescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These observations are associated with program # 5224.","doi":"10.33232/001c.156033","article_processing_charge":"No","quality_controlled":"1","article_type":"original","abstract":[{"text":"JWST has revealed a stunning population of bright galaxies at surprisingly early epochs, z > 10,\r\nwhere few such sources were expected. Here we present the most distant example of this class yet – MoM-z14, a luminous (MUV = −20.2) source in the COSMOS legacy field at zspec = 14.44+0.02−0.02 that expands the observational frontier to a mere 280 million years after the Big Bang. The redshift is confirmed with NIRSpec/prism spectroscopy through a sharp Lyman-α break and ≈ 3σ detections of five rest-UV emission lines. The number density of bright zspec ≈ 14 − 15 sources implied by our “Mirage or Miracle” survey spanning ≈ 350 arcmin2 is > 100× larger (182+329 −105×) than pre-JWST consensus models. The high EWs of UV lines (≈15−35˚A) signal a rising star-formation history, with a ≈10× increase in the last 5 Myr (SFR5Myr/SFR50Myr = 9.9 +3.0 −5.8). The source is extremely compact (circularized re = 74+15\r\n−12 pc), and yet elongated (b/a = 0.25+0.11−0.06), suggesting an AGN is not the dominant source of UV light. The steep UV slope (β = −2.5 +0.2 −0.2) implies negligible dust attenuation\r\nand a young stellar population. The absence of a strong damping wing provides tentative evidence that the immediate surroundings of MoM-z14 may be partially ionized at a redshift where virtually every reionization model predicts a ≈ 100% neutral fraction. The nitrogen emission and highly supersolar [N/C]> 1 hint at an abundance pattern similar to local globular clusters that may have once hosted luminous supermassive stars. Since this abundance pattern is also common among the most ancient stars born in the Milky Way, we may be directly witnessing the formation of such stars in dense clusters, connecting galaxy evolution across the entire sweep of cosmic time. ","lang":"eng"}],"publication":"The Open Journal of Astrophysics","project":[{"_id":"bd9b2118-d553-11ed-ba76-db24564edfea","name":"Young galaxies as tracers and agents of cosmic reionization","grant_number":"101076224"}]},{"external_id":{"pmid":["41712710"]},"month":"02","author":[{"orcid":"0000-0003-2871-127X","full_name":"Matthee, Jorryt J","first_name":"Jorryt J","last_name":"Matthee","id":"7439a258-f3c0-11ec-9501-9df22fe06720"}],"status":"public","year":"2026","OA_type":"closed access","date_created":"2026-03-01T23:01:39Z","citation":{"ista":"Matthee JJ. 2026. Black holes disguised as little red dots. Science. 391(6787), 767–768.","chicago":"Matthee, Jorryt J. “Black Holes Disguised as Little Red Dots.” <i>Science</i>. AAAS, 2026. <a href=\"https://doi.org/10.1126/science.adz8603\">https://doi.org/10.1126/science.adz8603</a>.","ieee":"J. J. Matthee, “Black holes disguised as little red dots,” <i>Science</i>, vol. 391, no. 6787. AAAS, pp. 767–768, 2026.","mla":"Matthee, Jorryt J. “Black Holes Disguised as Little Red Dots.” <i>Science</i>, vol. 391, no. 6787, AAAS, 2026, pp. 767–68, doi:<a href=\"https://doi.org/10.1126/science.adz8603\">10.1126/science.adz8603</a>.","ama":"Matthee JJ. Black holes disguised as little red dots. <i>Science</i>. 2026;391(6787):767-768. doi:<a href=\"https://doi.org/10.1126/science.adz8603\">10.1126/science.adz8603</a>","apa":"Matthee, J. J. (2026). Black holes disguised as little red dots. <i>Science</i>. AAAS. <a href=\"https://doi.org/10.1126/science.adz8603\">https://doi.org/10.1126/science.adz8603</a>","short":"J.J. Matthee, Science 391 (2026) 767–768."},"department":[{"_id":"JoMa"}],"title":"Black holes disguised as little red dots","language":[{"iso":"eng"}],"_id":"21371","issue":"6787","pmid":1,"day":"19","publication_identifier":{"eissn":["1095-9203"]},"intvolume":"       391","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","date_published":"2026-02-19T00:00:00Z","date_updated":"2026-03-02T09:15:45Z","quality_controlled":"1","article_processing_charge":"No","publication":"Science","project":[{"name":"Young galaxies as tracers and agents of cosmic reionization","grant_number":"101076224","_id":"bd9b2118-d553-11ed-ba76-db24564edfea"}],"article_type":"comment","abstract":[{"text":"There may be a newly identified early phase of supermassive black hole growth","lang":"eng"}],"doi":"10.1126/science.adz8603","acknowledgement":"The author acknowledges the support from the European Union (European Research Council, AGENTS, 101076224).","volume":391,"page":"767-768","corr_author":"1","oa_version":"None","publication_status":"published","publisher":"AAAS","scopus_import":"1","type":"journal_article","fulldoi":"https://doi.org/10.1126/science.adz8603"},{"corr_author":"1","publication_status":"published","oa_version":"Published Version","article_number":"A75","volume":707,"fulldoi":"https://doi.org/10.1051/0004-6361/202557537","type":"journal_article","DOAJ_listed":"1","tmp":{"name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","image":"/images/cc_by.png","short":"CC BY (4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode"},"publisher":"EDP Sciences","scopus_import":"1","project":[{"_id":"bd9b2118-d553-11ed-ba76-db24564edfea","name":"Young galaxies as tracers and agents of cosmic reionization","grant_number":"101076224"}],"publication":"Astronomy & Astrophysics","article_type":"original","abstract":[{"lang":"eng","text":"The population of the little red dots (LRDs) may represent a key phase of supermassive black hole (SMBH) growth. A cocoon of dense excited gas is emerging as a key component to explain the most striking properties of LRDs, such as strong Balmer breaks and Balmer absorption, as well as the weak IR emission. To dissect the structure of LRDs, we analyzed new deep JWST/NIRSpec PRISM and G395H spectra of FRESCO-GN-9771, one of the most luminous known LRDs at z = 5.5. These spectra reveal a strong Balmer break, broad Balmer lines, and very narrow [O III] emission. We revealed a forest of optical [Fe II] lines, which we argue are emerging from a dense (nH = 109 − 10 cm−3) warm layer with electron temperature Te ≈ 7000 K. The broad wings of Hα and Hβ have an exponential profile due to electron scattering in this same layer. The high Hα : Hβ : Hγ flux ratio of ≈10.4 : 1 : 0.14 is an indicator of collisional excitation and resonant scattering dominating the Balmer line emission. A narrow Hγ component, unseen in the other two Balmer lines due to outshining by the broad components, could trace the ISM of a normal host galaxy with a star formation rate of ∼5 M⊙ yr−1. The warm layer is mostly opaque to Balmer transitions, producing a characteristic P Cygni profile in the line centers suggesting outflowing motions. This same layer is responsible for shaping the Balmer break. The broadband spectrum can be reasonably matched by a simple photoionized slab model that dominates the λ > 1500 Å continuum and a low-mass (∼108 M⊙) galaxy that could explain the narrow [O III], with only a subdominant contribution to the UV continuum. Our findings indicate that Balmer lines are not directly tracing the gas kinematics near the SMBH and that the BH mass scale is likely much lower than virial indicators suggest."}],"quality_controlled":"1","article_processing_charge":"No","doi":"10.1051/0004-6361/202557537","acknowledgement":"We thank the scientific referee for useful and constructive comments. We thank Ylva Götberg and Zoltan Haiman for insightful discussions about the physics of gaseous envelopes and accretion into black holes. Funded by the European Union (ERC, AGENTS, 101076224). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them. This work is based in part on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These observations are associated with program #5664. This work has received funding from the Swiss State Secretariat for Education, Research and Innovation (SERI) under contract number MB22.00072, as well as from the Swiss National Science Foundation (SNSF) through project grant 200020_207349.","file":[{"file_id":"21460","success":1,"file_name":"2026_AstronomyAstrophysics_Torralba2.pdf","creator":"dernst","checksum":"fcab9cb3dcf1d68612e1fdc8191643c1","file_size":2510157,"relation":"main_file","date_updated":"2026-03-16T10:57:49Z","date_created":"2026-03-16T10:57:49Z","access_level":"open_access","content_type":"application/pdf"}],"_id":"21451","language":[{"iso":"eng"}],"day":"01","PlanS_conform":"1","title":"The warm outer layer of a little red dot as the source of [Fe ii] and collisional Balmer lines with scattering wings","arxiv":1,"date_updated":"2026-03-16T10:59:16Z","date_published":"2026-03-01T00:00:00Z","ddc":["520"],"user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","OA_place":"publisher","file_date_updated":"2026-03-16T10:57:49Z","publication_identifier":{"issn":["0004-6361"],"eissn":["1432-0746"]},"intvolume":"       707","has_accepted_license":"1","oa":1,"author":[{"first_name":"Alberto","id":"018f0249-0e87-11f0-b167-cbce08fbd541","last_name":"Torralba Torregrosa","full_name":"Torralba Torregrosa, Alberto","orcid":"0000-0001-5586-6950"},{"orcid":"0000-0003-2871-127X","full_name":"Matthee, Jorryt J","first_name":"Jorryt J","last_name":"Matthee","id":"7439a258-f3c0-11ec-9501-9df22fe06720"},{"full_name":"Pezzulli, Gabriele","last_name":"Pezzulli","first_name":"Gabriele"},{"full_name":"Naidu, Rohan P.","last_name":"Naidu","first_name":"Rohan P."},{"full_name":"Ishikawa, Yuzo","last_name":"Ishikawa","first_name":"Yuzo"},{"last_name":"Brammer","first_name":"Gabriel B.","full_name":"Brammer, Gabriel B."},{"full_name":"Chang, Seok Jun","last_name":"Chang","first_name":"Seok Jun"},{"full_name":"Chisholm, John","first_name":"John","last_name":"Chisholm"},{"first_name":"Anna","last_name":"De Graaff","full_name":"De Graaff, Anna"},{"first_name":"Francesco","last_name":"D’Eugenio","full_name":"D’Eugenio, Francesco"},{"first_name":"Claudia","last_name":"Di Cesare","id":"2d002343-372f-11ef-98ec-a164d20427cb","full_name":"Di Cesare, Claudia"},{"first_name":"Anna Christina","last_name":"Eilers","full_name":"Eilers, Anna Christina"},{"last_name":"Greene","first_name":"Jenny E.","full_name":"Greene, Jenny E."},{"full_name":"Gronke, Max","last_name":"Gronke","first_name":"Max"},{"first_name":"Edoardo","id":"4053390a-6b68-11ef-9828-a3b8adef8d0a","last_name":"Iani","orcid":"0000-0001-8386-3546","full_name":"Iani, Edoardo"},{"full_name":"Kokorev, Vasily","first_name":"Vasily","last_name":"Kokorev"},{"full_name":"Kotiwale, Gauri","first_name":"Gauri","last_name":"Kotiwale","id":"1438afc8-1ff6-11ee-9fa6-cd4a75d66875"},{"first_name":"Ivan","id":"9a9394cb-3200-11ee-973b-f5ba2a8b16e4","last_name":"Kramarenko","full_name":"Kramarenko, Ivan","orcid":"0000-0001-5346-6048"},{"full_name":"Ma, Yilun","last_name":"Ma","first_name":"Yilun"},{"id":"edaf889c-c7cd-11ef-ab1b-bb28c431bd29","last_name":"Mascia","first_name":"Sara","full_name":"Mascia, Sara"},{"full_name":"Navarrete, Benjamín","last_name":"Navarrete","id":"aa14a535-50c9-11ef-b52e-e0c373d10148","first_name":"Benjamín"},{"last_name":"Nelson","first_name":"Erica","full_name":"Nelson, Erica"},{"first_name":"Pascal","last_name":"Oesch","full_name":"Oesch, Pascal"},{"full_name":"Simcoe, Robert A.","last_name":"Simcoe","first_name":"Robert A."},{"last_name":"Wuyts","first_name":"Stijn","full_name":"Wuyts, Stijn"}],"external_id":{"arxiv":["2510.00103"]},"month":"03","date_created":"2026-03-15T23:01:36Z","citation":{"short":"A. Torralba Torregrosa, J.J. Matthee, G. Pezzulli, R.P. Naidu, Y. Ishikawa, G.B. Brammer, S.J. Chang, J. Chisholm, A. De Graaff, F. D’Eugenio, C. Di Cesare, A.C. Eilers, J.E. Greene, M. Gronke, E. Iani, V. Kokorev, G. Kotiwale, I. Kramarenko, Y. Ma, S. Mascia, B. Navarrete, E. Nelson, P. Oesch, R.A. Simcoe, S. Wuyts, Astronomy &#38; Astrophysics 707 (2026).","apa":"Torralba Torregrosa, A., Matthee, J. J., Pezzulli, G., Naidu, R. P., Ishikawa, Y., Brammer, G. B., … Wuyts, S. (2026). The warm outer layer of a little red dot as the source of [Fe ii] and collisional Balmer lines with scattering wings. <i>Astronomy &#38; Astrophysics</i>. EDP Sciences. <a href=\"https://doi.org/10.1051/0004-6361/202557537\">https://doi.org/10.1051/0004-6361/202557537</a>","ama":"Torralba Torregrosa A, Matthee JJ, Pezzulli G, et al. The warm outer layer of a little red dot as the source of [Fe ii] and collisional Balmer lines with scattering wings. <i>Astronomy &#38; Astrophysics</i>. 2026;707. doi:<a href=\"https://doi.org/10.1051/0004-6361/202557537\">10.1051/0004-6361/202557537</a>","mla":"Torralba Torregrosa, Alberto, et al. “The Warm Outer Layer of a Little Red Dot as the Source of [Fe Ii] and Collisional Balmer Lines with Scattering Wings.” <i>Astronomy &#38; Astrophysics</i>, vol. 707, A75, EDP Sciences, 2026, doi:<a href=\"https://doi.org/10.1051/0004-6361/202557537\">10.1051/0004-6361/202557537</a>.","ieee":"A. Torralba Torregrosa <i>et al.</i>, “The warm outer layer of a little red dot as the source of [Fe ii] and collisional Balmer lines with scattering wings,” <i>Astronomy &#38; Astrophysics</i>, vol. 707. EDP Sciences, 2026.","ista":"Torralba Torregrosa A, Matthee JJ, Pezzulli G, Naidu RP, Ishikawa Y, Brammer GB, Chang SJ, Chisholm J, De Graaff A, D’Eugenio F, Di Cesare C, Eilers AC, Greene JE, Gronke M, Iani E, Kokorev V, Kotiwale G, Kramarenko I, Ma Y, Mascia S, Navarrete B, Nelson E, Oesch P, Simcoe RA, Wuyts S. 2026. The warm outer layer of a little red dot as the source of [Fe ii] and collisional Balmer lines with scattering wings. Astronomy &#38; Astrophysics. 707, A75.","chicago":"Torralba Torregrosa, Alberto, Jorryt J Matthee, Gabriele Pezzulli, Rohan P. Naidu, Yuzo Ishikawa, Gabriel B. Brammer, Seok Jun Chang, et al. “The Warm Outer Layer of a Little Red Dot as the Source of [Fe Ii] and Collisional Balmer Lines with Scattering Wings.” <i>Astronomy &#38; Astrophysics</i>. EDP Sciences, 2026. <a href=\"https://doi.org/10.1051/0004-6361/202557537\">https://doi.org/10.1051/0004-6361/202557537</a>."},"year":"2026","OA_type":"diamond","department":[{"_id":"JoMa"}],"status":"public"},{"date_published":"2026-03-01T00:00:00Z","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","ddc":["520"],"date_updated":"2026-03-16T10:52:44Z","OA_place":"publisher","file_date_updated":"2026-03-16T10:48:07Z","intvolume":"       707","publication_identifier":{"issn":["0004-6361"],"eissn":["1432-0746"]},"language":[{"iso":"eng"}],"_id":"21452","PlanS_conform":"1","day":"01","title":"The slope and scatter of the star-forming main sequence at z ∼ 5: Reconciling observations with simulations","arxiv":1,"date_created":"2026-03-15T23:01:36Z","citation":{"ista":"Di Cesare C, Matthee JJ, Naidu RP, Torralba A, Kotiwale G, Kramarenko I, Blaizot J, Rosdahl J, Leja J, Iani E, Adamo A, Covelo-Paz A, Furtak LJ, Heintz KE, Mascia S, Navarrete B, Oesch PA, Romano M, Shivaei I, Tacchella S. 2026. The slope and scatter of the star-forming main sequence at z ∼ 5: Reconciling observations with simulations. Astronomy &#38; Astrophysics. 707, A129.","chicago":"Di Cesare, Claudia, Jorryt J Matthee, Rohan P. Naidu, Alberto Torralba, Gauri Kotiwale, Ivan Kramarenko, Jeremy Blaizot, et al. “The Slope and Scatter of the Star-Forming Main Sequence at z ∼ 5: Reconciling Observations with Simulations.” <i>Astronomy &#38; Astrophysics</i>. EDP Sciences, 2026. <a href=\"https://doi.org/10.1051/0004-6361/202557790\">https://doi.org/10.1051/0004-6361/202557790</a>.","ieee":"C. Di Cesare <i>et al.</i>, “The slope and scatter of the star-forming main sequence at z ∼ 5: Reconciling observations with simulations,” <i>Astronomy &#38; Astrophysics</i>, vol. 707. EDP Sciences, 2026.","mla":"Di Cesare, Claudia, et al. “The Slope and Scatter of the Star-Forming Main Sequence at z ∼ 5: Reconciling Observations with Simulations.” <i>Astronomy &#38; Astrophysics</i>, vol. 707, A129, EDP Sciences, 2026, doi:<a href=\"https://doi.org/10.1051/0004-6361/202557790\">10.1051/0004-6361/202557790</a>.","ama":"Di Cesare C, Matthee JJ, Naidu RP, et al. The slope and scatter of the star-forming main sequence at z ∼ 5: Reconciling observations with simulations. <i>Astronomy &#38; Astrophysics</i>. 2026;707. doi:<a href=\"https://doi.org/10.1051/0004-6361/202557790\">10.1051/0004-6361/202557790</a>","short":"C. Di Cesare, J.J. Matthee, R.P. Naidu, A. Torralba, G. Kotiwale, I. Kramarenko, J. Blaizot, J. Rosdahl, J. Leja, E. Iani, A. Adamo, A. Covelo-Paz, L.J. Furtak, K.E. Heintz, S. Mascia, B. Navarrete, P.A. Oesch, M. Romano, I. Shivaei, S. Tacchella, Astronomy &#38; Astrophysics 707 (2026).","apa":"Di Cesare, C., Matthee, J. J., Naidu, R. P., Torralba, A., Kotiwale, G., Kramarenko, I., … Tacchella, S. (2026). The slope and scatter of the star-forming main sequence at z ∼ 5: Reconciling observations with simulations. <i>Astronomy &#38; Astrophysics</i>. EDP Sciences. <a href=\"https://doi.org/10.1051/0004-6361/202557790\">https://doi.org/10.1051/0004-6361/202557790</a>"},"year":"2026","OA_type":"diamond","department":[{"_id":"JoMa"},{"_id":"GradSch"}],"status":"public","oa":1,"has_accepted_license":"1","author":[{"first_name":"Claudia","last_name":"Di Cesare","id":"2d002343-372f-11ef-98ec-a164d20427cb","full_name":"Di Cesare, Claudia"},{"full_name":"Matthee, Jorryt J","orcid":"0000-0003-2871-127X","first_name":"Jorryt J","id":"7439a258-f3c0-11ec-9501-9df22fe06720","last_name":"Matthee"},{"last_name":"Naidu","first_name":"Rohan P.","full_name":"Naidu, Rohan P."},{"full_name":"Torralba, Alberto","first_name":"Alberto","last_name":"Torralba"},{"first_name":"Gauri","id":"1438afc8-1ff6-11ee-9fa6-cd4a75d66875","last_name":"Kotiwale","full_name":"Kotiwale, Gauri"},{"full_name":"Kramarenko, Ivan","orcid":"0000-0001-5346-6048","first_name":"Ivan","id":"9a9394cb-3200-11ee-973b-f5ba2a8b16e4","last_name":"Kramarenko"},{"first_name":"Jeremy","last_name":"Blaizot","full_name":"Blaizot, Jeremy"},{"last_name":"Rosdahl","first_name":"Joakim","full_name":"Rosdahl, Joakim"},{"full_name":"Leja, Joel","first_name":"Joel","last_name":"Leja"},{"last_name":"Iani","id":"4053390a-6b68-11ef-9828-a3b8adef8d0a","first_name":"Edoardo","full_name":"Iani, Edoardo","orcid":"0000-0001-8386-3546"},{"full_name":"Adamo, Angela","last_name":"Adamo","first_name":"Angela"},{"first_name":"Alba","last_name":"Covelo-Paz","full_name":"Covelo-Paz, Alba"},{"last_name":"Furtak","first_name":"Lukas J.","full_name":"Furtak, Lukas J."},{"last_name":"Heintz","first_name":"Kasper E.","full_name":"Heintz, Kasper E."},{"id":"edaf889c-c7cd-11ef-ab1b-bb28c431bd29","last_name":"Mascia","first_name":"Sara","full_name":"Mascia, Sara"},{"full_name":"Navarrete, Benjamín","id":"aa14a535-50c9-11ef-b52e-e0c373d10148","last_name":"Navarrete","first_name":"Benjamín"},{"first_name":"Pascal A.","last_name":"Oesch","full_name":"Oesch, Pascal A."},{"full_name":"Romano, Michael","last_name":"Romano","first_name":"Michael"},{"full_name":"Shivaei, Irene","last_name":"Shivaei","first_name":"Irene"},{"full_name":"Tacchella, Sandro","last_name":"Tacchella","first_name":"Sandro"}],"external_id":{"arxiv":["2510.19044"]},"month":"03","fulldoi":"https://doi.org/10.1051/0004-6361/202557790","type":"journal_article","DOAJ_listed":"1","tmp":{"name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","image":"/images/cc_by.png","short":"CC BY (4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode"},"publisher":"EDP Sciences","scopus_import":"1","corr_author":"1","publication_status":"published","oa_version":"Published Version","article_number":"A129","volume":707,"doi":"10.1051/0004-6361/202557790","acknowledgement":"We thank the anonymous referee for the insightful comments that helped improving the manuscript. We thank Romain. A. Meyer for valuable discussion, Pierluigi Rinaldi for his help with data handling and Luca Graziani and William McClymont for providing the dustyGadget and\r\nTHESAN-ZOOM data, respectively. Funded by the European Union (ERC, AGENTS, 101076224). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them. This work is based on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These observations are associated with program # 3516. We acknowledge funding from JWST program GO-3516. Software used in developing this work includes: matplotlib (Hunter 2007), numpy (Oliphant 2007), scipy (Virtanen et al. 2020), TOPCAT (Taylor 2005), and Astropy (Astropy Collaboration 2013).","file":[{"relation":"main_file","file_name":"2026_AstronomyAstrophysics_DiCesare.pdf","file_size":1821411,"checksum":"c056b00ce7324849754521fde10fb7ca","creator":"dernst","file_id":"21459","success":1,"content_type":"application/pdf","access_level":"open_access","date_updated":"2026-03-16T10:48:07Z","date_created":"2026-03-16T10:48:07Z"}],"publication":"Astronomy & Astrophysics","project":[{"grant_number":"101076224","name":"Young galaxies as tracers and agents of cosmic reionization","_id":"bd9b2118-d553-11ed-ba76-db24564edfea"}],"abstract":[{"text":"Galaxies exhibit a tight correlation between their star formation rate (SFR) and stellar mass over a wide redshift range known as the star-forming main sequence (SFMS). With JWST, the SFMS can now be investigated at high redshifts down to masses of ∼106 M⊙, using sensitive star formation rate tracers such as the Hα emission, which allow us to probe the variability in the star formation histories. We present inferences of the SFMS based on 316 Hα-selected galaxies at z ∼ 4 − 5 with log(M★/M⊙) = 6.4 − 10.6. These galaxies were identified behind the Abell 2744 lensing cluster with NIRCam grism spectroscopy from the survey All the Little Things (ALT). At face value, our data suggest a shallow slope in the SFMS (SFR ∝ M★α, with α = 0.45). After we corrected this for the Hα-flux limited nature of our survey using a Bayesian framework, the slope steepened to α = 0.59+0.10−0.09, whereas current data on their own are inconclusive on the mass dependence of the scatter. These slopes differ significantly from the slope of ∼1 that is expected from the observed evolution of the galaxy stellar mass function and from simulations. When we fixed the slope to α = 1, we found evidence for a decreasing intrinsic scatter with stellar mass (from ∼0.5 dex at M★ = 108 M⊙ to 0.4 dex at M★ = 1010 M⊙). This difference might be explained by a (combination of) luminosity-dependent SFR(Hα) calibration, a population of (mini)-quenched low-mass galaxies, or underestimated dust attenuation in high-mass galaxies. Future deep observations with different facilities can quantify these processes, which will enable us to achieve better insights into the variability of the star formation histories.","lang":"eng"}],"article_type":"original","quality_controlled":"1","article_processing_charge":"No"},{"intvolume":"       707","publication_identifier":{"eissn":["1432-0746"],"issn":["0004-6361"]},"file_date_updated":"2026-03-23T15:44:09Z","OA_place":"publisher","date_published":"2026-03-05T00:00:00Z","date_updated":"2026-03-23T15:46:31Z","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","ddc":["520"],"arxiv":1,"title":"H α as a tracer of star formation in the SPHINX cosmological simulations","day":"05","PlanS_conform":"1","_id":"21481","language":[{"iso":"eng"}],"status":"public","department":[{"_id":"JoMa"}],"OA_type":"diamond","year":"2026","date_created":"2026-03-23T14:58:03Z","citation":{"ista":"Kramarenko I, Rosdahl J, Blaizot J, Matthee JJ, Katz H, Di Cesare C. 2026. H α as a tracer of star formation in the SPHINX cosmological simulations. Astronomy &#38; Astrophysics. 707, A184.","chicago":"Kramarenko, Ivan, J. Rosdahl, J. Blaizot, Jorryt J Matthee, H. Katz, and Claudia Di Cesare. “H α as a Tracer of Star Formation in the SPHINX Cosmological Simulations.” <i>Astronomy &#38; Astrophysics</i>. EDP Sciences, 2026. <a href=\"https://doi.org/10.1051/0004-6361/202557114\">https://doi.org/10.1051/0004-6361/202557114</a>.","ieee":"I. Kramarenko, J. Rosdahl, J. Blaizot, J. J. Matthee, H. Katz, and C. Di Cesare, “H α as a tracer of star formation in the SPHINX cosmological simulations,” <i>Astronomy &#38; Astrophysics</i>, vol. 707. EDP Sciences, 2026.","ama":"Kramarenko I, Rosdahl J, Blaizot J, Matthee JJ, Katz H, Di Cesare C. H α as a tracer of star formation in the SPHINX cosmological simulations. <i>Astronomy &#38; Astrophysics</i>. 2026;707. doi:<a href=\"https://doi.org/10.1051/0004-6361/202557114\">10.1051/0004-6361/202557114</a>","short":"I. Kramarenko, J. Rosdahl, J. Blaizot, J.J. Matthee, H. Katz, C. Di Cesare, Astronomy &#38; Astrophysics 707 (2026).","apa":"Kramarenko, I., Rosdahl, J., Blaizot, J., Matthee, J. J., Katz, H., &#38; Di Cesare, C. (2026). H α as a tracer of star formation in the SPHINX cosmological simulations. <i>Astronomy &#38; Astrophysics</i>. EDP Sciences. <a href=\"https://doi.org/10.1051/0004-6361/202557114\">https://doi.org/10.1051/0004-6361/202557114</a>","mla":"Kramarenko, Ivan, et al. “H α as a Tracer of Star Formation in the SPHINX Cosmological Simulations.” <i>Astronomy &#38; Astrophysics</i>, vol. 707, A184, EDP Sciences, 2026, doi:<a href=\"https://doi.org/10.1051/0004-6361/202557114\">10.1051/0004-6361/202557114</a>."},"month":"03","external_id":{"arxiv":["2509.05403"]},"author":[{"full_name":"Kramarenko, Ivan","orcid":"0000-0001-5346-6048","first_name":"Ivan","last_name":"Kramarenko","id":"9a9394cb-3200-11ee-973b-f5ba2a8b16e4"},{"full_name":"Rosdahl, J.","last_name":"Rosdahl","first_name":"J."},{"first_name":"J.","last_name":"Blaizot","full_name":"Blaizot, J."},{"orcid":"0000-0003-2871-127X","full_name":"Matthee, Jorryt J","id":"7439a258-f3c0-11ec-9501-9df22fe06720","last_name":"Matthee","first_name":"Jorryt J"},{"full_name":"Katz, H.","first_name":"H.","last_name":"Katz"},{"full_name":"Di Cesare, Claudia","last_name":"Di Cesare","id":"2d002343-372f-11ef-98ec-a164d20427cb","first_name":"Claudia"}],"oa":1,"has_accepted_license":"1","publisher":"EDP Sciences","tmp":{"name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","image":"/images/cc_by.png","short":"CC BY (4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode"},"DOAJ_listed":"1","type":"journal_article","fulldoi":"https://doi.org/10.1051/0004-6361/202557114","volume":707,"article_number":"A184","oa_version":"Published Version","publication_status":"published","corr_author":"1","file":[{"content_type":"application/pdf","access_level":"open_access","date_updated":"2026-03-23T15:44:09Z","date_created":"2026-03-23T15:44:09Z","relation":"main_file","creator":"dernst","file_size":904565,"file_name":"2026_AstronomyAstrophysics_Kramarenko.pdf","checksum":"7429076b381dd498084f40ffd199e714","file_id":"21492","success":1}],"acknowledgement":"We thank the anonymous referee for the insightful comments that helped improve the manuscript. We also thank Thibault Garel, Pascal Oesch, Irene Shivaei, Charlotte Simmonds, Andrew Hopkins, Daniel Schaerer, and Rashmi Gottumukkala for useful comments and productive discussions. We gratefully acknowledge support from the CBPsmn (PSMN, Pôle Scientifique de Modélisation Numérique) of the ENS de Lyon for the computing resources.\r\nFunded by the European Union (ERC, AGENTS, 101076224). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them. This work made extensive use of several open-source software packages, and we gratefully acknowledge the efforts of their authors: numpy (Harris et al. 2020), astropy (Astropy Collaboration 2022), matplotlib (Hunter 2007), ipython (Perez & Granger 2007), and scikit-learn (Pedregosa et al. 2011).","doi":"10.1051/0004-6361/202557114","article_processing_charge":"No","quality_controlled":"1","article_type":"original","abstract":[{"text":"The Hα emission line in galaxies is a powerful tracer of their recent star formation activity. With the advent of JWST, we are now able to routinely observe Hα in galaxies at high redshift (z ≳ 3) and thus measure their star formation rates (SFRs). However, using classical SFR(Hα) calibrations to derive the SFRs leads to biased results because high-redshift galaxies are commonly characterized by low metallicities and bursty star formation histories, affecting the conversion factor between the Hα luminosity (LHα) and the SFR. We developed a set of new SFR(Hα) calibrations that allowed us to predict the SFRs of Hα-emitters at z ≳ 3 with very little error. We used the SPHINX cosmological simulations to select a sample of star-forming galaxies representative of the Hα-emitter population observed with JWST. We then derived linear corrections to the classical SFR(Hα) calibrations that took variations in the physical properties (e.g., stellar metallicities) among individual galaxies into account. We obtained two new SFR(Hα) calibrations that compared to the classical calibrations reduce the root mean squared error (RMSE) in the predicted SFRs by ΔRMSE ≈ 0.04 dex and ΔRMSE ≈ 0.06 dex, respectively. Using the recent JWST NIRCam/grism observations of Hα-emitters at z ∼ 6, we show that the new calibrations affect the high-redshift galaxy population statistics: (i) the estimated cosmic SFR density decreases by ΔρSFR ≈ 12%, and (ii) the observed slope of the star formation main sequence increases by Δ∂logSFR/∂logM★ = 0.08 ± 0.02.","lang":"eng"}],"project":[{"name":"Young galaxies as tracers and agents of cosmic reionization","grant_number":"101076224","_id":"bd9b2118-d553-11ed-ba76-db24564edfea"}],"publication":"Astronomy & Astrophysics"},{"language":[{"iso":"eng"}],"_id":"21709","issue":"1","day":"20","title":"The X-ray dot: Exotic dust or a late-stage Little Red Dot?","arxiv":1,"date_published":"2026-03-20T00:00:00Z","date_updated":"2026-05-04T07:13:07Z","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","ddc":["520"],"OA_place":"publisher","publication_identifier":{"eissn":["2041-8213"],"issn":["2041-8205"]},"intvolume":"      1000","file_date_updated":"2026-05-04T07:11:37Z","has_accepted_license":"1","oa":1,"author":[{"full_name":"Hviding, Raphael E.","last_name":"Hviding","first_name":"Raphael E."},{"full_name":"De Graaff, Anna","last_name":"De Graaff","first_name":"Anna"},{"last_name":"Liu","first_name":"Hanpu","full_name":"Liu, Hanpu"},{"last_name":"Goulding","first_name":"Andy D.","full_name":"Goulding, Andy D."},{"full_name":"Ma, Yilun","first_name":"Yilun","last_name":"Ma"},{"full_name":"Greene, Jenny E.","last_name":"Greene","first_name":"Jenny E."},{"full_name":"Boogaard, Leindert A.","first_name":"Leindert A.","last_name":"Boogaard"},{"last_name":"Bunker","first_name":"Andrew J.","full_name":"Bunker, Andrew J."},{"last_name":"Cleri","first_name":"Nikko J.","full_name":"Cleri, Nikko J."},{"full_name":"Franx, Marijn","first_name":"Marijn","last_name":"Franx"},{"first_name":"Michaela","last_name":"Hirschmann","full_name":"Hirschmann, Michaela"},{"full_name":"Leja, Joel","last_name":"Leja","first_name":"Joel"},{"last_name":"Matthee","id":"7439a258-f3c0-11ec-9501-9df22fe06720","first_name":"Jorryt J","orcid":"0000-0003-2871-127X","full_name":"Matthee, Jorryt J"},{"full_name":"Naidu, Rohan P.","last_name":"Naidu","first_name":"Rohan P."},{"full_name":"Setton, David J.","last_name":"Setton","first_name":"David J."},{"full_name":"Übler, Hannah","last_name":"Übler","first_name":"Hannah"},{"full_name":"Venturi, Giacomo","last_name":"Venturi","first_name":"Giacomo"},{"full_name":"Wang, Bingjie","first_name":"Bingjie","last_name":"Wang"}],"external_id":{"arxiv":["2601.09778"]},"month":"03","year":"2026","OA_type":"gold","date_created":"2026-04-12T22:01:48Z","citation":{"ista":"Hviding RE, De Graaff A, Liu H, Goulding AD, Ma Y, Greene JE, Boogaard LA, Bunker AJ, Cleri NJ, Franx M, Hirschmann M, Leja J, Matthee JJ, Naidu RP, Setton DJ, Übler H, Venturi G, Wang B. 2026. The X-ray dot: Exotic dust or a late-stage Little Red Dot? The Astrophysical Journal Letters. 1000(1), L18.","chicago":"Hviding, Raphael E., Anna De Graaff, Hanpu Liu, Andy D. Goulding, Yilun Ma, Jenny E. Greene, Leindert A. Boogaard, et al. “The X-Ray Dot: Exotic Dust or a Late-Stage Little Red Dot?” <i>The Astrophysical Journal Letters</i>. IOP Publishing, 2026. <a href=\"https://doi.org/10.3847/2041-8213/ae4c88\">https://doi.org/10.3847/2041-8213/ae4c88</a>.","ieee":"R. E. Hviding <i>et al.</i>, “The X-ray dot: Exotic dust or a late-stage Little Red Dot?,” <i>The Astrophysical Journal Letters</i>, vol. 1000, no. 1. IOP Publishing, 2026.","ama":"Hviding RE, De Graaff A, Liu H, et al. The X-ray dot: Exotic dust or a late-stage Little Red Dot? <i>The Astrophysical Journal Letters</i>. 2026;1000(1). doi:<a href=\"https://doi.org/10.3847/2041-8213/ae4c88\">10.3847/2041-8213/ae4c88</a>","short":"R.E. Hviding, A. De Graaff, H. Liu, A.D. Goulding, Y. Ma, J.E. Greene, L.A. Boogaard, A.J. Bunker, N.J. Cleri, M. Franx, M. Hirschmann, J. Leja, J.J. Matthee, R.P. Naidu, D.J. Setton, H. Übler, G. Venturi, B. Wang, The Astrophysical Journal Letters 1000 (2026).","apa":"Hviding, R. E., De Graaff, A., Liu, H., Goulding, A. D., Ma, Y., Greene, J. E., … Wang, B. (2026). The X-ray dot: Exotic dust or a late-stage Little Red Dot? <i>The Astrophysical Journal Letters</i>. IOP Publishing. <a href=\"https://doi.org/10.3847/2041-8213/ae4c88\">https://doi.org/10.3847/2041-8213/ae4c88</a>","mla":"Hviding, Raphael E., et al. “The X-Ray Dot: Exotic Dust or a Late-Stage Little Red Dot?” <i>The Astrophysical Journal Letters</i>, vol. 1000, no. 1, L18, IOP Publishing, 2026, doi:<a href=\"https://doi.org/10.3847/2041-8213/ae4c88\">10.3847/2041-8213/ae4c88</a>."},"department":[{"_id":"JoMa"}],"status":"public","oa_version":"Published Version","publication_status":"published","volume":1000,"article_number":"L18","DOAJ_listed":"1","type":"journal_article","fulldoi":"https://doi.org/10.3847/2041-8213/ae4c88","publisher":"IOP Publishing","tmp":{"name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","image":"/images/cc_by.png","short":"CC BY (4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode"},"scopus_import":"1","publication":"The Astrophysical Journal Letters","abstract":[{"lang":"eng","text":"JWST’s “little red dots” (LRDs) are increasingly interpreted as active galactic nuclei (AGN) obscured by dense thermalized gas rather than dust as evidenced by their X-ray weakness, blackbody-like continua, and Balmer line profiles. Key questions are how LRDs connect to standard UV-luminous AGN, whether transitional phases exist, and whether they are observable. We present the “X-ray dot” (XRD), a compact source at z = 3.28 observed by the NIRSpec Wide Guaranteed Time Observation survey. The XRD exhibits LRD hallmarks: a blackbody-like (Teff ≃ 6400 K) red continuum, a faint but blue rest-UV excess, falling mid-IR emission, and broad Balmer lines (FWHM ∼ 2700–3200 km s−1). Unlike LRDs, however, it is remarkably X-ray luminous (L2−10 keV = 1044.18 erg s−1) and has a continuum inflection that is blueward of the Balmer limit. We find that the red rest-optical and blue mid-IR continuum cannot be reproduced by standard dust-attenuated AGN models without invoking extremely steep extinction curves, nor can the weak mid-IR emission be reconciled with well-established X-ray–torus scaling relations. We therefore consider an alternative scenario: the XRD may be an LRD in transition, where the gas envelope dominates the optical continuum but optically thin sight lines allow X-rays to escape. The XRD may thus provide a physical link between LRDs and standard AGN, offering direct evidence that LRDs are powered by supermassive black holes and providing insight into their accretion properties."}],"article_type":"original","quality_controlled":"1","article_processing_charge":"Yes","doi":"10.3847/2041-8213/ae4c88","acknowledgement":"We would like to thank the anonymous reviewer for their constructive comments, which improved the final manuscript.\r\n\r\nWe thank Bernd Husemann for his critical contributions to the NIRSpec Wide GTO survey, and in particular his help in selecting high-priority X-ray-luminous targets.\r\n\r\nR.E.H. acknowledges support by the German Aerospace Center (DLR) and the Federal Ministry for Economic Affairs and Energy (BMWi) through program 50OR2403 “RUBIES.” A.d.G. acknowledges support from a Clay Fellowship awarded by the Smithsonian Astrophysical Observatory. A.J.B. acknowledges funding from the “FirstGalaxies” Advanced grant from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement No. 789056). R.P.N. thanks Neil Pappalardo and Jane Pappalardo for their generous support of the MIT Pappalardo Fellowships in Physics. Support for this work was provided by the Brinson Foundation through a Brinson Prize Fellowship grant. H.Ü. acknowledges funding by the European Union (ERC APEX, 101164796). Views and opinions expressed are, however, those of the authors only and do not necessarily reflect those of the European Union or the European Research Council Executive Agency. Neither the European Union nor the granting authority can be held responsible for them. G.V. acknowledges support from European Union’s HE ERC Starting grant No. 101040227—WINGS. B.W. acknowledges support provided by NASA through Hubble Fellowship grant HST-HF2-51592.001 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, In., for NASA, under the contract NAS 5-26555.\r\n\r\nThe data products presented herein were retrieved from the Dawn JWST Archive (DJA). DJA is an initiative of the Cosmic Dawn Center (DAWN).\r\n\r\nThis work is based in part on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These observations are associated with programs Nos. GTO-1213. The data described here may be obtained from the MAST archive at DOI: 10.17909/qffz-b324.\r\n\r\nThis Letter employs a list of Chandra datasets, obtained by the Chandra X-ray Observatory, contained in DOI: 10.25574/cdc.540.\r\n\r\nThis work is based on observations taken by the 3D-HST Treasury Program (GO 12177 and 12328) with the NASA/ESA HST, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.\r\n\r\nThis work makes use of color palettes created by Martin Krzywinski designed for colorblindness. The color palettes and more information can be found at http://mkweb.bcgsc.ca/colorblind/.\r\n\r\nFacilities: CXO - Chandra X-ray Observatory satellite (ACIS), HST - Hubble Space Telescope satellite (ACS, WFC3) - , CFHT - Canada-France-Hawaii Telescope (WIRCam), JWST - James Webb Space Telescope (NIRSpec), Spitzer - Spitzer Space Telescope satellite (IRAC, MIPS) - , JCMT - James Clerk Maxwell Telescope (SCUBA).\r\n\r\nSoftware: Astropy (Astropy Collaboration et al. 2013, 2018, 2022), dust_attenuation, dust_extinction (K. Gordon 2024), jax (J. Bradbury et al. 2018), LaTeX (L. Lamport 1994), Matplotlib (J. D. Hunter 2007), NumPy (T. E. Oliphant 2006; S. van der Walt et al. 2011; C. R. Harris et al. 2020), NumPyro (D. Phan et al. 2019), scipy (P. Virtanen et al. 2020), sedpy (B. Johnson & J. Leja 2017), specutils (Astropy-Specutils Development Team 2019), unite (R. E. Hviding 2025).","file":[{"date_created":"2026-05-04T07:11:37Z","date_updated":"2026-05-04T07:11:37Z","content_type":"application/pdf","access_level":"open_access","creator":"dernst","checksum":"1be4f361bf59aa08b8c98ed4f475a463","file_name":"2026_AstrophysicalJourLetters_Hviding.pdf","file_size":2821786,"file_id":"21784","success":1,"relation":"main_file"}]},{"publication_identifier":{"eissn":["1538-4357"],"issn":["0004-637X"]},"intvolume":"       996","file_date_updated":"2026-05-04T11:19:48Z","OA_place":"publisher","date_updated":"2026-05-04T11:20:42Z","ddc":["520"],"user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","date_published":"2026-01-10T00:00:00Z","arxiv":1,"title":"What you see is what you get: Empirically measured bolometric luminosities of Little Red Dots","issue":"2","PlanS_conform":"1","day":"10","_id":"21715","language":[{"iso":"eng"}],"status":"public","department":[{"_id":"JoMa"}],"year":"2026","OA_type":"gold","date_created":"2026-04-12T22:01:50Z","citation":{"mla":"Greene, Jenny E., et al. “What You See Is What You Get: Empirically Measured Bolometric Luminosities of Little Red Dots.” <i>The Astrophysical Journal</i>, vol. 996, no. 2, 129, IOP Publishing, 2026, doi:<a href=\"https://doi.org/10.3847/1538-4357/ae1836\">10.3847/1538-4357/ae1836</a>.","ama":"Greene JE, Setton DJ, Furtak LJ, et al. What you see is what you get: Empirically measured bolometric luminosities of Little Red Dots. <i>The Astrophysical Journal</i>. 2026;996(2). doi:<a href=\"https://doi.org/10.3847/1538-4357/ae1836\">10.3847/1538-4357/ae1836</a>","short":"J.E. Greene, D.J. Setton, L.J. Furtak, R.P. Naidu, M. Volonteri, P. Dayal, I. Labbe, P. Van Dokkum, R. Bezanson, G. Brammer, S.E. Cutler, K. Glazebrook, A. De Graaff, M. Hirschmann, R.E. Hviding, V. Kokorev, J. Leja, H. Liu, Y. Ma, J.J. Matthee, T. Nanayakkara, P.A. Oesch, R. Pan, S.H. Price, J.S. Spilker, B. Wang, J.R. Weaver, K.E. Whitaker, C.C. Williams, A. Zitrin, The Astrophysical Journal 996 (2026).","apa":"Greene, J. E., Setton, D. J., Furtak, L. J., Naidu, R. P., Volonteri, M., Dayal, P., … Zitrin, A. (2026). What you see is what you get: Empirically measured bolometric luminosities of Little Red Dots. <i>The Astrophysical Journal</i>. IOP Publishing. <a href=\"https://doi.org/10.3847/1538-4357/ae1836\">https://doi.org/10.3847/1538-4357/ae1836</a>","ista":"Greene JE, Setton DJ, Furtak LJ, Naidu RP, Volonteri M, Dayal P, Labbe I, Van Dokkum P, Bezanson R, Brammer G, Cutler SE, Glazebrook K, De Graaff A, Hirschmann M, Hviding RE, Kokorev V, Leja J, Liu H, Ma Y, Matthee JJ, Nanayakkara T, Oesch PA, Pan R, Price SH, Spilker JS, Wang B, Weaver JR, Whitaker KE, Williams CC, Zitrin A. 2026. What you see is what you get: Empirically measured bolometric luminosities of Little Red Dots. The Astrophysical Journal. 996(2), 129.","chicago":"Greene, Jenny E., David J. Setton, Lukas J. Furtak, Rohan P. Naidu, Marta Volonteri, Pratika Dayal, Ivo Labbe, et al. “What You See Is What You Get: Empirically Measured Bolometric Luminosities of Little Red Dots.” <i>The Astrophysical Journal</i>. IOP Publishing, 2026. <a href=\"https://doi.org/10.3847/1538-4357/ae1836\">https://doi.org/10.3847/1538-4357/ae1836</a>.","ieee":"J. E. Greene <i>et al.</i>, “What you see is what you get: Empirically measured bolometric luminosities of Little Red Dots,” <i>The Astrophysical Journal</i>, vol. 996, no. 2. IOP Publishing, 2026."},"month":"01","external_id":{"arxiv":["2509.05434"]},"author":[{"full_name":"Greene, Jenny E.","first_name":"Jenny E.","last_name":"Greene"},{"full_name":"Setton, David J.","last_name":"Setton","first_name":"David J."},{"full_name":"Furtak, Lukas J.","last_name":"Furtak","first_name":"Lukas J."},{"full_name":"Naidu, Rohan P.","last_name":"Naidu","first_name":"Rohan P."},{"full_name":"Volonteri, Marta","last_name":"Volonteri","first_name":"Marta"},{"first_name":"Pratika","last_name":"Dayal","full_name":"Dayal, Pratika"},{"full_name":"Labbe, Ivo","first_name":"Ivo","last_name":"Labbe"},{"first_name":"Pieter","last_name":"Van Dokkum","full_name":"Van Dokkum, Pieter"},{"full_name":"Bezanson, Rachel","first_name":"Rachel","last_name":"Bezanson"},{"last_name":"Brammer","first_name":"Gabriel","full_name":"Brammer, Gabriel"},{"full_name":"Cutler, Sam E.","first_name":"Sam E.","last_name":"Cutler"},{"full_name":"Glazebrook, Karl","last_name":"Glazebrook","first_name":"Karl"},{"full_name":"De Graaff, Anna","first_name":"Anna","last_name":"De Graaff"},{"first_name":"Michaela","last_name":"Hirschmann","full_name":"Hirschmann, Michaela"},{"full_name":"Hviding, Raphael E.","last_name":"Hviding","first_name":"Raphael E."},{"first_name":"Vasily","last_name":"Kokorev","full_name":"Kokorev, Vasily"},{"first_name":"Joel","last_name":"Leja","full_name":"Leja, Joel"},{"full_name":"Liu, Hanpu","first_name":"Hanpu","last_name":"Liu"},{"first_name":"Yilun","last_name":"Ma","full_name":"Ma, Yilun"},{"full_name":"Matthee, Jorryt J","orcid":"0000-0003-2871-127X","first_name":"Jorryt J","id":"7439a258-f3c0-11ec-9501-9df22fe06720","last_name":"Matthee"},{"last_name":"Nanayakkara","first_name":"Themiya","full_name":"Nanayakkara, Themiya"},{"first_name":"Pascal A.","last_name":"Oesch","full_name":"Oesch, Pascal A."},{"full_name":"Pan, Richard","first_name":"Richard","last_name":"Pan"},{"first_name":"Sedona H.","last_name":"Price","full_name":"Price, Sedona H."},{"last_name":"Spilker","first_name":"Justin S.","full_name":"Spilker, Justin S."},{"full_name":"Wang, Bingjie","first_name":"Bingjie","last_name":"Wang"},{"first_name":"John R.","last_name":"Weaver","full_name":"Weaver, John R."},{"full_name":"Whitaker, Katherine E.","first_name":"Katherine E.","last_name":"Whitaker"},{"full_name":"Williams, Christina C.","first_name":"Christina C.","last_name":"Williams"},{"full_name":"Zitrin, Adi","last_name":"Zitrin","first_name":"Adi"}],"has_accepted_license":"1","oa":1,"scopus_import":"1","publisher":"IOP Publishing","tmp":{"name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","image":"/images/cc_by.png","short":"CC BY (4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode"},"DOAJ_listed":"1","type":"journal_article","fulldoi":"https://doi.org/10.3847/1538-4357/ae1836","volume":996,"article_number":"129","oa_version":"Published Version","publication_status":"published","file":[{"date_created":"2026-05-04T11:19:48Z","date_updated":"2026-05-04T11:19:48Z","content_type":"application/pdf","access_level":"open_access","file_name":"2026_AstrophysicalJour_Greene.pdf","creator":"dernst","checksum":"7b3cb025d4bcaa35c6e52bd0c8fb6cf4","file_size":684400,"file_id":"21792","success":1,"relation":"main_file"}],"acknowledgement":"We benefit from the following JWST programs: UNCOVER (JWST/GO #2561; Labbé & Bezanson); ALT (JWST-GO #3516; Naidu & Matthee); MegaScience (JWST-GO #4111; Suess); RUBIES (JWST-GO #4233; de Graaff & Brammer); PRIMER (JWST/GO #1837; Dunlop).\r\n\r\nWe acknowledge funding from NSF/AAG #2306950, JWST-GO-02561, JWST-GO-03516, and JWST-GO-04111, provided through a grant from the STScI under NASA contract NAS5-03127. I.L. acknowledges support from Australian Research Council Future Fellowship FT220100798. K.G. and T.N. acknowledge support from Australian Research Council Laureate Fellowship FL180100060. A.Z. acknowledges support by grant No. 2020750 from the United States-Israel Binational Science Foundation (BSF) and grant No. 2109066 from the United States National Science Foundation (NSF); by the Ministry of Science & Technology, Israel; and by the Israel Science Foundation grant No. 864/23. J.M. and I.K. are funded by the European Union (ERC, AGENTS, 101076224). Views and opinions expressed are, however, those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them. Y.F. acknowledges support from JSPS KAKENHI grant No. JSPS KAKENHI grant Nos. JP22K21349 and JP23K13149. This work has received funding from the Swiss State Secretariat for Education, Research and Innovation (SERI) under contract No. MB22.00072, as well as from the Swiss National Science Foundation (SNSF) through project grant 200020_207349. The Cosmic Dawn Center (DAWN) is funded by the Danish National Research Foundation under grant DNRF140. Support for this work for RPN was provided by NASA through the NASA Hubble Fellowship grant HST-HF2-51515.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. The work of CCW is supported by NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. J.M. acknowledges funding by the European Union (ERC, AGENTS, 101076224). R.E.H. acknowledges support by the German Aerospace Center (DLR) and the Federal Ministry for Economic Affairs and Energy (BMWi) through program 50OR2403 “RUBIES.”","doi":"10.3847/1538-4357/ae1836","article_processing_charge":"Yes","quality_controlled":"1","abstract":[{"lang":"eng","text":"New populations of red active galactic nuclei (known as “little red dots”) discovered by JWST exhibit remarkable spectral energy distributions. Leveraging X-ray through far-infrared observations of two of the most luminous known little red dots, we directly measure their bolometric luminosities. We find evidence that more than half of the bolometric luminosity likely emerges in the rest-frame optical, with Lbol/L5100 = 5, roughly half the value for “standard” active galactic nuclei. Meanwhile, the X-ray emitting corona, UV-emitting blackbody, and reprocessed mid to far-infrared emission are all considerably subdominant, assuming that the far-infrared luminosity is well below current measured limits. We present new bolometric corrections that dramatically lower inferred bolometric luminosities by a factor of 10 compared to published values in the literature. These bolometric corrections are in accord with expectations from models in which gas absorption and reprocessing are responsible for the red rest-frame optical colors of little red dots. We discuss how this lowered luminosity scale suggests a lower mass scale for the population by at least an order of magnitude (e.g., ∼105–107 M⊙ black holes, and ∼108 M⊙ galaxies), alleviating tensions with clustering, overmassive black holes, and the integrated black hole mass density in the Universe."}],"article_type":"original","publication":"The Astrophysical Journal","project":[{"_id":"bd9b2118-d553-11ed-ba76-db24564edfea","grant_number":"101076224","name":"Young galaxies as tracers and agents of cosmic reionization"}]},{"external_id":{"arxiv":["2602.02702"]},"month":"04","has_accepted_license":"1","oa":1,"author":[{"last_name":"Baggen","first_name":"Josephine F.W.","full_name":"Baggen, Josephine F.W."},{"first_name":"Matthew T.","last_name":"Scoggins","full_name":"Scoggins, Matthew T."},{"last_name":"Van Dokkum","first_name":"Pieter","full_name":"Van Dokkum, Pieter"},{"orcid":"0000-0003-3633-5403","full_name":"Haiman, Zoltán","first_name":"Zoltán","id":"7c006e8c-cc0d-11ee-8322-cb904ef76f36","last_name":"Haiman"},{"first_name":"Alberto","id":"018f0249-0e87-11f0-b167-cbce08fbd541","last_name":"Torralba Torregrosa","orcid":"0000-0001-5586-6950","full_name":"Torralba Torregrosa, Alberto"},{"orcid":"0000-0003-2871-127X","full_name":"Matthee, Jorryt J","id":"7439a258-f3c0-11ec-9501-9df22fe06720","last_name":"Matthee","first_name":"Jorryt J"}],"status":"public","citation":{"ista":"Baggen JFW, Scoggins MT, Van Dokkum P, Haiman Z, Torralba Torregrosa A, Matthee JJ. 2026. Connecting the dots: UV-bright companions of Little Red Dots as Lyman–Werner sources enabling direct-collapse Black Hole formation. The Astrophysical Journal Letters. 1002(1), L4.","chicago":"Baggen, Josephine F.W., Matthew T. Scoggins, Pieter Van Dokkum, Zoltán Haiman, Alberto Torralba Torregrosa, and Jorryt J Matthee. “Connecting the Dots: UV-Bright Companions of Little Red Dots as Lyman–Werner Sources Enabling Direct-Collapse Black Hole Formation.” <i>The Astrophysical Journal Letters</i>. IOP Publishing, 2026. <a href=\"https://doi.org/10.3847/2041-8213/ae58a5\">https://doi.org/10.3847/2041-8213/ae58a5</a>.","ieee":"J. F. W. Baggen, M. T. Scoggins, P. Van Dokkum, Z. Haiman, A. Torralba Torregrosa, and J. J. Matthee, “Connecting the dots: UV-bright companions of Little Red Dots as Lyman–Werner sources enabling direct-collapse Black Hole formation,” <i>The Astrophysical Journal Letters</i>, vol. 1002, no. 1. IOP Publishing, 2026.","mla":"Baggen, Josephine F. W., et al. “Connecting the Dots: UV-Bright Companions of Little Red Dots as Lyman–Werner Sources Enabling Direct-Collapse Black Hole Formation.” <i>The Astrophysical Journal Letters</i>, vol. 1002, no. 1, L4, IOP Publishing, 2026, doi:<a href=\"https://doi.org/10.3847/2041-8213/ae58a5\">10.3847/2041-8213/ae58a5</a>.","ama":"Baggen JFW, Scoggins MT, Van Dokkum P, Haiman Z, Torralba Torregrosa A, Matthee JJ. Connecting the dots: UV-bright companions of Little Red Dots as Lyman–Werner sources enabling direct-collapse Black Hole formation. <i>The Astrophysical Journal Letters</i>. 2026;1002(1). doi:<a href=\"https://doi.org/10.3847/2041-8213/ae58a5\">10.3847/2041-8213/ae58a5</a>","apa":"Baggen, J. F. W., Scoggins, M. T., Van Dokkum, P., Haiman, Z., Torralba Torregrosa, A., &#38; Matthee, J. J. (2026). Connecting the dots: UV-bright companions of Little Red Dots as Lyman–Werner sources enabling direct-collapse Black Hole formation. <i>The Astrophysical Journal Letters</i>. IOP Publishing. <a href=\"https://doi.org/10.3847/2041-8213/ae58a5\">https://doi.org/10.3847/2041-8213/ae58a5</a>","short":"J.F.W. Baggen, M.T. Scoggins, P. Van Dokkum, Z. Haiman, A. Torralba Torregrosa, J.J. Matthee, The Astrophysical Journal Letters 1002 (2026)."},"date_created":"2026-05-10T22:02:15Z","year":"2026","OA_type":"gold","department":[{"_id":"ZoHa"},{"_id":"JoMa"}],"title":"Connecting the dots: UV-bright companions of Little Red Dots as Lyman–Werner sources enabling direct-collapse Black Hole formation","arxiv":1,"language":[{"iso":"eng"}],"_id":"21846","PlanS_conform":"1","day":"10","issue":"1","OA_place":"publisher","file_date_updated":"2026-05-11T06:44:37Z","intvolume":"      1002","publication_identifier":{"eissn":["2041-8213"],"issn":["2041-8205"]},"user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","date_updated":"2026-05-11T06:48:33Z","date_published":"2026-04-10T00:00:00Z","ddc":["520"],"quality_controlled":"1","article_processing_charge":"Yes","publication":"The Astrophysical Journal Letters","project":[{"name":"Young galaxies as tracers and agents of cosmic reionization","grant_number":"101076224","_id":"bd9b2118-d553-11ed-ba76-db24564edfea"}],"article_type":"original","abstract":[{"lang":"eng","text":"We compile a sample of 83 little red dots (LRDs) with JWST imaging and find that a substantial fraction (∼43%, rising to ≳80% for the most luminous LRDs) host one or more spatially offset, UV-bright companions at projected separations of 0.5 kpc ≲ d ≲ 5 kpc, with median 〈d〉 = 1.0 kpc. This fraction is even higher when smaller spatial scales are probed at high signal-to-noise ratio: the two most strongly lensed LRDs, A383-LRD1 and the newly discovered A68-LRD1, both have UV-bright companions at separations of only d ∼ 0.3 kpc, below the resolution limit of most unlensed JWST samples. We explore whether these ubiquitous red/blue configurations may be physically linked to the formation of LRDs, in analogy with the “synchronized pair” scenario originally proposed for direct-collapse black hole formation. In this picture, UV radiation from the companions, with typically modest stellar masses (M∗ ∼ 108−109 M⊙), suppresses molecular hydrogen cooling in nearby gas, allowing nearly isothermal collapse and the formation of extremely compact objects, such as massive black holes, supermassive stars, or quasi-stars. Using component-resolved photometry and spectral energy distribution modeling, we infer Lyman–Werner radiation fields of J21,LW ∼ 102.5–105 at the locations of the red components, comparable to those required in direct-collapse models, suggesting that the necessary photodissociation conditions are realized in many LRD systems. This framework provides a simple and self-consistent explanation for the extreme compactness and distinctive spectral properties of LRDs and links long-standing theoretical models for early compact object formation directly to a population now observed with JWST in the early Universe."}],"file":[{"date_created":"2026-05-11T06:44:37Z","date_updated":"2026-05-11T06:44:37Z","content_type":"application/pdf","access_level":"open_access","checksum":"8c31d8603cd6ad39c772a72d136dc3f8","creator":"dernst","file_name":"2026_AstrophysicalJourLetters_Baggen.pdf","file_size":13359642,"success":1,"file_id":"21851","relation":"main_file"}],"doi":"10.3847/2041-8213/ae58a5","acknowledgement":"We thank Earl Bellinger, Fabio Pacucci, Andrea Ferrara, and Dale Kocevski for useful discussions. This work is based on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These imaging observations are associated with programs 1345, 1180, 1181, 1243, 6882, 2561, 1324, 4111, and 1895. The compiled dataset can be accessed at doi:10.17909/1m8f-9c47. The Cosmic Dawn Center (DAWN) is funded by the Danish National Research Foundation under grant DNRF140. J.M. and A.T. acknowledge funding by the European Union (ERC, AGENTS, 101076224). This work was performed in part at Aspen Center for Physics, which is supported by National Science Foundation grant PHY-2210452. This work used the following Python packages: Matplotlib (J. D. Hunter 2007), SciPy (P. Virtanen et al. 2020), NumPy (S. van der Walt et al. 2011), AstroPy (Astropy Collaboration et al. 2022), colossus (B. Diemer 2018), and photutils (L. Bradley et al. 2025).","article_number":"L4","volume":1002,"publication_status":"published","oa_version":"Published Version","tmp":{"name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","image":"/images/cc_by.png","short":"CC BY (4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode"},"publisher":"IOP Publishing","scopus_import":"1","fulldoi":"https://doi.org/10.3847/2041-8213/ae58a5","type":"journal_article","DOAJ_listed":"1"},{"has_accepted_license":"1","oa":1,"author":[{"last_name":"Wang","first_name":"Bingjie","full_name":"Wang, Bingjie"},{"full_name":"Leja, Joel","last_name":"Leja","first_name":"Joel"},{"full_name":"Katz, Harley","last_name":"Katz","first_name":"Harley"},{"last_name":"Inayoshi","first_name":"Kohei","full_name":"Inayoshi, Kohei"},{"full_name":"Cleri, Nikko J.","last_name":"Cleri","first_name":"Nikko J."},{"first_name":"Anna","last_name":"De Graaff","full_name":"De Graaff, Anna"},{"first_name":"Raphael E.","last_name":"Hviding","full_name":"Hviding, Raphael E."},{"full_name":"Van Dokkum, Pieter","last_name":"Van Dokkum","first_name":"Pieter"},{"last_name":"Greene","first_name":"Jenny E.","full_name":"Greene, Jenny E."},{"last_name":"Labbé","first_name":"Ivo","full_name":"Labbé, Ivo"},{"orcid":"0000-0003-2871-127X","full_name":"Matthee, Jorryt J","id":"7439a258-f3c0-11ec-9501-9df22fe06720","last_name":"Matthee","first_name":"Jorryt J"},{"first_name":"Ian","last_name":"Mcconachie","full_name":"Mcconachie, Ian"},{"full_name":"Naidu, Rohan P.","last_name":"Naidu","first_name":"Rohan P."},{"last_name":"Nelson","first_name":"Erica J.","full_name":"Nelson, Erica J."}],"external_id":{"arxiv":["2508.18358"]},"month":"05","date_created":"2026-05-17T22:02:10Z","citation":{"ieee":"B. Wang <i>et al.</i>, “The missing hard photons of Little Red Dots: Their incident ionizing spectra resemble massive stars,” <i>The Astrophysical Journal</i>, vol. 1003, no. 1. IOP Publishing, 2026.","ista":"Wang B, Leja J, Katz H, Inayoshi K, Cleri NJ, De Graaff A, Hviding RE, Van Dokkum P, Greene JE, Labbé I, Matthee JJ, Mcconachie I, Naidu RP, Nelson EJ. 2026. The missing hard photons of Little Red Dots: Their incident ionizing spectra resemble massive stars. The Astrophysical Journal. 1003(1), 10.","chicago":"Wang, Bingjie, Joel Leja, Harley Katz, Kohei Inayoshi, Nikko J. Cleri, Anna De Graaff, Raphael E. Hviding, et al. “The Missing Hard Photons of Little Red Dots: Their Incident Ionizing Spectra Resemble Massive Stars.” <i>The Astrophysical Journal</i>. IOP Publishing, 2026. <a href=\"https://doi.org/10.3847/1538-4357/ae5bab\">https://doi.org/10.3847/1538-4357/ae5bab</a>.","mla":"Wang, Bingjie, et al. “The Missing Hard Photons of Little Red Dots: Their Incident Ionizing Spectra Resemble Massive Stars.” <i>The Astrophysical Journal</i>, vol. 1003, no. 1, 10, IOP Publishing, 2026, doi:<a href=\"https://doi.org/10.3847/1538-4357/ae5bab\">10.3847/1538-4357/ae5bab</a>.","apa":"Wang, B., Leja, J., Katz, H., Inayoshi, K., Cleri, N. J., De Graaff, A., … Nelson, E. J. (2026). The missing hard photons of Little Red Dots: Their incident ionizing spectra resemble massive stars. <i>The Astrophysical Journal</i>. IOP Publishing. <a href=\"https://doi.org/10.3847/1538-4357/ae5bab\">https://doi.org/10.3847/1538-4357/ae5bab</a>","short":"B. Wang, J. Leja, H. Katz, K. Inayoshi, N.J. Cleri, A. De Graaff, R.E. Hviding, P. Van Dokkum, J.E. Greene, I. Labbé, J.J. Matthee, I. Mcconachie, R.P. Naidu, E.J. Nelson, The Astrophysical Journal 1003 (2026).","ama":"Wang B, Leja J, Katz H, et al. The missing hard photons of Little Red Dots: Their incident ionizing spectra resemble massive stars. <i>The Astrophysical Journal</i>. 2026;1003(1). doi:<a href=\"https://doi.org/10.3847/1538-4357/ae5bab\">10.3847/1538-4357/ae5bab</a>"},"OA_type":"gold","year":"2026","department":[{"_id":"JoMa"}],"status":"public","language":[{"iso":"eng"}],"_id":"21882","PlanS_conform":"1","day":"01","issue":"1","title":"The missing hard photons of Little Red Dots: Their incident ionizing spectra resemble massive stars","arxiv":1,"date_updated":"2026-05-18T08:18:39Z","date_published":"2026-05-01T00:00:00Z","ddc":["520"],"user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","OA_place":"publisher","file_date_updated":"2026-05-18T08:17:26Z","publication_identifier":{"issn":["0004-637X"],"eissn":["1538-4357"]},"intvolume":"      1003","publication":"The Astrophysical Journal","abstract":[{"lang":"eng","text":"The nature of little red dots (LRDs) has largely been investigated through their continuum emission, with lines assumed to arise from a broad-line region. In this paper, we instead use recombination lines to infer the intrinsic properties of the central engine. Our analysis first reveals a tension between the ionizing properties implied from Hα and He ii λ4686. The high Hα EWs require copious H-ionizing photons, more than the bluest active galactic nucleus (AGN) ionizing spectra can provide. In contrast, He ii emission is marginally detected, and its low EW is, at most, consistent with the softest AGN spectra. The low He ii/Hβ (∼10−2, <20×  local AGN median) further points to an unusually soft ionizing spectrum. We extend our analysis to dense gas envelopes (quasi-star/black-hole star) and find that hydrogen recombination lines become optically thick and lose diagnostic power, but He ii remains optically thin and a robust tracer. Photoionization modeling with Cloudy rules out standard AGN accretion disk spectra. Alternative explanations include exotic AGN with red rest-optical emission, high average optical depth (>10) from gas/dust, and soft ionizing spectra with abundant H-ionizing photons, consistent with, e.g., a cold accretion disk or a composite of AGN and stars. The latter is an intriguing scenario since high hydrogen densities are highly conducive for star formation, and nuclear star clusters are found in the vicinity of local massive black holes. While previous studies have mostly focused on features dominated by the absorbing hydrogen cloud, the He ii-based diagnostic proposed here represents a crucial step toward understanding the central engine of LRDs."}],"article_type":"original","quality_controlled":"1","article_processing_charge":"Yes","doi":"10.3847/1538-4357/ae5bab","acknowledgement":"B.W. thanks Michael Eracleous for valuable discussions. B.W. and J.L. acknowledge support from JWST-GO-04233.009. B.W. also acknowledges support provided by NASA through Hubble Fellowship grant HST-HF2-51592.001 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under the contract NAS 5-26555. K.I. acknowledges support from the National Natural Science Foundation of China (12573015, W2532003), the Beijing Natural Science Foundation (IS25003), and the China Manned Space Program (CMS-CSST-2025-A09). R.E.H. acknowledges support by the German Aerospace Center (DLR) and the Federal Ministry for Economic Affairs and Energy (BMWi) through program 50OR2403 “RUBIES.”\r\n\r\nThis work is based on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These observations are associated with program # 1433, 2561, 4106, 4233, 5224, 6585. The specific observations analyzed can be accessed via DOI: 10.17909/9hpc-nc45. Computations for this research were performed on the Pennsylvania State University’s Institute for Computational and Data Sciences’ Roar supercomputer; and on computational resources managed and supported by Princeton Research Computing, a consortium of groups including the Princeton Institute for Computational Science and Engineering (PICSciE) and Research Computing at Princeton University. Some of the stellar spectra are retrieved from the POLLUX database (pollux.oreme.org) operated at LUPM (Université de Montpellier—CNRS, France) with the support of the PNPS and INSU. This publication made use of the NASA Astrophysical Data System for bibliographic information.","file":[{"content_type":"application/pdf","access_level":"open_access","date_updated":"2026-05-18T08:17:26Z","date_created":"2026-05-18T08:17:26Z","relation":"main_file","creator":"dernst","file_size":2584417,"file_name":"2026_AstrophysicalJourn_Wang.pdf","checksum":"ee9ebc8ae2304fec04f24b82ebaac8bc","file_id":"21891","success":1}],"publication_status":"published","oa_version":"Published Version","article_number":"10","volume":1003,"fulldoi":"https://doi.org/10.3847/1538-4357/ae5bab","type":"journal_article","DOAJ_listed":"1","tmp":{"name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","image":"/images/cc_by.png","short":"CC BY (4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode"},"publisher":"IOP Publishing","scopus_import":"1"},{"acknowledgement":"We thank the anonymous referee for useful and constructive\r\nfeedback that improved the manuscript. GRB is grateful to Vasily\r\nBelokurov and Sarah Kane for providing the relevant abundances\r\nforthe Aurora data in Fig. 11, as well asto Tiger Yu-Yang Hsiao for\r\nhelpful discussions regarding the MACS 0647-JD source. We are\r\nalso grateful to Gabe Brammerfor useful discussions and his continuous efforts in maintaining and improving the msaexp code,\r\nfrom which the high-z community continues to benefit greatly.\r\nLastly, we also thank the numerous teams of the observational\r\nprograms used in this study, for developing these valuable data\r\nsets. The data used in this study are derived from the following\r\nprograms: 1181 (PI Eisenstein; D. J. Eisenstein et al. 2023a), 1210\r\n(PI Luetzgendorf; D. J. Eisenstein et al. 2023a), 1211 (PI Isaak;\r\nM. V. Maseda et al. 2024), 1286 (PI Luetzgendorf; D. J. Eisenstein\r\net al. 2023a), 1287 (PI Isaak; D. J. Eisenstein et al. 2023a), 1345\r\n(PI Finkelstein; S. L. Finkelstein et al. 2025), 1433 (PI Coe; T. Y.-\r\nY. Hsiao et al. 2024a), 2561 (PI Labbé; R. Bezanson et al. 2022),\r\n2750 (PI Arrabal Haro; P. Arrabal Haro et al. 2023b), 3073 (PI\r\nCastellano; M. Castellano et al. 2024), 3215 (PIs Eisenstein &\r\nMaiolino; D. J. Eisenstein et al. 2023b), 5224 (PIs Oesch & Naidu;\r\nOesch et al. in preparation), 6368 (PI Dickinson; V. Kokorev et al.\r\n2025). The authors acknowledge the aforementioned teams and\r\nPIs where development of their observing program(s) was done\r\nwith a zero-exclusive-access period.\r\nThis work is based on observations made with the\r\nNASA/ESA/CSA JWST. The data were obtained from the\r\nMikulski Archive for Space Telescopes at the Space Telescope\r\nScience Institute, which is operated by the Association of\r\nUniversities for Research in Astronomy, Inc., under NASA\r\ncontract NAS 5-03127 for JWST. The specific observations\r\nanalysed can be accessed via DOI 10.17909/jqj3-ws37. Some\r\nof the data products presented herein were retrieved from the\r\nDawn JWST Archive (DJA). DJA is an initiative of the Cosmic\r\nDawn Center (DAWN), which is funded by the Danish National\r\nResearch Foundation under grant DNRF140.\r\nRSE acknowledges generous financial support from the Peter\r\nand Patricia Gruber Foundation. YF acknowledgessupportsfrom\r\nJSPS KAKENHI Grant Numbers JP22K21349 and JP23K13149.\r\nThis work has received funding from the Swiss State Secretariat\r\nfor Education, Research and Innovation (SERI) under contract\r\nnumber MB22.00072, as well as from the Swiss National Science\r\nFoundation (SNSF) through project grant 200020_207349.","doi":"10.1093/mnras/stag701","file":[{"date_updated":"2026-05-21T06:14:23Z","date_created":"2026-05-21T06:14:23Z","content_type":"application/pdf","access_level":"open_access","checksum":"b8f52c6fc5e06b3a505310e7d5898ecf","creator":"dernst","file_name":"2026_MNRAS_RobertsBorsani.pdf","file_size":3539140,"file_id":"21902","success":1,"relation":"main_file"}],"article_type":"original","abstract":[{"lang":"eng","text":"We investigate the nature and spectroscopic diversity of early galaxies from a sample of 41 sources at $z\\geqslant 10$ with James Webb Space Telescope (JWST)/NIRSpec prism observations. We compare the properties of strong ultraviolet (UV) line emitters, traced by intense C iv emission, with those of more ‘typical’ sources with weak or undetected C iv. The more typical (or ‘C iv-weak’) sources reveal significant scatter in their C iii] line strengths, UV continuum slopes, and physical sizes, spanning C iii] equivalent widths (EWs) of $\\sim$1–51 Å, UV slopes of $\\beta \\sim -1.6$ to $-2.6$, and half-light radii of $\\sim$50–1000 pc. In contrast, C iv-strong sources occupy the tail of these distributions, with C iii] EWs of 16–51 Å, UV slopes $\\beta \\lesssim -2.5$, compact morphologies ($r_{\\rm 50} \\lesssim 100$ pc), and elevated star formation surface densities ($\\Sigma _{\\rm SFR} \\gtrsim 100\\, M_\\odot \\, \\mathrm{yr}^{-1}\\, \\mathrm{kpc}^{-2}$). These properties suggest concentrated starbursts that temporarily outshine the host galaxy. Comparing average properties from composite spectra, we find the diversity of the sample is primarily driven by bursty star formation on very short time-scales ($\\le$3 Myr), with strong C iv emitters observed at the apex of the bursts and sources devoid of emission lines during relative inactivity. An apparent association between strong C iv and enhanced nitrogen abundance suggests both may be modulated by the same duty cycle, reflecting a generic mode of star formation. We show that active galactic nuclei are unlikely to contribute significantly to this duty cycle based on UV line diagnostics and photoionization models. Our results support a picture whereby brief bursts and lulls can explain the spectral diversity and early growth of bright galaxies in the first 500 Myr."}],"publication":"Monthly Notices of the Royal Astronomical Society","article_processing_charge":"Yes","quality_controlled":"1","DOAJ_listed":"1","type":"journal_article","fulldoi":"https://doi.org/10.1093/mnras/stag701","scopus_import":"1","publisher":"Oxford University Press","tmp":{"name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","image":"/images/cc_by.png","short":"CC BY (4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode"},"oa_version":"Published Version","publication_status":"published","volume":548,"article_number":"stag701","department":[{"_id":"JoMa"}],"OA_type":"gold","year":"2026","date_created":"2026-05-20T14:34:29Z","citation":{"ieee":"G. Roberts-Borsani <i>et al.</i>, “JWST spectroscopic insights into the diversity of galaxies in the first 500 Myr: Short-lived snapshots along a common evolutionary pathway,” <i>Monthly Notices of the Royal Astronomical Society</i>, vol. 548, no. 3. Oxford University Press, 2026.","ista":"Roberts-Borsani G, Oesch PA, Ellis R, Weibel A, Giovinazzo E, Bouwens R, Dayal P, Fontana A, Heintz KE, Matthee JJ, Meyer RA, Pentericci L, Shapley A, Tacchella S, Treu T, Walter F, Atek H, Bose S, Castellano M, Fudamoto Y, Morishita T, Naidu RP, Sanders RL, van der Wel A. 2026. JWST spectroscopic insights into the diversity of galaxies in the first 500 Myr: Short-lived snapshots along a common evolutionary pathway. Monthly Notices of the Royal Astronomical Society. 548(3), stag701.","chicago":"Roberts-Borsani, Guido, Pascal A Oesch, Richard Ellis, Andrea Weibel, Emma Giovinazzo, Rychard Bouwens, Pratika Dayal, et al. “JWST Spectroscopic Insights into the Diversity of Galaxies in the First 500 Myr: Short-Lived Snapshots along a Common Evolutionary Pathway.” <i>Monthly Notices of the Royal Astronomical Society</i>. Oxford University Press, 2026. <a href=\"https://doi.org/10.1093/mnras/stag701\">https://doi.org/10.1093/mnras/stag701</a>.","short":"G. Roberts-Borsani, P.A. Oesch, R. Ellis, A. Weibel, E. Giovinazzo, R. Bouwens, P. Dayal, A. Fontana, K.E. Heintz, J.J. Matthee, R.A. Meyer, L. Pentericci, A. Shapley, S. Tacchella, T. Treu, F. Walter, H. Atek, S. Bose, M. Castellano, Y. Fudamoto, T. Morishita, R.P. Naidu, R.L. Sanders, A. van der Wel, Monthly Notices of the Royal Astronomical Society 548 (2026).","apa":"Roberts-Borsani, G., Oesch, P. A., Ellis, R., Weibel, A., Giovinazzo, E., Bouwens, R., … van der Wel, A. (2026). JWST spectroscopic insights into the diversity of galaxies in the first 500 Myr: Short-lived snapshots along a common evolutionary pathway. <i>Monthly Notices of the Royal Astronomical Society</i>. Oxford University Press. <a href=\"https://doi.org/10.1093/mnras/stag701\">https://doi.org/10.1093/mnras/stag701</a>","ama":"Roberts-Borsani G, Oesch PA, Ellis R, et al. JWST spectroscopic insights into the diversity of galaxies in the first 500 Myr: Short-lived snapshots along a common evolutionary pathway. <i>Monthly Notices of the Royal Astronomical Society</i>. 2026;548(3). doi:<a href=\"https://doi.org/10.1093/mnras/stag701\">10.1093/mnras/stag701</a>","mla":"Roberts-Borsani, Guido, et al. “JWST Spectroscopic Insights into the Diversity of Galaxies in the First 500 Myr: Short-Lived Snapshots along a Common Evolutionary Pathway.” <i>Monthly Notices of the Royal Astronomical Society</i>, vol. 548, no. 3, stag701, Oxford University Press, 2026, doi:<a href=\"https://doi.org/10.1093/mnras/stag701\">10.1093/mnras/stag701</a>."},"status":"public","author":[{"full_name":"Roberts-Borsani, Guido","first_name":"Guido","last_name":"Roberts-Borsani"},{"first_name":"Pascal A","last_name":"Oesch","full_name":"Oesch, Pascal A"},{"full_name":"Ellis, Richard","last_name":"Ellis","first_name":"Richard"},{"full_name":"Weibel, Andrea","first_name":"Andrea","last_name":"Weibel"},{"full_name":"Giovinazzo, Emma","last_name":"Giovinazzo","first_name":"Emma"},{"first_name":"Rychard","last_name":"Bouwens","full_name":"Bouwens, Rychard"},{"first_name":"Pratika","last_name":"Dayal","full_name":"Dayal, Pratika"},{"full_name":"Fontana, Adriano","last_name":"Fontana","first_name":"Adriano"},{"full_name":"Heintz, Kasper E","first_name":"Kasper E","last_name":"Heintz"},{"orcid":"0000-0003-2871-127X","full_name":"Matthee, Jorryt J","last_name":"Matthee","id":"7439a258-f3c0-11ec-9501-9df22fe06720","first_name":"Jorryt J"},{"first_name":"Romain A","last_name":"Meyer","full_name":"Meyer, Romain A"},{"full_name":"Pentericci, Laura","first_name":"Laura","last_name":"Pentericci"},{"first_name":"Alice","last_name":"Shapley","full_name":"Shapley, Alice"},{"last_name":"Tacchella","first_name":"Sandro","full_name":"Tacchella, Sandro"},{"first_name":"Tommaso","last_name":"Treu","full_name":"Treu, Tommaso"},{"full_name":"Walter, Fabian","first_name":"Fabian","last_name":"Walter"},{"last_name":"Atek","first_name":"Hakim","full_name":"Atek, Hakim"},{"first_name":"Sownak","last_name":"Bose","full_name":"Bose, Sownak"},{"full_name":"Castellano, Marco","first_name":"Marco","last_name":"Castellano"},{"full_name":"Fudamoto, Yoshinobu","first_name":"Yoshinobu","last_name":"Fudamoto"},{"first_name":"Takahiro","last_name":"Morishita","full_name":"Morishita, Takahiro"},{"full_name":"Naidu, Rohan P","last_name":"Naidu","first_name":"Rohan P"},{"full_name":"Sanders, Ryan L","last_name":"Sanders","first_name":"Ryan L"},{"full_name":"van der Wel, Arjen","last_name":"van der Wel","first_name":"Arjen"}],"oa":1,"has_accepted_license":"1","month":"05","external_id":{"arxiv":["2508.21708"]},"user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","ddc":["520"],"date_updated":"2026-05-21T06:16:04Z","date_published":"2026-05-01T00:00:00Z","publication_identifier":{"eissn":["1365-2966"],"issn":["0035-8711"]},"intvolume":"       548","file_date_updated":"2026-05-21T06:14:23Z","OA_place":"publisher","issue":"3","PlanS_conform":"1","day":"01","language":[{"iso":"eng"}],"_id":"21898","arxiv":1,"title":"JWST spectroscopic insights into the diversity of galaxies in the first 500 Myr: Short-lived snapshots along a common evolutionary pathway"},{"external_id":{"arxiv":["2511.13591"]},"month":"05","has_accepted_license":"1","oa":1,"author":[{"first_name":"Danielle A.","last_name":"Berg","full_name":"Berg, Danielle A."},{"first_name":"Rohan P.","last_name":"Naidu","full_name":"Naidu, Rohan P."},{"full_name":"Chisholm, John","last_name":"Chisholm","first_name":"John"},{"last_name":"Atek","first_name":"Hakim","full_name":"Atek, Hakim"},{"last_name":"Fujimoto","first_name":"Seiji","full_name":"Fujimoto, Seiji"},{"first_name":"Vasily","last_name":"Kokorev","full_name":"Kokorev, Vasily"},{"full_name":"Furtak, Lukas J.","first_name":"Lukas J.","last_name":"Furtak"},{"first_name":"Chiaki","last_name":"Kobayashi","full_name":"Kobayashi, Chiaki"},{"last_name":"Schaerer","first_name":"Daniel","full_name":"Schaerer, Daniel"},{"full_name":"Adamo, Angela","last_name":"Adamo","first_name":"Angela"},{"full_name":"Fei, Qinyue","first_name":"Qinyue","last_name":"Fei"},{"last_name":"Korber","first_name":"Damien","full_name":"Korber, Damien"},{"id":"7439a258-f3c0-11ec-9501-9df22fe06720","last_name":"Matthee","first_name":"Jorryt J","orcid":"0000-0003-2871-127X","full_name":"Matthee, Jorryt J"},{"full_name":"Marques-Chaves, Rui","last_name":"Marques-Chaves","first_name":"Rui"},{"first_name":"Zorayda","last_name":"Martinez","full_name":"Martinez, Zorayda"},{"first_name":"Kristen B.W.","last_name":"Mcquinn","full_name":"Mcquinn, Kristen B.W."},{"last_name":"Muñoz","first_name":"Julian B.","full_name":"Muñoz, Julian B."},{"last_name":"Oesch","first_name":"Pascal A.","full_name":"Oesch, Pascal A."},{"first_name":"Alberto","last_name":"Saldana-Lopez","full_name":"Saldana-Lopez, Alberto"},{"first_name":"Daniel P.","last_name":"Stark","full_name":"Stark, Daniel P."},{"full_name":"Stephenson, Mabel G.","first_name":"Mabel G.","last_name":"Stephenson"},{"full_name":"Hsiao, Tiger Yu Yang","first_name":"Tiger Yu Yang","last_name":"Hsiao"}],"status":"public","citation":{"ista":"Berg DA, Naidu RP, Chisholm J, Atek H, Fujimoto S, Kokorev V, Furtak LJ, Kobayashi C, Schaerer D, Adamo A, Fei Q, Korber D, Matthee JJ, Marques-Chaves R, Martinez Z, Mcquinn KBW, Muñoz JB, Oesch PA, Saldana-Lopez A, Stark DP, Stephenson MG, Hsiao TYY. 2026. A fleeting GLIMPSE of N/O enrichment at cosmic dawn: Evidence for Wolf Rayet N stars in a z = 6.1 galaxy. The Astrophysical Journal. 1003(2), 112.","chicago":"Berg, Danielle A., Rohan P. Naidu, John Chisholm, Hakim Atek, Seiji Fujimoto, Vasily Kokorev, Lukas J. Furtak, et al. “A Fleeting GLIMPSE of N/O Enrichment at Cosmic Dawn: Evidence for Wolf Rayet N Stars in a z = 6.1 Galaxy.” <i>The Astrophysical Journal</i>. IOP Publishing, 2026. <a href=\"https://doi.org/10.3847/1538-4357/ae5e4c\">https://doi.org/10.3847/1538-4357/ae5e4c</a>.","ieee":"D. A. Berg <i>et al.</i>, “A fleeting GLIMPSE of N/O enrichment at cosmic dawn: Evidence for Wolf Rayet N stars in a z = 6.1 galaxy,” <i>The Astrophysical Journal</i>, vol. 1003, no. 2. IOP Publishing, 2026.","ama":"Berg DA, Naidu RP, Chisholm J, et al. A fleeting GLIMPSE of N/O enrichment at cosmic dawn: Evidence for Wolf Rayet N stars in a z = 6.1 galaxy. <i>The Astrophysical Journal</i>. 2026;1003(2). doi:<a href=\"https://doi.org/10.3847/1538-4357/ae5e4c\">10.3847/1538-4357/ae5e4c</a>","apa":"Berg, D. A., Naidu, R. P., Chisholm, J., Atek, H., Fujimoto, S., Kokorev, V., … Hsiao, T. Y. Y. (2026). A fleeting GLIMPSE of N/O enrichment at cosmic dawn: Evidence for Wolf Rayet N stars in a z = 6.1 galaxy. <i>The Astrophysical Journal</i>. IOP Publishing. <a href=\"https://doi.org/10.3847/1538-4357/ae5e4c\">https://doi.org/10.3847/1538-4357/ae5e4c</a>","short":"D.A. Berg, R.P. Naidu, J. Chisholm, H. Atek, S. Fujimoto, V. Kokorev, L.J. Furtak, C. Kobayashi, D. Schaerer, A. Adamo, Q. Fei, D. Korber, J.J. Matthee, R. Marques-Chaves, Z. Martinez, K.B.W. Mcquinn, J.B. Muñoz, P.A. Oesch, A. Saldana-Lopez, D.P. Stark, M.G. Stephenson, T.Y.Y. Hsiao, The Astrophysical Journal 1003 (2026).","mla":"Berg, Danielle A., et al. “A Fleeting GLIMPSE of N/O Enrichment at Cosmic Dawn: Evidence for Wolf Rayet N Stars in a z = 6.1 Galaxy.” <i>The Astrophysical Journal</i>, vol. 1003, no. 2, 112, IOP Publishing, 2026, doi:<a href=\"https://doi.org/10.3847/1538-4357/ae5e4c\">10.3847/1538-4357/ae5e4c</a>."},"date_created":"2026-05-31T22:02:12Z","year":"2026","OA_type":"gold","department":[{"_id":"JoMa"}],"title":"A fleeting GLIMPSE of N/O enrichment at cosmic dawn: Evidence for Wolf Rayet N stars in a z = 6.1 galaxy","arxiv":1,"_id":"21930","language":[{"iso":"eng"}],"PlanS_conform":"1","day":"20","issue":"2","OA_place":"publisher","file_date_updated":"2026-06-02T08:46:08Z","publication_identifier":{"issn":["0004-637X"],"eissn":["1538-4357"]},"intvolume":"      1003","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","date_published":"2026-05-20T00:00:00Z","date_updated":"2026-06-02T08:46:20Z","ddc":["520"],"quality_controlled":"1","article_processing_charge":"Yes","publication":"The Astrophysical Journal","abstract":[{"lang":"eng","text":"We present the discovery of extreme nitrogen enrichment by Wolf Rayet nitrogen (WN) stars in the metal-poor (∼10%Z⊙), lensed, compact (Reff ∼ 20 pc) galaxy RXCJ2248 at z = 6.1, revealed by unprecedentedly deep\r\nJWST/NIRSpec medium-resolution spectroscopy from the GLIMPSE-D Survey. The exquisite signal-to-noise\r\nratio reveals multiple high-ionization nebular lines and broad Balmer and [O III] components (FWHM\r\n∼700–3000 km s\r\n−1\r\n). We detect broadened He II λ1640 and λ4687 (FWHM ∼ 530 km s\r\n−1\r\n) and strong N III λ4642\r\nemission consistent with a population of WN stars, making RXCJ2248 the most distant galaxy with confirmed\r\nWolf Rayet (WR) features to date. We measure the multiphase nebular density across five ions, the direct-method\r\nmetallicity (\r\n12 + log(O/H) = 7.753 ± 0.025\r\n), and a nonuniform elemental enrichment pattern of extreme N/O\r\nenhancement (\r\nlog(N/O) = 0.391 ± 0.037\r\nfrom N+, N+2\r\n, and N+3\r\n) but suppressed C/O relative to empirical\r\nC/N trends. We show that this abundance pattern can be explained by enrichment from a dual-burst with a low\r\nWR carbon/WN ratio, as expected at low metallicities. Crucially, these signatures can only arise during a brief,\r\nrare evolutionary window shortly after a burst (∼3–6 Myr), when WN stars dominate chemical feedback but\r\nbefore dilution by later yields (e.g., supernovae). The observed frequency of strong N emitters at high−z implies a\r\n∼50 Myr burst duty cycle, suggesting that N/O outliers may represent a brief but ubiquitous phase in the\r\nevolution of highly star-forming early galaxies. The WN detection in RXCJ2248, therefore, provides the first\r\ndirect evidence of WR-driven nitrogen enrichment in the first billion years of the Universe and a novel timing\r\nargument for the bursty star formation cycles that shaped galaxies at cosmic dawn."}],"article_type":"original","file":[{"file_id":"21938","success":1,"creator":"dernst","file_size":21249354,"file_name":"2026_AstrophysicalJour_Berg.pdf","checksum":"1058555fdede45e10fca25d74e7977bc","relation":"main_file","date_updated":"2026-06-02T08:46:08Z","date_created":"2026-06-02T08:46:08Z","access_level":"open_access","content_type":"application/pdf"}],"doi":"10.3847/1538-4357/ae5e4c","acknowledgement":"\r\nThe American Astronomical Society, find out more.\r\n\r\nThe following article isOpen access\r\nA Fleeting GLIMPSE of N/O Enrichment at Cosmic Dawn: Evidence for Wolf Rayet N Stars in a z = 6.1 Galaxy\r\nDanielle A. Berg, Rohan P. Naidu, John Chisholm, Hakim Atek, Seiji Fujimoto, Vasily Kokorev, Lukas J. Furtak, Chiaki Kobayashi, Daniel Schaerer, Angela Adamo, Qinyue Fei, Damien Korber, Jorryt Matthee, Rui Marques-Chaves, Zorayda Martinez, Kristen. B. W. McQuinn, Julian B. Muñoz, Pascal A. Oesch, Alberto Saldana-Lopez, Daniel P. Stark, Mabel G. Stephenson, and Tiger Yu-Yang HsiaoHide full author list\r\n\r\nPublished 2026 May 20 • © 2026. The Author(s). Published by the American Astronomical Society.\r\nThe Astrophysical Journal, Volume 1003, Number 2\r\nCitation Danielle A. Berg et al 2026 ApJ 1003 112\r\nDOI 10.3847/1538-4357/ae5e4c\r\n\r\nDownloadArticle PDFDownloadArticle ePub\r\nAuthors\r\nFigures\r\nTables\r\nReferences\r\nArticle data\r\nDownload PDFDownload ePub\r\nArticle metrics\r\n173 Total downloads\r\n\r\nShare this article\r\nArticle information\r\nAbstract\r\nWe present the discovery of extreme nitrogen enrichment by Wolf Rayet nitrogen (WN) stars in the metal-poor (∼10%Z⊙), lensed, compact (Reff ∼ 20 pc) galaxy RXCJ2248 at z = 6.1, revealed by unprecedentedly deep JWST/NIRSpec medium-resolution spectroscopy from the GLIMPSE-D Survey. The exquisite signal-to-noise ratio reveals multiple high-ionization nebular lines and broad Balmer and [O iii] components (FWHM ∼700–3000 km s−1). We detect broadened He ii λ1640 and λ4687 (FWHM ∼ 530 km s−1) and strong N iii λ4642 emission consistent with a population of WN stars, making RXCJ2248 the most distant galaxy with confirmed Wolf Rayet (WR) features to date. We measure the multiphase nebular density across five ions, the direct-method metallicity (\r\n), and a nonuniform elemental enrichment pattern of extreme N/O enhancement (\r\n from N+, N+2, and N+3) but suppressed C/O relative to empirical C/N trends. We show that this abundance pattern can be explained by enrichment from a dual-burst with a low WR carbon/WN ratio, as expected at low metallicities. Crucially, these signatures can only arise during a brief, rare evolutionary window shortly after a burst (∼3–6 Myr), when WN stars dominate chemical feedback but before dilution by later yields (e.g., supernovae). The observed frequency of strong N emitters at high−z implies a ∼50 Myr burst duty cycle, suggesting that N/O outliers may represent a brief but ubiquitous phase in the evolution of highly star-forming early galaxies. The WN detection in RXCJ2248, therefore, provides the first direct evidence of WR-driven nitrogen enrichment in the first billion years of the Universe and a novel timing argument for the bursty star formation cycles that shaped galaxies at cosmic dawn.\r\n\r\nExport citation and abstract\r\nBibTeXRIS\r\n\r\nPrevious article in issue\r\nNext article in issue\r\n\r\nOriginal content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.\r\n\r\n1. Introduction\r\nA key tracer of galaxy evolution is the change in their chemical composition over time. The metallicity of a galaxy is a sensitive observational diagnostic of its past star formation history and present-day evolutionary state given that metallicity increases with each successive generation of massive star yields (e.g., M. Tosi 1988; J.-R. Roy & D. Kunth 1995; D. A. Berg et al. 2019; R. Maiolino & F. Mannucci 2019). Oxygen is an important tracer of metallicity because it is the most abundant element in the Universe after H and He and is convenient to observe, with ubiquitous emission lines from H ii regions in the rest-frame optical regime. While O emission in dwarf and spiral galaxies has been widely observed in the rest-frame optical and UV (e.g., R. C. Kennicutt 1992; Y. I. Izotov & T. X. Thuan 1999; L. van Zee & M. Haynes2006; D. A. Berg et al. 2012, 2016, 2019; P. Senchyna et al. 2017; N. S. J. Rogers et al. 2022), the N emission in these same galaxies has been predominantly traced only in the optical through the low-ionization [N ii] λλ6550,6585 emission lines. In general, there is a surprising dearth of detections of the high-ionization N emission counterparts in local galaxies, totaling less than 10 galaxies with significant detections of either N iv] λλ1483,1486 or N iii] λ1750 (e.g., M. Mingozzi et al. 2022; Z. Martinez et al. 2025). However, with the advent of JWST, there is a growing prevalence of z ≳ 5 galaxies with extreme properties, including intense UV N emission (e.g., A. J. Bunker et al. 2023; Y. Isobe et al. 2023; M. Castellano et al. 2024; T. Y.-Y. Hsiao et al. 2024; X. Ji et al. 2024; R. Marques-Chaves et al. 2024; D. Schaerer et al. 2024; M. Curti et al. 2025a; Y. Harikane et al. 2025a; R. P. Naidu et al. 2026; M. W. Topping et al. 2025b).\r\n\r\nThe first noted, and one of the most distant, examples of extreme rest-frame UV N emission comes from the spectroscopically confirmed z = 10.6 galaxy, GN-z11. JWST spectra of GN-z11 revealed surprisingly strong N iv] λλ1483,1486 and N iii] λ1750 emission (e.g., A. J. Bunker et al. 2023) that corresponds to supersolar nitrogen-to-oxygen (N/O) enrichment (\r\n; e.g., A. J. Cameron et al. 2023). Subsequently, enhanced N/O has been reported in a number of high−z galaxies, including GDS 3073 (z = 5.55; X. Ji et al. 2024), RXCJ2248-ID (z = 6.10; M. W. Topping et al. 2024), A1703-zd6 (z = 7.04; M. W. Topping et al. 2025b), CEERS-1019 (z = 8.68; R. Marques-Chaves et al. 2024), GNz9p4 (z = 9.38; D. Schaerer et al. 2024), GHZ9 (z = 10.15; L. Napolitano et al. 2025), GHZ2 (z = 12.34; M. Castellano et al. 2024), and MoM-z14 (z = 14.44; R. P. Naidu et al. 2026). For a review of nitrogen line detections, see D. P. Stark et al. (2025). Such strong nebular N+3 emission requires a relatively hard ionizing radiation field (≳47.4 eV), where models of massive stars predict few photons. On the other hand, N+2 has a lower ionization potential (∼29.6 eV), but statistically significant detections are strikingly rare in integrated galaxy spectra (e.g., D. A. Berg et al. 2018; M. Mingozzi et al. 2022; A. J. Bunker et al. 2023; P. Senchyna et al. 2024) and are only expected to be strong at the highest possible nebular temperatures (∼2.5 × 104 K). Furthermore, the timing of the incredibly high N/O abundances reported for the high-redshift UV N emitters just a few 100 Myr after the Big Bang is unexpected.\r\n\r\nThe discovery of significant, rapid nitrogen enhancement so early in the Universe was surprising because it contradicts our longstanding understanding of N production. In typical chemical evolution modeling, some nitrogen enrichment can occur early on via core collapse supernova (CCSN), but substantial nitrogen enrichment only occurs 100 s of megayears after the onset of star formation via asymptotic giant branch (AGB) stars (e.g., F. Vincenzo et al. 2019; C. Kobayashi et al. 2020). Thus, alternative, faster enrichment methods are needed to explain substantial nitrogen enrichment in early galaxies. As a result, the necessary ionizing flux and conditions to produce the unexpectedly strong N+3 and N+2 emission observed in galaxies beyond z ∼ 5 have been attributed to more extreme sources, such as active galactic nuclei (AGN; R. Maiolino et al. 2024), Wolf Rayet (WR) stars (e.g., P. Senchyna et al. 2024; K. Watanabe et al. 2024; M. L. P. Gunawardhana et al. 2025), globular cluster precursors (e.g., C. Charbonnel et al. 2023; X. Ji et al. 2026), super star clusters (e.g., M. Pascale et al. 2023), very massive stars (VMSs: M⋆ > 102 M⊙; e.g., J. S. Vink 2023; Y. Shi et al. 2026), or supermassive stars (M⋆ > 103 M⊙; e.g., C. Charbonnel et al. 2023; C. Nagele & H. Umeda 2023), tidal disruption events (e.g., A. J. Cameron et al. 2023; K. Watanabe et al. 2024), and more.\r\n\r\nMost of our understanding of WR stars has been built from observations of individual resolved stars in a handful of galaxies in the Local Group, with almost no direct spectroscopic evidence for the prevalence of WR stars in more distant galaxies. To date, only two systems at Cosmic Noon (z ≈ 2–3) have confirmed signatures of WR stars: MARTA-4327 at z = 2.224 (hereafter, M4327; M. Curti et al. 2025b) and the Sunburst Arc at z = 2.37 (T. E. Rivera-Thorsen et al. 2024). Extending such detections to earlier cosmic epochs is crucial for understanding the role of massive stars in shaping the chemical evolution of galaxies in the first Gyr.\r\n\r\nHere, we investigate the z = 6.1 lensed galaxy RXCJ2248-ID3. RXCJ2248-ID was first identified by F. Boone et al. (2013), I. Balestra et al. (2013), and A. Monna et al. (2014) and discovered to be a high-ionization, compact, metal-poor, N-enhanced galaxy by R. Mainali et al. (2017), K. B. Schmidt et al. (2017), and M. W. Topping et al. (2024). We present extremely deep JWST/NIRSpec observations of RXCJ2248-ID3 that provide the highest-redshift spectroscopic evidence of WR nitrogen (WN) stars to date, which provide a physically consistent mechanism driving its extreme nitrogen enrichment (M. W. Topping et al. 2024). The remainder of this paper is organized as follows. The observations and data reduction are briefly described in Section 2.1, followed by a description of the emission-line fits, including the broad lines related to the WR feedback, in Section 2.2. We present the discovery of WN stars at z ∼ 6 via their spectral signatures in Section 3. We determine new nebular properties and O, C, N, and Si abundances in Section 4.3 and compare them to populations of both low- and high-redshift galaxies. We discuss the source of N enrichment in the early Universe and subsequently estimate mass production and timing arguments in Section 5. Finally, we present our conclusions in Section 6. Throughout this work, we adopt cosmological parameters of H0 = 70 km s−1 Mpc−1, Ωm = 0.30, and ΩΛ = 0.7 and the solar abundance pattern from M. Asplund et al. (2021).\r\n\r\n2. JWST/NIRSpec Spectra\r\nRXCJ2248 is a galaxy at z ∼ 6.1 that is lensed into multiple images by the Abell S1063 cluster (α = 22:48:44.13, δ =−44:31:57.50) at a redshift of z = 0.348. We present an analysis of the brightest image, RXCJ2248-ID3 (J = 25.0), which has a magnification of μ ∼ 7 (L. Furtak et al. 2025). RXCJ2248-ID was discovered as a z ∼ 6 candidate (F. Boone et al. 2013; A. Monna et al. 2014) using the 16-band HST photometry of the CLASH Survey and spectroscopically confirmed via VIsible Multi-Object Spectrograph (VIMOS)/VLT observations by I. Balestra et al. (2013). RXCJ2248-ID3 was soon found to be an exciting extreme emission-line galaxy via ground-based spectroscopy (R. Mainali et al. 2017), with strong detections of high-ionization emission such as O iii] λλ1661,1666 and C ivλλ1548,1550 but no He ii, suggesting star formation as the ionizing source rather than an AGN.\r\n\r\nThe early spectra of RXCJ2248-ID3 motivated further rest-UV+optical study with JWST/NIRSpec by M. W. Topping et al. (2024). This work performed direct metallicity calculations to show that RXCJ2248-ID3 is one of the most extreme N/O-enhanced (), metal-poor () galaxies, with high-ionization ([O iii] λ5008/[O ii] λ3728 = 184) and high nebular density (6.4 × 104 ≤ ne(cm−3) ≤3.1 × 105). They also used spectral energy distribution (SED) fitting with a constant star formation history to characterize its low stellar mass (M⋆ ∼ 108 M⊙) and the young-massive star population (∼2 Myr) of RXCJ2248. M. W. Topping et al. (2024), therefore, suggest that the N/O enrichment may be due to a short-lived phase that many z > 6 bursty galaxies experience. In this paper, we build on the work of M. W. Topping et al. (2024) with new, extraordinarily deep rest-optical JWST/NIRSpec observations of RXCJ2248-ID3 from the GLIMPSE-D Survey, a Director’s Discretionary Time (DDT) follow-up program described below.\r\n\r\n2.1. Observations and Reduction\r\nThe work presented here uses both the rest-UV JWST/NIRSpec archival spectra from JWST PID 2478 (PI Stark) and new rest-optical JWST/NIRSpec spectra from the GLIMPSE-D Survey, which is an extension of the GLIMPSE Survey. Properties of RXCJ2248-ID and observation details are presented in Table 1.\r\n\r\nTable 1. Properties of RXCJ2248-ID3\r\n\r\nJWST/NIRSpec Observations\r\nGrating/Filter\t(s)\tPI/PID\r\nG140M/F100LP\t6215\tStark/2478\r\nG235M/F170LP\t1576\tStark/2478\r\nG395M/F290LP\t107,228\tFujimoto & Naidu/9223\r\nMeasured Properties\r\nProperty\tValue\tReferences\r\nR.A.\t+22:48:45.81\tThis work\r\nDecl.\t−44:32:14.95\tThis work\r\nz\t6.1025 ± 0.0013\tThis work\r\nμ\t6.8877\tL. Furtak et al. (2025)\r\nReff (pc)\t\tA. Claeyssens (2025)\r\nM⋆ (M⊙)\t\tA. Claeyssens (2025)\r\nΣ⋆ (M⊙ pc−2)\t\tA. Claeyssens (2025)\r\nSFRHα (M⊙ yr−1)\t3.2\tThis work, Section 5.3\r\nSFRSED,1Myr\t4.7\tA. Claeyssens (2025)\r\nSFRSED,10Myr\t4.1\tA. Claeyssens (2025)\r\nΣSFR (M⊙ yr−1 kpc−2)\t1.34 × 103\tThis work\r\ntage (Myr)\t\tA. Claeyssens (2025)\r\n12+log(O/H)\t7.753 ± 0.025\tThis work, Section 4.3.1\r\nlog(N/O)\t−0.391 ± 0.037\tThis work, Section 4.3.2\r\nNote. Top: JWST/NIRSpec observations of RXCJ2248-ID3, including archival observations from PID 2478 (PI: Stark) and very deep GLIMPSE-D observations from PID 9223 (PI: Fujimoto & Naidu). Columns (1)–(3) list the grating/filter, exposure time, and principle investigator/PID. Bottom: Measured global properties of RXCJ2248-ID3. The R.A. and decl. are the extraction coordinates for RXCJ2248-ID3. The redshift was determined from the GLIMPSE-D spectrum emission lines. GLIMPSE imaging was used to determine the lensing model magnification, μ. Effective radius of the RXCJ2248-ID3 clump, stellar mass, and current massive star population age are from the SED modeling of A. Claeyssens (2025), while the SFR was determined from both the SED fitting and the narrow-component, collisions-corrected Hα flux (see Section 5.3), all corrected for the lensing factor. The star formation rate surface density was determined using the SFRHα. The metallicity and relative N/O abundance were determined using the direct method.\r\n\r\nDownload table as: \r\nASCIITypeset image\r\n\r\nThe GLIMPSE Survey is a large Cycle 2 JWST program (PID 3293; PIs Atek & Chisholm) that performed ultradeep NIRCam imaging (∼30.8 mag at 5σ over 0.8–5 μm) in seven broadband and two medium-band filters of the lensing cluster Abell S1063 (H. Atek et al. 2025). A. Claeyssens (2025) performed size and photometric measurements of RXCJ2248-ID in the different multiple images. The SED fitting was performed with the Bayesian Analysis of Galaxies for Physical Inference and Parameter Estimation (BAGPIPES; A. C. Carnall et al. 2018) code with Binary Population and Spectral Synthesis (BPASS v2.14, J. J. Eldridge et al. 2017) stellar population synthesis burst models and cloudy v23.01 photoionization models (M. Chatzikos et al. 2023; C. M. Gunasekera et al. 2023). Priors were used to be physically consistent with the source, i.e., high-ionization parameter (), low extinction (Av < 0.5 mag), low metallicity (Z < 0.4 Z⊙), and bursty star formation (τ = 1 Myr, i.e., close to a single burst, or τ = 10 Myr). The resulting best fit has a young age ( Myr) and low stellar mass of but within a compact size of pc such that the stellar mass surface density is . This value is akin to the highest densities found in globular clusters, similar to the ones reported for young star clusters and clumps at high redshift (A. Claeyssens et al. 2025; M. Messa et al. 2026), and broadly consistent with the conclusions presented in M. W. Topping et al. (2024).\r\n\r\nSubsequent medium-resolution (R ∼ 1000) spectra of RXCJ2248-ID3 were obtained as part of the follow-up GLIMPSE-D Survey: JWST DDT Program 9223 (PIs Fujimoto & Naidu) targeting a Pop III candidate in S. Fujimoto et al. (2025) using NIRSpec Multi-Object Spectroscopy (MOS) with the G395M grating and F290LP filter. As part of this program, RXCJ2248-ID3 was observed for a total of 13 exposures using a 3-point nod pattern and NRSIRS2 readout, totaling ∼30 hr of integration. The MSA slit positions covering RXCJ2248-ID3 of the three pointings are shown in Figure 1.\r\n\r\nZoom InZoom OutReset image size\r\nFigure 1. JWST/NIRSpec MSA slits targeting RXCJ2248-ID3 for each of the three exposures in the GLIMPSE-D program. The two pointings that are closely aligned (solid purple regions) have the same wavelength coverage, while the pointing offset to the lower left (dashed region) has somewhat reduced blue coverage. All three pointings were used in the spectrum coaddition.\r\n\r\nDownload figure:\r\n\r\nStandard imageHigh-resolution image\r\nWe augment the rest-optical GLIMPSE-D data with archival rest-far-UV G140M/F100LP and rest-near-UV G235M/F170LP observations from PID 2478 (PI Stark), covering the rest-frame ∼1400–4000 Å range. This program also observed the G395M/F290LP setting, but we only use the significantly deeper GLIMPSE-D G395M observations here. Multiple images of RXCJ2248 were identified and observed in program #2478. M. W. Topping et al. (2024) utilized these data by coadding the spectra of the individual images. In contrast, only the brightest image (ID3) was observed in the GLIMPSE-D Survey. To ensure consistency, we therefore restricted our analysis to the G140M and G235M spectra of ID3 obtained in program #2478. As a result, our G140M and G235M measurements are not directly comparable to those presented by M. W. Topping et al. (2024).\r\n\r\nThe data were reduced using v0.9.8 of the msaexp pipeline (G. Brammer 2022), following the standard routines described in A. de Graaff et al. (2025), K. E. Heintz et al. (2025), and F. Valentino et al. (2025). Briefly, level-2 calibrated products from MAST are subject to a series of custom corrections that account for, e.g., 1/f noise, bar vignetting, and detector bias. We used the “local” nodded background subtraction. The 2D spectra were drizzled onto a common wavelength grid and 1D spectra were optimally extracted using a profile model that accounts for, e.g., the wavelength-dependent PSF and offsets from the nominal position expected from the catalog. Line centers were measured for the strongest emission lines in the G395M spectrum (i.e., Hδ, Hγ, [O iii] λ4364, Hβ, [O iii] λλ4960,5008, He iλ5877, Hα, He iλ7067) and used to determine a redshift of z = 6.1025 ± 0.0013. Note that the bluest portion of the G395M tends to favor a slightly lower redshift (i.e., z ∼ 6.1000), while the reddest portion favors a slightly higher redshift (i.e., z ∼ 6.1034). The three individual 1D extracted spectra were then normalized to the common continuum flux scale of the first spectrum at rest-wavelengths of ∼6000–62000 Å prior to coadding. Spectral coaddition was performed as a weighted average using the inverse variance as the weight.\r\n\r\nThe resulting spectrum, shown in Figure 2, covers an observed wavelength range ∼2.8–5.5 μm, which corresponds to a rest-optical range of ∼3900–7740 Å. Note that the third pointing (dashed slits in Figure 1) has reduced wavelength coverage such that the blue end begins at ∼4265. The deep GLIMPSE-D spectra provide unparalleled signal-to-noise ratio (S/N; >5 at 5100 Å continuum) that enable rest-optical diagnostics typically reserved for nearby galaxies.\r\n\r\nZoom InZoom OutReset image size\r\nFigure 2. JWST/NIRSpec rest-frame UV and optical spectra of RXCJ2248-ID3 highlighting the first object known with simultaneously detected emission from N+, N+2, and N+3 (see, also, M. W. Topping et al. 2024) and WR features. The second row shows the main emission UV emission-line detections from the archival G140M/F100LP spectrum, with significant detections of several high-ionization emission lines, including N iv] λλ1483,1486, C iv λλ1548,1550, He ii λ1640, O iii] λλ1661,1666, N iii] λ1750, and C iii] λλ1907,1909. The third row shows the blue end of the optical spectrum, where the left-hand panel shows the archival G235M/F170LP spectrum, which includes the low-ionization [O ii] λλ3727,3730 doublet. The right-hand panel of the third row and the fourth row shows the extremely high S/N GLIMPSE-D optical spectrum, enabling detections of several weak features. Note that some of the important features to this work are highlighted in the zoom in panels in the top row. In particular, the last panel reveals the most distant WR detection to date, with the λ4650 WR bump showing emission from N iii λ4642, indicative of nitrogen enrichment from WN stars. Note that not all of the labeled lines correspond to line detections.\r\n\r\nDownload figure:\r\n\r\nStandard imageHigh-resolution image\r\n2.2. Emission-line Measurements\r\nIn order to perform a consistent analysis of our data, we measure emission-line fluxes for both the archival spectra and the new GLIMPSE-D spectra presented here. We fit neighboring emission lines simultaneously using Gaussian profiles with the lmfit package (M. Newville et al. 2015) in Python. Purely nebular lines (i.e., lines without possible stellar contributions or resonant effects) close in wavelengths were constrained to have the same full width at half-maximum (FWHM) velocity widths. Additionally, the relative wavelength spacing between lines was constrained to laboratory values and doublets with constant flux ratios set by atomic physics were constrained to their theoretical values, with small uncertainty allowances. The uncertainties on the line fluxes were estimated as the standard error derived from the least-squares minimization in lmfit, which considers the uncertainty on the Gaussian profile and linear continuum.\r\n\r\nBroad emission components are clearly visible at the base of some of the emission lines in the GLIMPSE-D spectrum of RXCJ2248-ID3. Such broad emission features can be produced by stellar winds, shocks, or turbulence. Since He iiλ1640 and λ4687 emission lines can be affected by stellar winds, we fit these features with an unconstrained Gaussian width. Using the jwst-msa package (A. de Graaff et al. 2024), we deconvolved all measured FWHMs with the modeled wavelength-dependent line spread function (LSF). We found the He ii lines to be broadened compared to purely nebular lines. For the He iiλ 4687 line, the velocity width is 528 ± 100 km s−1, which is more than two times broader than the narrow nebular Hβ component with vFWHM = 243 ± 25 km s−1.\r\n\r\nThe strongest rest-optical H (Hγ, Hβ, and Hα) and [O iii] (λ4364, λλ4960,5008) emission lines have complex profiles with both narrow and broad emission components. Such broad components may also be present in the rest-UV and fainter rest-optical emission lines, but none are obvious given the lower S/N of these emission features and/or underlying continuum. To fit these profiles, we tested three different multicomponent profile combination fits for the Hα + [N ii] complex. For all three fits, the narrow Hα and [N ii] λλ6550,6585 lines were fit by Gaussians with a single velocity width, but the broad component was fit with either: (1) a single Gaussian profile, (2) two Gaussian profiles, or (3) a single exponential profile. The single broad Gaussian profile fit had strong residuals near the center of the broad component, so did not provide a good fit to the observed emission profile. Both the double Gaussian profile and the exponential profile provided relatively good visual fits, but the double Gaussian fit had a lower reduced chi-squared ( vs ) and Bayesian inference criteria (BIC2Gauss = 36 versus (BICexp. = 87), and so was adopted as the better statistical fit.\r\n\r\nThe right panel of Figure 3 shows the best multicomponent fit to the Hα + [N ii] complex. Since all kinematically similar lines in the Balmer emission series arise from the same gas, we expect the Hβ and Hγ profiles to be well fit by scaling the Hα best fit. Therefore, we constrained the velocity widths of the Hβ and Hγ emission components to match the narrow + double broad Gaussian Hα fit, accounting for the wavelength-dependent LSF. We found excellent fit results, with similarly small reduced-χ2 and BIC values. This means that the H i lines are well fit by a profile with (1) a strong, narrow (∼250 km s−1) nebular component, (2) a moderate (∼20% of total flux), broad component (∼670 km s−1), and (3) a weak (∼10% of total flux), very broad (∼2530 km s−1) component.\r\n\r\nZoom InZoom OutReset image size\r\nFigure 3. Multicomponent emission-line fits to the GLIMPSE spectrum of RXCJ2248-ID for Hα λ6565 + [N II] λλ6549,6585 (left panels), Hβ λ4863 + [O III] λλ4960,5008 (middle panels), and Hγ λ4342 + [O III] λ4364 (right panels). When fit with single, narrow Gaussian components (e.g., purple and yellow filled Gaussians), all three line complexes show strong, broad component residual flux. The resulting best fit to each line is comprised of a single narrow Gaussian plus two broad Gaussians, where the relevant component velocity widths are tied together: The Hα λ6565 + [N ii] λλ6549,6585 complex fit provided the velocity width constraints for the H Balmer line narrow (purple Gaussians) and broad components (blue and green Gaussians) and, subsequently, the Hβ λ4863 + [O iii] λλ4960,5008 fit constrained the [O iii] narrow (yellow Gaussian) and broad (orange and red Gaussians) velocity widths that were then used in the Hγ λ4342 + [O iii] λ4364 fit. Note that additional faint lines (e.g., He i λ5017) were included in the fit in the middle panel. Careful accounting for the residual broad flux has a significant impact on the derived nebular reddening, temperature, metallicity, and N/O abundance.\r\n\r\nDownload figure:\r\n\r\nStandard imageHigh-resolution image\r\nThe [O iii] λλ4960,5008 doublet lines are also well fit by a narrow Gaussian plus double Gaussian broad component profile, with the relative fluxes of each component constrained to the theoretical ratio. While the narrow-component FWHM was set to the velocity width of the narrow Balmer lines, convolved with the LSF, we allowed the FWHM of the two broad [O iii] components to vary freely and found widths of ∼890 km s−1 and ∼2980 km s−1, respectively. The similarity between the [O iii] and H i velocity widths of the broad components argues against emission from an AGN directly (where high densities cause collisional de-excitation of [O iii]) and is more consistent with stellar or AGN driven winds (e.g., Y. I. Izotov & T. X. Thuan 2008; G. Gräfener & J. S. Vink2015; G. Gräfener et al. 2017; C. J. Burke et al. 2021). Interestingly, the broad components of the H i lines compose a larger fraction of their total flux (∼20% and 10%, respectively) than [O iii] (∼10% and 5%, respectively).\r\n\r\nThe resulting fit to the Hβ + [O iii] λλ4960,5008 complex is shown in the middle panel of Figure 3 to be an excellent fit, with minimal residuals. The exquisite S/N of the GLIMPSE spectrum also reveals broad wings on the [O iii] λ4364 profile, as seen in the left panel of Figure 3. Therefore, we also applied the narrow Gaussian plus double Gaussian broad component profile to [O iii] λ4364, constraining the velocity widths to the values measured for [O iii] λλ4960,5008.\r\n\r\nDouble broad components with similar velocity widths (750 and 2500 km s−1, respectively) are seen in the z ∼ 0 extreme emission-line galaxies, J1044+0353 and J1418+2102, reported in D. A. Berg et al. (2021). However, each broad component observed in these nearby analogs only accounts for 1%–3% of the total H i flux. This sort of broad component emission from the Balmer H and [O iii] lines with widths (1000–2000 km s−1) and fractional fluxes of 1%–2% is commonly found in spectra of blue compact dwarf galaxies (BCDs; e.g., Y. I. Izotov et al. 2006, 2007). This suggests that bulk motion of the gas is typical in these metal-poor, bursty environments, but for a larger mass of gas in RXCJ2248-ID3.\r\n\r\nThe sensitive accounting of broad component emission afforded by the deep GLIMPSE-D spectra is important because even a small fraction of broad emission around H emission line can significantly affect the fit to weak lines such as [N ii] λλ6550,6585 (e.g., D. A. Berg et al. 2021). In RXCJ2248-ID, the broad components compose a significant fraction of the total H and [O iii] fluxes, and so are critical to properly measure not only the [N ii] λ6585 emission but also the [O iii] λ4364, Hβ, [O iii] λλ4960,5008, and Hα narrow-line fluxes. For this reason, we adopt the narrow-line fluxes from our best multicomponent fits for the remaining analysis; we reserve further investigation of the the broad emission for a forthcoming paper.\r\n\r\nAs noted above, the UV spectra do not have sufficient S/N to decompose narrow and possible broad components. As a result, density diagnostics and relative abundance ratios determined from UV line ratios may include contributions from multiple kinematic components. If the broad components arise from gas with distinct physical conditions, this could introduce systematic offsets. We test the level of bias possible due to broad component contamination of narrow-line fluxes by adopting the relative narrow and broad component profiles of [O iii] λ5008 as a template for collisionally excited lines. The broad component areas overlap with the narrow profile such that the broad components are responsible for 8.6% and 2.2% of the narrow-component flux, or 10.8% in total. We use this fraction to set the upper contamination limit of potential broad components to the UV emission lines and determine the impact on nebular density, temperature, and abundance calculations in Section 4.4.\r\n\r\n2.3. Reddening Correction\r\nThe observed Balmer decrement of the narrow Hα/Hβ lines is FHα/FHβ = 3.48, implying either a moderate amount of dust is present or collisional enhancement of Hα. This value disagrees with the results of M. W. Topping et al. (2024), who measured an observed decrement of 2.55 ± 0.05 that they found to be consistent with no dust attenuation. Similarly, A. Crespo Gómez et al. (2025) used high-resolution NIRSpec/G395H data to fit multiple component Balmer decrements for RXCJ2248-ID3, finding a narrow-component FHα/FHβ = 2.7 that is consistent with no attenuation, but broad- and very broad-component decrements of 4.3 and 6.6, respectively, that imply differential extinction. We too find higher FHα/FHβ ratios for the broad components, but the source of this increase is not clear; it could indicate higher dust in the broad component gas, as suggested by A. Crespo Gómez et al. (2025), or result from significant collisional enhancement of Hα.\r\n\r\nFortunately, the GLIMPSE-D spectrum provides a significant increase in S/N in the continuum, allowing for more robust fitting of broad components, including in the Hγ and [O iii] λ4364 and λ5008 lines. Fitting the broad components directly in the [O iii] lines offers the advantage over previous works that we do not need to correct for broad component contamination with differential extinction in our Te calculation. Furthermore, by fitting the broad components in Hγ we were able to examine the narrow-component Hβ/Hγ ratio, finding a decrement of FHβ/FHγ = 2.16 that is consistent with very little dust (see Table 2). Note that we do not consider the Hβ/Hδ ratio here because the Hδ line is not strong enough to robustly fit the broad components in a consistent manner with the profile fitting of the Hγ, Hβ, and Hα lines.\r\n\r\nTable 2. Rest UV+Optical Emission-Line Fluxes\r\n\r\nIon+Wavelength\tI(λ)/I(C iii])\tEW\r\n(Å)\t \t(Å)\r\nN iv] λ1483.33\t42.78 ± 1.61\t6.67\r\nN iv] λ1486.50\t102.0 ± 0.82\t15.9\r\nHe iiλ1640.42\t22.46 ± 197\t4.88\r\nO iii] λ1666.15\t85.84 ± 0.59\t18.9\r\nN iii] λ1750a\t38.59 ± 0.64\t9.18\r\nSi iii] λ1883.00\t5.01 ± 3.25\t1.32\r\nSi iii] λ1892.03\t8.25 ± 1.98\t2.21\r\nC iii] λ1906.68\t35.11 ± 0.31\t9.65\r\n[C iii] λ1908.73\t64.89 ± 0.25\t17.9\r\nIon+Wavelength\tI(λ)/I(Hβ)\tEW\r\n(Å)\t \t(Å)\r\n[O ii] λ3728a\t4.09 ± 2.05\t6.22\r\nHγ λ4341.66b\t47.41 ± 3.07\t73.8\r\n[O iii] λ4364.44b\t42.45 ± 1.92\t66.5\r\nHe i λ4472.73\t8.90 ± 0.39\t27.8\r\nN iii λ4641.94\t1.40 ± 0.20\t4.4\r\nHe ii λ4687.01\t1.33 ± 0.29\t4.2\r\n[Ar iv] λ4712.69c\t2.30 ± 0.27\t10.3\r\nHe i λ4714.46c\t1.91 ± 0.19\t3.0\r\n[Ar iv] λ4741.49\t4.10 ± 0.26\t13.0\r\nHβ λ4862.71b\t100.0 ± 4.4\t356\r\n[O iii] λ4960.29b\t230.5 ± 9.0\t877\r\n[O iii] λ5008.24b\t708.9 ± 27.5\t2791\r\nHα λ6564.60b,d\t331.8 ± 14.4\t1755\r\nHα λ6564.60b,e\t274.1 ± 11.9\t1457\r\n[N ii] λ6585.27\t7.08 ± 0.91\t12.8\r\n[S ii] λ6718.29\t0.68 ± 0.29\t4.78\r\n[S ii] λ6732.67\t0.81 ± 0.30\t4.74\r\nE(B − V)\t\t⋯\r\nFC III]\t11.58 ± 0.49\t⋯\r\nb\t6.94 ± 0.15\t⋯\r\nNotes. Reddening-corrected emission-line intensities of lines used in this analysis from the archival rest-UV and GLIMPSE rest-optical JWST/NIRSpec spectra for RXCJ2248-ID3. Note that no scaling was performed between the archival UV and GLIMPSE-D optical pointings (not needed for this work). Thus, UV fluxes are given relative to the FC III]λλ1907,09 × 100 and optical fluxes are given relative to FHβ × 100. The last three rows list the dust attenuation derived using the J. A. Cardelli et al. (1989) reddening law and the rest-frame C iii] λλ1907,09 and Hβ flux in units of 10−18 erg s−1 cm−2. Additionally, the fluxes reported here are for a single image of RXCJ2248 (ID3), whereas M. W. Topping et al. (2024) report fluxes for coadded spectra of multiple images. aNote that N iii] λ1750 and [O ii] λ3728 fluxes are the integrated values for the N iii] λλ1746,1748,1749,1752,1754 quintuplet and [O ii] λλ3727,3730 doublet, respectively. bEmission-line profile was best fitted with a narrow Gaussian and two broad Gaussian components; only the corrected narrow-line flux is listed here (see Section 2.2 and Figure 3). c[Ar iv] λ4713+He iλ4714 is a blended line profile at the observed resolution. Thus, the [Ar iv] λ4713 is determined by subtracting the He iλ4714 flux, which is predicted from the He i λ4473 flux. dUncorrected for collisional excitation. eCorrected for collisional excitation.\r\n\r\nDownload table as: \r\nASCIITypeset image\r\n\r\nThe reddening due to dust, characterized by E(B − V), was determined by comparing the observed Balmer decrements with the theoretical Balmer ratios assuming case B and an extinction law, for which we tested the parameterization from both J. A. Cardelli et al. (1989) and D. Calzetti et al. (2000). The E(B − V) value for a given Balmer ratio was determined iteratively until convergence, recomputing the H i theoretical ratio using the updated electron temperature from the reddening-corrected [O iii] λ4364/λ5008 flux ratio and density from the reddening-corrected N iv] λ1483/λ1487 flux ratio in each iteration. In this way, the reddening, electron temperature, and electron density were solved for simultaneously and consistently.\r\n\r\nA greater enhancement of the observed FHα/FHβ decrement than of the FHβ/FHγ decrement can arise under high-density conditions, where collisional excitation selectively enhances the lowest excited level (n = 2; requires lowest energy to excite), leading to higher Hα flux relative to Hβ and Hγ. To assess whether such an enhancement is physically plausible, we examined the Cloudy photoionization models (M. Chatzikos et al. 2023; C. M. Gunasekera et al. 2023) presented in Z. Martinez et al. (2025), which span a wide range of nebular densities (up to ne = 109 cm−3). For the nebular conditions determined in this work (i.e., Te, , Z, N/O; see Section 4), densities of ne ∼ 106 cm−3 are needed to produce the observed Hα enhancement while minimally affecting Hβ and Hγ. Although this density is roughly an order of magnitude higher than the values measured in M. W. Topping et al. (2024) and in this study (see Section 4.1 and Table 3), it could indicate that the interstellar medium (ISM) contains unresolved clumps of even higher density than the volume-weighted values probed by the density diagnostics used in this work. We, therefore, attribute the observed Hα excess to collisional enhancement.\r\n\r\nTable 3. Nebular Conditions and Abundances for RXCJ2248-ID3\r\n\r\nProperty\tIon. E\tUsed\tValue\r\n \t(eV)\t \t \r\nTemperatures:\t \t \r\nTe,high meas. (K)\t35.11–54.93\tne(N+3)\t1.97 ± 0.03 × 104\r\nTe,int. used (K)\t23.33–34.83\tD. R. Garnett (1992)\t1.81 ± 0.02 × 104\r\nTe,low used (K)\t13.62–35.11\tD. R. Garnett (1992)\t1.68 ± 0.02 × 104\r\nDensities:\t \t \t \r\nne(N+3) (cm−3)\t47.45–77.47\tTe,high\t\r\nne(Ar+3) (cm−3)\t40.74–59.81\tTe,high\t\r\nne(C+2) (cm−3)\t24.38–47.89\tTe,int.\t\r\nne(Si+2) (cm−3)\t16.35–33.49\tTe,int.\t\r\nne(S+) (cm−3)\t10.36–23.33\tTe,low\t\r\nO Abundances:\r\nO+/H+ (×10−5)\t13.62–35.11\tTe,low; ne(Si+2)\t0.186 ± 0.148\r\nO+2/H+ (×10−5)\t35.11–54.93\tTe,high; ne(Ar+2)\t5.473 ± 0.261\r\n \t \t7.753 ± 0.023\r\nIonization Parameters:\r\nlogUint.(O32)\t13.62–54.93\tne = 104 cm−3\t−1.24 ± 0.23\r\nlogUhigh(N43)\t29.60–77.47\tne = 105 cm−3\t−0.69 ± 0.10\r\nN Abundances:\r\nN+3/O+2\t47.45–77.47\tTe,high; ne(N+3)\t0.277 ± 0.043\r\nN+2/O+2\t29.60–47.45\tTe,high; ne(C+2)\t0.145 ± 0.070\r\nN+/O+\t14.53–29.60\tTe,low; ne(Si+2)\t0.367 ± 0.259\r\nICF(N+3/O+2)\t47.45–77.47\tTe,high; ne(N+3)\t1.542\r\nICF(N+2/O+2)\t29.60–47.45\tTe,high; ne(C+2)\t2.547\r\nICF(N+/O+)\t14.53–29.60\tTe,low; ne(Si+2)\t0.814\r\nlog(N/O)\t⋯\t⋯\t−0.368 ± 0.062\r\nlog(N/O)\t⋯\t⋯\t−0.434 ± 0.071\r\nlog(N/O)\t⋯\t⋯\t−0.525 ± 0.257\r\nlog(N/O)all\t⋯\t⋯\t−0.375 ± 0.056\r\n⋯\t⋯\t−0.390 ± 0.035\r\nC Abundance:\r\nC+2/O+2\t24.38–47.89\tTe,int; ne(C+2)\t0.107 ± 0.014\r\nICF(C+2/O+2)\t24.38–47.89\tTe,int; ne(C+2)\t1.498\r\nlog(C/O)\t \t \t−0.795 ± 0.052\r\nSi Abundance:\r\nSi+2/O+2\t16.35–33.49\tTe,low; ne(Si+2)\t0.005 ± 0.001\r\nICF(Si+2/O+2)\t16.35–33.49\tTe,low; ne(Si+2)\t3.507\r\nlog(Si/O)\t⋯\t⋯\t−1.781 ± 0.157\r\nNote. Ionic and total abundances for RXCJ2248-ID3. Column (1) lists the property, while Column (2) lists the associated ionization potential energy range (eV), Column (3) lists the temperature and/or density used in the calculation, and Column (4) provides the final values. All calculations reported here only used the narrow components when multicomponent fits were performed. Note that the temperatures for the intermediate- and low-ionization zones were inferred from Te,high using the Te–Te relationships of D. R. Garnett (1992). Two ionization parameters are reported for the O32 and N43 indicators from Z. Martinez et al. (2025). The oxygen abundance was determined using the archival [O ii] λ3728 detection and the new [O iii] λ5008 fit. N/O was determined using four different ion+ICF (from Z. Martinez et al. 2025) combinations: (1) optical N+/O+; (2) UV N+2/O+2; (3) UV N+3/O+2; and (4) combination (N++N+2+N+3)/(O++O+2). C/O and Si/O were determined from the archival UV emission lines only.\r\n\r\nDownload table as: \r\nASCIITypeset image\r\n\r\nAccordingly, we adopted the reddening derived from Hγ/Hβ, mag using J. A. Cardelli et al. (1989) (the D. Calzetti et al. (2000) value is similar at E(B − V) = 0.050 ± 0.1215 mag), and corrected all emission lines for the resulting (minimal) dust attenuation. We used the D. Calzetti et al. (2000) reddening law for the rest-UV emission lines (λ < 3200 Å) and the J. A. Cardelli et al. (1989) reddening law for the rest-optical emission lines (λ > 3200 Å). After applying the reddening correction, the Hα/Hβ ratio still shows a collisional excess of 0.204 above the theoretical value; we correct for this excess and report a final FHα = 1.985 × 10−17 erg s−1 cm−2.\r\n\r\nThe adopted reddening and dereddened line intensities are listed in Table 2 for all line fluxes used in this work. Note that rest-UV and rest-optical lines should not be compared or combined in line ratios. Since the rest-UV and rest-optical spectra were obtained during different observing runs with distinct pointings and strategies, we report the UV lines relative to FCIII]λλ1907,1909 × 100 and the optical lines relative to FHβ × 100, without applying any relative scalings between the two datasets.\r\n\r\n3. Wolf Rayet Stars at z = 6.1\r\nThe WR stage of massive star evolution is an important, short-lived phase that can have significant effects on the chemical composition of the local ISM. We provide a brief overview here (see, e.g., P. A. Crowther 2007, for a more thorough review). WR stars are massive stars that have entered the core He-burning phase and have lost their outer envelope either via strong stellar winds or due to binarity effects (i.e., stripping via Roche Lobe overflow or mergers). The first phase of WR stars occurs when the outer H layer has been ejected, revealing the H core-burning products such that their spectra are characteristically He and N rich but are H-poor. Such stars are known as nitrogen-type WR, or WN, stars, and are often identified by strong N iii, N iv, and N v emission lines, especially the broad optical “blue bump” near λ4650. The blue bump is a complex of features, including N iii λλ4634,4642, C iii λ4649,4667, Fe iii λ4660, and He ii λ4687. Subsequently, stars that are massive enough for core He-burning and for their winds to remove their outer He envelope and expose the produced C enter the WR carbon (WC) phase. WC stars also have strong, broad He ii emission and strong C and O emission, such that they are identified by the optical WR C iv λλ5803,5814 doublet (the “red bump”). As a result, the typically very strong winds of the WR phase can produce significant N enrichment during the WN phase and drive strong C ejection during the WC phase. After the WC phase, a WR-oxygen phase may ensue, but we forgo discussion of this phase here.\r\n\r\nThe rest-frame UV and optical spectra shown in Figure 2 can be used to characterize the WR nature of the stellar population in RXCJ2248-ID3. Both the UV and optical He ii emission features are kinematically broadened compared to the narrow nebular emission features in RXCJ2248-ID3, indicative of WR or VMS winds. F. Martins et al. (2023, 2025) have shown that young star-forming regions dominated by VMSs can be distinguished from WR stars using the morphology of the blue and red bumps. In particular, VMSs produce blue bumps with He ii λ4687 emission but little to no N iii emission and red bumps with narrow C iv λλ5803,5814 emission. Thus, strong detections of N iii in the blue bump favor a WN interpretation (e.g., F. Martins et al. 2023; D. A. Berg et al. 2024; T. E. Rivera-Thorsen et al. 2024).\r\n\r\nThe upper right-hand panel of Figure 2 highlights the blue bump spectral regime, showing weak, broad He ii and N iii λ4642 in RXCJ2248-ID3, both of which are characteristic of metal-poor WN stars. Just redward of the N iii λ4642 line in the blue bump (but blueward of [Fe iii]), a second less prominent emission feature is seen, but it is difficult to determine whether this is due to C iii or O ii emission, or both. Furthermore, the red C iv bump is not detected, suggesting little to no contributions from WC stars or VMSs in the spectrum. Thus, we only significantly detect the blue WR bump, suggesting that WN stars are likely present.\r\n\r\n4. Nebular Properties\r\nUsing the updated narrow-component emission-line fits presented in Section 2.2, we determined the nebular properties of RXCJ2248-ID3. Following D. A. Berg et al. (2021), we adopt the four-zone ionization model to account for the high-ionization emission observed. In this model, the ionization potential energy ranges of N+, S+2, O+2, and He+2 define the low-, intermediate-, high-, and very high-ionization zones, respectively. For all calculations, we use the PyNeb package in Python with the atomic data adopted in D. A. Berg et al. (2019), which includes a six-level atom model for oxygen in order to utilize the UV O iii] λ1666 line. Below, we determine temperatures and densities, although Te(O+2) and ne(N+3) were codetermined during the iterative reddening calculation (see Section 2.3) in Section 4.1, ionization parameters in Section 4.2, and abundances in Section 4.3.\r\n\r\nWe note that the UV spectra do not have sufficient S/N to decompose narrow and broad components following the same method as the optical lines. As a result, density diagnostics and abundances determined from UV lines may include contributions from multiple kinematic components, while optical temperatures, densities, and abundances are derived from narrow components alone. If the broad component arises from gas with distinct physical conditions, this could introduce systematic offsets. For this reason, we examine the potential impact of UV broad components in Section 4.4.\r\n\r\n4.1. Temperature and Density\r\nOne of the unique characteristics of RXCJ2248-ID3 is its large number of density-sensitive emission-line ratios. M. W. Topping et al. (2024) previously reported densities from the three UV line ratios of Si iii] λ1883/λ1892, characterizing the intermediate-ionization zone, C iii] λ1907/λ1909, characterizing the intermediate- to high-ionization zone, and N iv] λ1483/λ1486, characterizing the high- to very high-ionization zone. The new high-S/N optical spectra enables us to measure, for the first time, densities from the low-ionization [S ii] λ6717/6731 ratio and the high- to very high-ionization [Ar iv] λ4713/λ4741 ratio.\r\n\r\nWe use our narrow-component dereddened flux measurements to compute densities for all five line ratios and the high-ionization zone temperature from the [O iii] λ4364/λ5008 ratio. The high-ionization zones Te(O+2) and ne(N+3) were simultaneously determined during the iterative reddening calculation in Section 2.3 to account for the sensitivities of both diagnostics. If the low density limit was assumed instead (ne ≲ 102 cm−3), as is common practice at low-redshift, the observed [O iii] λ4364/λ5008 flux ratio would lead to unphysical temperatures (i.e., above the limit set by H cooling of ∼2.5 × 104 K). Thus, a physical and robust solution requires high densities to properly account for the reduced λ5008 flux due to collisional de-excitation. Furthermore, Z. Martinez et al. (2025) recently showed that densities derived from both optical and UV diagnostics underpredict the true volume-averaged density in multiphase, high-density systems, with more severe underprediction from the optical diagnostics. Therefore, it is necessary to use UV density diagnostics in high-density environments, though the true density will still be underestimated in multiphase gas (see, e.g., Figure 11 of Z. Martinez et al. 2025).\r\n\r\nFor the high-ionization zone, we found a Te(O+2) = 1.97 ±0.03 × 104 K and ne(N+3) cm−3, which is consistent with the density of ne(N+3) cm−3 reported by M. W. Topping et al. (2024), but lower than their temperature of 2.46 ± 0.26 × 104 K due to our broad component fits of both [O iii] λ4364 and λ5008. Adopting our Te(O+2) as the high-ionization temperature (Te,high), we then applied the Te–Te relations of D. R. Garnett (1992) to estimate the intermediate-ionization temperature (Te,int.) and low-ionization temperature (Te,low).\r\n\r\nThe determined temperatures were used for the subsequent density calculations in their respective ionization zones. Note that the [Ar iv] λ4713 and He i λ4714 lines are blended in the G395M grating. Therefore, we corrected the [Ar iv] λ4713 flux for the He i λ4714 contribution, predicting the He i λ4714 flux from the measured He i λ4473 flux and the theoretical He i λ4714/λ4473 ratio (∼0.21 for the conditions in RXCJ2248-ID). The resulting densities, all of which fall within their respective diagnostic ranges, and temperatures are reported in Table 2.\r\n\r\nRemarkably, RXCJ2248-ID3 is one of few galaxies, and the only galaxy yet at high redshifts, to have significant (>3σ) electron density measurements from five different ions that span a large ionization range (∼10–77 eV). Furthermore, the densities in RXCJ2248-ID3 appear to be organized into an interesting nebular stratification. The UV emission lines trace the densest gas, with ne(N+3) = 2.65 × 105 cm−3 in the highest-ionization gas, followed by ne(C+2) = 7.94 × 104 cm−3 and ne(Si+2) = 4.77 × 104 cm−3. In contrast, the optical high-ionization lines are emitted from regions of lower densities: the optical [Ar iv] diagnostic has an overlapping ionization energy range with the UV N iv] diagnostic but a density that is an order of magnitude lower.\r\n\r\nThere are two possible interpretations of the measured array of densities. First, since the UV lines also have higher excitation energies, they could originate preferentially from hotter, denser clumps. This would imply a strongly inhomogeneous ISM, in which compact, high-pressure structures dominate the UV line emission while somewhat more diffuse gas produces much of the optical emission. Alternatively, the multiphase ISM may span a smaller dynamic range of densities than we measure due to the suppression of the optical diagnostics. Z. Martinez et al. (2025) showed that for an ISM with a mix of low- (e.g., 103 cm−3) and high-density gas (e.g., 105 cm−3) that has a true volumetric density that is somewhere in between, the low-ionization optical diagnostics will always be significantly biased low, close to the low-density gas value, until the fraction of high-density gas is very high (e.g., >95%). This effect occurs when ne-diagnostic line ratios have low critical densities (e.g., ne,crit([S ii])≈2 × 103–5 × 103 cm−3), such that emission from the high-density gas is collisionally suppressed beyond detection. The magnitude of this effect decreases with increasing critical density such that [S ii] is significantly affected, [Ar iv] is moderately affected (ne,crit ≈ 2 × 104–2 × 105 cm−3), and the UV Si iii], C iii], and N iv] (ne,crit ≈ 5 × 104–5 × 1010 cm−3) are minimally affected, albeit still biased low. In this scenario, there would still be density stratification, but with smaller differences.\r\n\r\nAll together, the nebular diagnostics in RXCJ2248-ID3 support a picture of a multiphase nebula with density and temperature stratification, likely reflecting a clumpy ISM shaped by the feedback and local radiation field variations of bursty star formation (see, also, N. Choustikov et al. 2025; Y. Harikane et al. 2025b; M. Usui et al. 2025). This picture is also consistent with the density stratification that has been reported for dwarf galaxies both near and far (e.g., B. L. James et al. 2016; D. A. Berg et al. 2021; M. Mingozzi et al. 2022; X. Ji et al. 2024; M. W. Topping et al. 2024), but with typical densities increasing with redshift (e.g., Y. Isobe et al. 2023; Abdurro’uf et al. 2024; Z. Martinez et al. 2025; M. W. Topping et al. 2025a).\r\n\r\n4.2. Ionization Parameter\r\nThe ionization parameter of RXCJ2248-ID3, , determined using the typical O32 = Iλ5008/Iλ3728 diagnostic is reported in M. W. Topping et al. (2024) to be in the high range of to −1. We recompute the ionization parameter for RXCJ2248-ID3 using the O32 and N43 = Iλλ1483,1486/Iλ1750 diagnostics from Z. Martinez et al. (2025) that are calibrated for densities in the 102 ≤ ne(cm−3) ≤ 106 range. We estimate a using O32, which is consistent with the value reported by M. W. Topping et al. (2024), and using N43. Note, however, that the O32 diagnostic is very sensitive to the assumed density (Z. Martinez et al. 2025), making this value highly uncertain in dense gas. For example, densities of ne = 103–105 cm−3 would lead to a range of to −2.04, respectively.\r\n\r\n4.3. Abundances\r\nHere, we present direct-method abundances of oxygen-to-hydrogen (O/H) (Section 4.3.1), N/O (Section 4.3.2), carbon-to-oxygen (C/O) (Section 4.3.3), and silicon-to-oxygen (Si/O) (Section 4.3.4) for RXCJ2248-ID3 using narrow-line flux ratios and the measured temperatures and densities presented in Section 4.1. Nearly all of the optical lines used in this work have sufficient S/N to simultaneously constrain broad and narrow emission components, but there are a few exceptions, all of which are low-ionization lines. The [O ii] λ3728 line was not covered by the GLIMPSE-D spectrum and so lacks the S/N to fit broad components. Both [N ii] λ6585 and [S ii] λλ6718,6733 are covered in the high-S/N GLIMPSE-D spectrum but are either blended with stronger features or too weak to fit broad components. On the other hand, the [O ii] and [S ii] lines have low critical densities around ne,crit ∼ 103 cm−3 such that any moderate to high-density broad components are likely collisionally de-excited away. Their narrow-component fluxes could also be significantly reduced by collisional de-excitation; however, the missing [O ii] emission is likely small in the absolute sense for such a high-ionization object. Emission from [N ii] is less likely to be collisionally de-excited (ne,crit ∼ 105 cm−3), so a hidden broad component could lead to an overestimate of the N/O abundance, but this effect would be somewhat countered by the underestimated [O ii] flux. In the end, the consistency of N/O derived independently from UV and optical tracers in Section 4.3.2 below suggests that these effects do not significantly impact our results.\r\n\r\nTo calculate the total or relative abundance of an element, we determine and sum the individual observed ions and then apply an ionization correction factor to account for unseen prominent ionization states. The abundance of an individual ionic species, Xi, relative to hydrogen is determined as\r\n\r\nwhere jλ(i) is the emissivity determined for the appropriate ionization zone temperature and density. Given the tendency of the optical density diagnostics to severely underestimate the density in high-density environments, we instead adopt the UV-derived densities. Note that the abundances presented below have not been corrected for the fraction of atoms embedded in dust. However, the level of depletion onto dust grains is expected to be small for the low metallicity of RXCJ2248-ID3 (e.g., A. Rémy-Ruyer et al. 2014; F. Galliano et al. 2018; J. Roman-Duval et al. 2022). Y. Isobe et al. (2026) also infer negligible dust depletion for RXCJ2248-ID3 based on the high value of Si/O that that they determine, but this is inconsistent with the value we determine below. Details of elemental abundance determinations are given below.\r\n\r\n4.3.1. Oxygen Abundance\r\nWe determine the total O/H abundance as the sum of the O+/H+ and O+2/H+ ionic abundances, determined from the [O ii] λ3728 and [O iii] λλ4960,5008 optical emission lines. We observe no strong O0 or O+3 emission, indicating that contributions from other ions are negligible. The resulting ionic and total oxygen abundances are presented in Table 2. Similar to M. J. Hayes et al. (2025) and Z. Martinez et al. (2025), we find that one of the most significant effects of accounting for high densities is the resulting decrease in electron temperature and subsequent increase in oxygen abundance (see, also, H. Katz et al. 2023). In our work, this results both from accounting for the missing [O iii] λ5008 flux due to collisional de-excitation and from correcting the narrow emission for broad emission components at their base. M. W. Topping et al. (2024) also incorporated the high densities seen in RXCJ2248-ID3 but did not have the S/N to fit the broad emission components in both [O iii] λ5008 and λ4364. As a result, we measure an oxygen abundance of . Note that if unresolved high-density clumps (ne ≳ 105 cm−3) are present (as suggested in, e.g., Section 2.3), it could introduce additional uncertainty by biasing the luminosity-weighted [O iii] λ4364/λ5008 ratio to higher densities, which would drive the derived Te higher and O/H abundance lower. However, Z. Martinez et al. (2025, see Figure 11), showed that the use of high-critical density UV density diagnostics largely mitigate this effect in a density stratified medium.\r\n\r\n4.3.2. Relative N/O Abundance\r\nThe extraordinary simultaneous detections of [N ii] λ6585, N iii] λ1750, and N iv] λλ1483,1487 enable multiple determinations of the N/O abundance. Therefore, we calculate N/O abundances using four different ionic methods\r\n\r\n\r\n\r\n\r\nwhere [O ii] λ3728 is used for the N+/O+ determination, O iii] λ1666 is used for the N+2/O+2 and N+3/O+2 calculations, and X(N+i) and X(O+i) are the N and O ionization fractions, respectively. We use the density-dependent ICFs from Z. Martinez et al. (2025), who provide prescriptions for densities of ne = 102, 103, 104, 105, and 106 cm−3. We, therefore, round our density measurements to the nearest order of magnitude and use the intermediate-ionization for the N+/O+ ICF and the high-ionization for the N+2/O+2 and N+3/O+2 ICFs. The resulting N ICFs and N/O abundances are reported in Table 3.\r\n\r\nThe four N/O determinations of RXCJ2248-ID3 are in close agreement, far above the expected value for its metallicity. Visually, this is shown in the upper left-hand panel of Figure 4, which plots the relative N/O versus O/H abundance with RXCJ2248-ID3 marked by purple diamonds. The traditional N/O–O/H trend has been established by many z ∼ 0 studies of H ii regions and galaxies (gray points: C. Esteban et al. 2002, 2009, 2014; L. S. Pilyugin & T. X. Thuan 2005; L. van Zee & M. Haynes 2006; J. García-Rojas & C. Esteban 2007; Á. R. López-Sánchez et al. 2007; D. A. Berg et al. 2012, 2016,2019, 2020). The empirical trend is a bimodal relationship, with a flat trend due to primary (or metallicity-independent) N production at low metallicities () and an increasing N/O trend with O/H as secondary (or metallicity-dependent) N production becomes increasingly important at higher metallicities (). As a visual guide, the primary N/O plateau from D. A. Berg et al. (2019, dashed purple line) is shown and the empirical stellar curve from D. C. Nicholls et al. (2017, solid green line) is shown as an example of the full primary and secondary curve.\r\n\r\nZoom InZoom OutReset image size\r\nFigure 4. Relative C and N abundance trends versus metallicity. Nitrogen to oxygen ratio versus oxygen abundance for star-forming galaxies is plotted in the left panels, while C/O ratio versus oxygen abundance is plotted in the middle panels, and carbon to nitrogen abundance versus oxygen abundance is plotted in the right panels. Top row: RXCJ2248-ID3 is shown relative to the observed z ∼ 0 trend and other high-z galaxies. The abundances for RXCJ2248-ID3 are shown as purple diamonds, where multiple N/O points show the measurements for each ionic N/O calculation method. For comparison, we also plot the abundances derived for RXCJ2248-ID3 by M. W. Topping et al. (2024) as turquoise squares. The typical bimodal N/O trend is characterized by local dwarf (gray diamonds; L. van Zee & M. Haynes 2006; D. A. Berg et al. 2012, 2016, 2019) and spiral galaxy (gray circles; C. Esteban et al. 2002, 2009, 2014; L. S. Pilyugin & T. X. Thuan 2005; J. García-Rojas & C. Esteban 2007; Á. R. López-Sánchez et al. 2007; D. A. Berg et al. 2020) H ii region measurements. The primary N/O plateau from D. A. Berg et al. (2019) is shown as a dashed purple line, while the solid green line is the empirical stellar curve from D. C. Nicholls et al. (2017). Additional C/O literature measurements for dwarf galaxies are from M. A. Peña-Guerrero et al. (2017) and P. Senchyna et al. (2017). Abundances for z > 2 galaxies from Z. Martinez et al. (2025) are plotted as blue plus signs for galaxies with UV N+2/O+2 derived abundances and pentagons for optical N+/O+ derived abundances. Bottom row: The same observed samples are shown as the top row, but with the z ∼ 0 sample represented by the shaded gray regions. The observed abundances of RXCJ2248-ID3 are compared to updated dual-burst chemical evolution models of C. Kobayashi & A. Ferrara (2024, string of circles), color coded by age since onset of the second burst. The models have been modified to reproduce both the enhanced N/O and relatively deficient C/O observed for RXCJ2248-ID3, which requires enrichment from WN but very little WC enrichment, as expected at low metallicities.\r\n\r\nDownload figure:\r\n\r\nStandard imageHigh-resolution image\r\nFor comparison, we plot the high-quality high-redshift N/O measurements that were calculated in a consistent manner as the present work (with direct-method Te and ne determinations and ne-dependent ICFs) by Z. Martinez et al. (2025). N/O abundances determined using N+2/O+2 are plotted as blue + symbols, while N+/O+ determinations are plotted as blue pentagons. Of these galaxies, the closest comparison to RXCJ2248-ID3 is CEERS-1019 (see, also, R. Marques-Chaves et al. 2024), while only GDS 3073 and GN-z11 have higher relative N/O abundances and only GDS 3073 is more enhanced in N/O for its O/H abundance.\r\n\r\nWe find that all four ionic methods produce consistently high N/O values within their uncertainties, with a weighted mean of . This is an important result because RXCJ2248-ID3 is the first galaxy to have consistently enhanced N/O abundances measured from both the rest-frame UV high-ionization and the optical low-ionization emission lines. Furthermore, measuring consistent N/O values from three different ionic methods strengthens our confidence in the robustness of the N/O measurement, although uniform N/O across the ionization structure of the nebula is not a given in a stratified medium. While there is strong evidence for a stratified, or perhaps very clumpy, density structure in RXCJ2248-ID, the N/O abundance appears to be well mixed.\r\n\r\n4.3.3. Relative C/O Abundance\r\nMeasuring the C/O abundance provides a crucial comparative baseline for interpreting the origin of elevated N/O in RXCJ2248-ID3. Similar to N, C has a pseudosecondary17 production pathway, but the dominant nucleosynthetic sources and timescales differ for C and N. Briefly, both C and O are primarily produced in massive stars (>8 M⊙) on relatively short timescales such that the C/O ratio is a relatively stable tracer of massive star yields, although some C is produced via low- to intermediate-mass AGB stars (∼1.5–3 M⊙). In contrast, some N is produced by massive stars (e.g., through rotational mixing and WR winds) but most N comes from intermediate-mass AGB stars (∼4–8 M⊙), which release N on longer timescales (∼200 Myr). Therefore, N/O and C/O together serve as diagnostics of the recent star formation history, constraining the recent enrichment mechanisms of galaxies (e.g., D. R. Garnett 1990; R. B. C. Henry et al. 2000; C. Chiappini et al. 2003; E. Pérez-Montero & T. Contini 2009; D. A. Berg et al. 2019; E. Pérez-Montero et al. 2021).\r\n\r\nRelative C/O abundances are typically determined using the C iii] λλ1907,1909/O iii] λ1666 ratio to calculate C+2/O+2 and assuming that C/O ≈ C+2/O+2. This method is sometimes used alone owing to the fact that (1) C+2 and O+2 have somewhat similar ionization potentials (24.38 and 35.12 eV, respectively), (2) the upper levels of the λ1666 and λλ1907,1909 transitions have similar excitation potentials (∼6.5 and ∼7.5 eV, respectively), and (3) the integrated fluxes of λ1666 and λλ1907,1909 are not sensitive to collisional de-excitation for the densities measured here. However, for the high-ionization nebulae in RXCJ2248-ID3, it is important to account for contributions from the C+3 species and any unseen species. We note that the C iv λλ1548,1550 doublet is clearly observed in the rest-UV spectrum of RXCJ2248-ID3, but these lines are resonant and can be affected by the C iv stellar wind feature and ISM absorption, and so determining the intrinsic flux and subsequent C+3 abundance is challenging. Instead, we use an ICF determined from the photoionization models presented in Z. Martinez et al. (2025) such that\r\n\r\nWe used the and a density of ne(C+2) ∼ 105 cm−3 to determine the C ICF. The resulting C ICF and C/O abundance are reported in Table 3.\r\n\r\nThe C/O and C/N abundances for RXCJ2248-ID3 are plotted in the upper middle and right-hand panels of Figure 4. Empirical trends of C/N at z ∼ 0 are found to be flat, albeit with significant scatter (see shading in Figure 4), suggesting that the dominant nucleosynthetic mechanisms of C are similar to those of N (e.g., D. R. Garnett et al. 1999; C. Esteban et al. 2014; D. A. Berg et al. 2016, 2019). However, while the production of both C and N appear to be metallicity-dependent, the scatter in their trend is consistent with differing production timescales due to stars of different masses. Thus, the variations observed in CNO abundance patterns of high-redshift galaxies may be the result of taking a snapshot of many galaxies at different times since their most recent onset of star formation.\r\n\r\nRXCJ2248-ID3 appears to have a similar CNO abundance pattern to other high-redshift N emitters, characterized by enhanced N/O but relatively deficient C/O such that their C/N is very deficient compared to the expectations from low-redshift trends. This suggests that these high-redshift N-emitting galaxies are enhanced in N relative to both O and C. If massive stars in the WN phase are present, they will have recently produced 14N at the expense of 12C through the CNO cycle, meaning C used as a catalyst in the cycle initiation will have been consumed as N is removed during the bottleneck step via dredged up, preventing the return of C at cycle completion. Thus, C/N-deficiency is consistent with a recent, intense episode of N enrichment and C consumption from WN stars. Conversely, if both N/O and C/O were elevated in tandem, it could point to broader enrichment by massive stars, such as enrichment from both WN and WC stars, whose contributions increase at higher metallicities.\r\n\r\n4.3.4. Relative Si/O Abundance\r\nDetecting Si iii] λλ1883,1892 in RXCJ2248-ID3 enables the rare opportunity to measure the silicon-to-oxygen (Si/O) abundance in a z > 5 galaxy (see, also, Y. Isobe et al. 2026, for Si/O in GN-z11). Silicon abundances are important for multiple reasons. Silicon is highly refractory, making the Si/O ratio a sensitive probe of dust depletion. Additionally, Si probes different channels of chemical enrichment than CNO elements, as it is primarily an α-element produced by CCSNe, but Type Ia SNe, AGB stars, and even pair-instability SNe are all expected to contribute to the total Si abundance. For RXCJ2248-ID3 we determine the Si/O abundance using the observed Si iii] λλ1883,1892/O iii] λ1666 ratio to calculate Si+2/O+2. Because Si+2 and O+2 have rather different ionization potentials (16.3 eV versus 35.1 eV, respectively), a Si ICF is required to convert Si+2/O+2 to total Si/O via\r\n\r\nSi ICFs have been reported previously (e.g., D. R. Garnett et al. 1995), but none account for the high-density conditions observed in RXCJ2248-ID3. Therefore, we determined a Si ICF = 3.507 using the photoionization models presented in Z. Martinez et al. (2025) using the and a density of ne(Si+2) ∼ 104 cm−3. Reported in Table 3, the resulting (Si/O) = −1.781 ± 0.157 abundance is typical of metal-poor dwarf galaxies (e.g., D. R. Garnett et al. 1995; Y. I. Izotov & T. X. Thuan 1999), consistent with normal massive star production and low dust depletion.\r\n\r\n4.4. Potential Impact of UV Broad Components\r\nThe exceptionally high S/N of the rest-optical GLIMPSE-D spectrum allows for broad emission component fits that the rest-UV spectrum does not. In Section 2.2, we found the broad emission component contribution to the narrow [O iii] λ5008 flux to be 10.8%. To examine the possible effects such contamination has on calculations of nebular conditions and abundances, we adopt 10.8% as the contamination upper limit to the UV emission lines. We first consider the impact on the UV density determinations, where we allow the broad components of the UV density-sensitive emission-line ratios to have densities ranging from 102–106 cm−3. After subtracting the potential broad component contribution, the revised densities change up to Δne(Si+2), Δne(C+2), and Δne(N+3) over the range of broad component densities considered. These values are within the reported uncertainties in Table 3, with the exception of the ∼1.2σ deviation for Δne of C+2.\r\n\r\nNext, we tested the subsequent impact of UV densities that have been revised for possible broad components on the properties determined from rest-optical emission lines: Te(O+2), O/H, and N/O. For the range of Δne(N+3) above, the resulting K, which is within 1σ–2σ of the reported value in Table 3. Similarly, the impact of the revised densities and temperatures on the oxygen abundance, dex, is also within 1σ–2σ. The impact is even smaller for the nitrogen abundance, with dex being much smaller than the N/O uncertainty.\r\n\r\nRelative UV abundances are impacted by changes in both the nebular conditions and the relevant abundance emission-line ratio. However, the resulting abundance deviations are small and within the original uncertainties: dex, dex, and dex. Thus, we conclude that while considering the impacts of hidden broad component contributions to the measured UV fluxes is important, the potential biases do not affect the main results or conclusions of this work.\r\n\r\n5. A Short Window of Intense WR Nitrogen Enrichment\r\nWe have presented evidence for WN stars in RXCJ2248-ID3 in two forms: first, the rest-frame optical WR blue bump discussed in Section 3 and shown in Figure 2; and second, a qualitative comparison of the CNO abundances to patterns expected for WR stars in Section 4.3 and Figure 4. Below, we examine the plausibility and impact of these WN stars by comparing RXCJ2248-ID3 to expected trends for WR stars with metallicity (Section 5.1), testing whether stellar yields can reproduce the observed CNO abundance pattern (Section 5.2) and assessing whether RXCJ2248-ID3’s stellar population can produce its inferred mass of ionized N (Section 5.3). Together, these lines of investigation suggest that the enhanced N/O and suppressed C/O in RXCJ2248-ID3 represent a short-lived enrichment phase, unique to metal-poor, highly star-forming galaxies in the early Universe (Section 5.4).\r\n\r\n5.1. WN Stars: The Dominant WR Phase at Low Metallicity\r\nTo date, no individual resolved WR stars have been directly observed at metallicities as low as RXCJ2248-ID3 (Z ∼ 0.1Z⊙). This is due, in part, to the lack of sufficiently close (D ≲ 1 Mpc for the young, crowded clusters hosting WR stars), metal-poor, star-forming galaxies (see C. Kehrig et al. 2013 for the closest metal-poor WR galaxy), but a scarcity of WR stars in metal-poor environments is also expected because mass loss through stellar winds scales with metallicity. We show the trend of the number of WC/WN stars as a function of metallicity in Figure 5. The observed number of WC/WN stars in M31 (∼175% Z⊙), the Milky Way (MW; Z⊙), M33 (∼40%–110% Z⊙), the Large Magellanic Cloud (LMC; ∼40% Z⊙), and the Small Magellanic Cloud (SMC; ∼20% Z⊙) suggest that the number of the WN/WC number ratio increases with decreasing metallicity (e.g., G. Meynet & A. Maeder 2005; P. A. Crowther 2007; P. Massey et al. 2015; K. Neugent & P. Massey 2019). This is because weaker metal line-driven winds, rotation, or binary effects in metal-poor stars may be able to expose their nitrogen-rich layers and initiate the WN phase but be insufficient to strip the stellar He atmosphere and reveal the carbon-rich core to initiate the WC phase. Thus, if WR stars form at Z ∼ 10% Z⊙, they are expected to be overwhelmingly WN-type. Additionally, A. A. C. Sander et al. (2026) recently discovered a new class of WN–WO stars that point to a low-metallicity WR evolutionary channel in which stars pass directly from the WN to WO phase, potentially explaining spectra that show evidence for WN-like enrichment and hard ionizing radiation without clear WC signatures.\r\n\r\nZoom InZoom OutReset image size\r\nFigure 5. Observed and theoretical ratios of WC/WN star numbers as a function of metallicity. Observed values for the SMC, LMC, MW, and M31 were compiled by K. Neugent & P. Massey (2019), while newer values for M33 come from K. F. Neugent & P. Massey (2023). For comparison, we also plot the trend presented in P. Massey et al. (2017) for BPASS v2.0 binary stellar population synthesis burst models for 12+log(O/H) > 8 (solid line green line), which we extrapolate to lower metallicities (dashed line). Enrichment from WR stars was used to explain the CNO abundances in GN-z11 by C. Kobayashi & A. Ferrara (2024). We note the metallicity for GN-z11 determined by Z. Martinez et al. (2025) is consistent with a WC/WN ratio of ∼0.1–0.2 and the metallicity for RXCJ2248-ID3 from the current work, which predicts a much lower WC/WN ratio of ∼0.03–0.10. Therefore, very little carbon enrichment from WC stars is expected for RXCJ2248-ID3.\r\n\r\nDownload figure:\r\n\r\nStandard imageHigh-resolution image\r\nThe spectral features of RXCJ2248-ID3 support the picture of WN star feedback at low metallicity. As shown in Figure 2, the He ii emission is moderately broadened, the N iii λ4642 line in the blue bump is prominent, and there is no evidence for the red bump C iv feature, all consistent with the presence of WN stars at low metallicity. The weakness of the He ii emission in terms of both flux and velocity width is expected for the low-metallicity environment of RXCJ2248-ID3 (∼10% Z⊙) due to reduced wind velocities and mass-loss rates (e.g., A. A. C. Sander et al. 2020). Similarly weak WN features have also been reported in the nearby metal-poor galaxy SBS 0335-052 (Y. I. Izotov et al. 2006) and, at cosmic noon, the z ∼ 2.37 lensed galaxy the Sunburst Arc (T. E. Rivera-Thorsen et al. 2024) and the z ∼ 2.22 M4327 galaxy (M. Curti et al. 2025b).\r\n\r\nWe plot the WR blue bump profile of RXCJ2248-ID3 relative to the Sunburst Arc and M4327 in Figure 6. For ease of comparison, we convolve the Sunburst Arc R ∼ 2700 JWST/NIRSpec G140H spectrum to the R ∼ 1000 resolution of the RXCJ2248-ID3 spectrum. For M4327, we retrieved the G140M spectrum obtained as part of the Measuring Abundance at High Redshift with the Te Approach Survey (MARTA; E. Cataldi et al. 2025) from the Dawn JWST Archive (DJA; K. E. Heintz et al. 2024; A. de Graaff et al. 2025). Both the Sunburst Arc and M4327 spectra were scaled to similar He ii strengths as RXCJ2248-ID3. These spectra immediately reveal similar profiles, but with three distinct differences: (1) RXCJ2248-ID3 exhibits higher gas ionization, as evidenced by the strong [Ar iv] λλ4713,4741 emission; (2) the He ii stellar wind feature is significantly broader in both the Sunburst Arc (FWHM = 1370 km s−1) and M4327 (FWHM = 1460 km s−1) than RXCJ2248-ID3 (FWHM = 530 km s−1), consistent with stronger stellar winds at the higher metallicities of the Sunburst Arc: (or Z ∼ 0.7 Z⊙; Z. Martinez et al. 2025) and M4327: (or Z ∼ 0.3 Z⊙; M. Curti et al. 2025b); and (3) the WR N iii λ4642 line is much stronger in RXCJ2248-ID3, which lacks WR C iv λλ5803,5814 emission, while the Sunburst Arc and M4327 exhibit both N iii and C iv emission. These differences support a scenario in which the z ∼ 2 WR galaxies hosts both WC and WN stars, but the more metal-poor RXCJ2248-ID3 hosts a young population of WN stars with no or very little WC contribution.\r\n\r\nZoom InZoom OutReset image size\r\nFigure 6. The blue WR region of the optical spectrum of RXCJ2248-ID3 (purple) is shown in comparison to the z ∼ 2.37 Sunburst Arc spectrum from T. E. Rivera-Thorsen et al. (2024, blue), which has been convolved to R ∼ 1000 to match RXCJ2248-ID3, and the z = 2.22 M4327 spectrum obtained from the DJA, but originally presented in M. Curti et al. (2025b, turquoise). All three galaxies show characteristic signs of hosting WN stars but RXCJ2248-ID3 shows striking N iii λ4642 emission that is much stronger than both the Sunburst Arc and M4327. On the other hand, the Sunburst Arc and M4327 show broader He ii emission, which is expected for more metal-rich galaxies as stellar winds scale with metallicity.\r\n\r\nDownload figure:\r\n\r\nStandard imageHigh-resolution image\r\n5.2. Relative Chemical Enrichment from WN Stars\r\nWith the highest redshift detection of WN stars to date, we now explore their chemical yields as a source of the abundance pattern in RXCJ2248-ID3. C. Charbonnel et al. (2023) performed a comparable analysis for the extreme N/O ratio observed in GN-z11 and found that such rapid nitrogen enrichment could arise from normal massive stars with M⋆ ∼ 20–120 M⊙ or from supermassive stars (M⋆ ≳ 1000 M⊙) in protoglobular cluster environments. Their results and those of R. Marques-Chaves et al. (2024) further demonstrated that the short-lived WN-like phase can produce large N/O ratios within a few megayears of the burst, consistent with the timescales inferred here, but that the observed C/O ratios are only compatible over a very short time interval. Building on this theoretical groundwork, C. Kobayashi & A. Ferrara (2024) showed that a dual-burst chemical evolution model with a short WR-dominated enrichment phase could also match GN-z11’s enrichment pattern. Similarly, R. Marques-Chaves et al. (2024) used N yields from rotating massive stars to demonstrate that a young, WR-dominated stellar population could reproduce the observed CNO enrichment pattern in CEERS-1019.\r\n\r\nThe models above provide a valuable physical framework for linking stellar yields to galaxy-scale abundance evolution at early times. To extend the methodologies outlined by these works to RXCJ2248-ID3, we first examine the dual-burst chemical evolution model of C. Kobayashi & A. Ferrara (2024), which was fine-tuned to reproduce the enhanced N/O in GN-z11 (reported by R. Maiolino et al. 2024). This model invokes two bursts of star formation, where the second triggers a narrow (≲1 Myr) phase of WR-dominated enrichment. While the model can easily reach the N/O enrichment level of RXCJ2248-ID3, it was also designed to yield the higher O/H and C/O abundances observed in GN-z11 than in RXCJ2248-ID3, which was achieved, in part, by enrichment from WC stars. The updated O/H abundance for GN-z11 determined by Z. Martinez et al. (2025) makes it consistent with some carbon enrichment from WC stars, as shown in Figure 5. However, with a metallicity of only Z ∼ 0.10 Z⊙, the WR population in RXCJ2248-ID3 is expected to consist of few WC stars, and so an updated chemical evolution model is needed to match its unique CNO abundance pattern.\r\n\r\nWe modify the C. Kobayashi & A. Ferrara (2024) dual-burst model to be more appropriate for the metal-poor conditions in RXCJ2248-ID3. In particular, the galactic chemical evolution (GCE) model uses the same star formation history and the standard IMF (for 0.01–120 M⊙) as in the fiducial model in C. Kobayashi & A. Ferrara (2024) but reduces the contribution from WC stars. C/O ratios of the nucleosynthesis yields vary depending on the uncertain nuclear reaction rates (e.g., 12C(α, γ)16O) and the treatment of convection and mass loss (C. Kobayashi et al. 2006). In the updated model, 12C and 16O yields are taken from C. Kobayashi et al. (2020) for all mass ranges of stars but the contributions from the WC wind phase is scaled to ∼15% in order to match the empirical trends and theoretical expectations that most massive stars will have insufficient winds to remove their He envelopes at such low metallicities.\r\n\r\nWe plot the updated metal-poor dual-burst model in the bottom row of Figure 4 as a time-series of points that are color coded by the age since the onset of the second burst. In this model, the observed N/O, O/H, and C/O abundances of RXCJ2248-ID3 are reached simultaneously ∼4.2 Myr after the onset of the second burst. This young age is consistent with enrichment from WN stars and with the derived clump age of Myr (A. Claeyssens 2025). Thus, the N/O-enhanced and relatively C/O-deficient conditions in RXCJ2248-ID3 are produced by a short-lived evolutionary phase following intense, bursty star formation.\r\n\r\nWe note that the duration and impact of the WN phase may be significantly extended if the stars evolve in binary systems. In the M. Limongi & A. Chieffi (2018) single-star models, the WN phase typically lasts ∼0.03–0.3 Myr and, due to the metallicity-dependent winds, require high initial masses (∼40 M⊙) to expose the He- and N-rich layers. However, in close binaries, envelope stripping via mass transfer or common-envelope evolution can induce WR phases in lower-mass stars (20–30 M⊙), largely independent of the stellar metallicity. This channel can significantly prolong the WN lifetime (up to ∼1 Myr) depending on the binary mass ratio and separation (e.g., J. J. Eldridge et al. 2017; Y. Götberg et al. 2019; D. R. Aguilera-Dena et al. 2022). As a result, binary evolution may enhance both the frequency and duration of the chemically selective N/O enrichment phase, such as that observed in RXCJ2248-ID. On the other hand, L. Boco et al. (2025) successfully modeled observations of single WR stars in the SMC, suggesting that binary stripping may not be required to produce WR stars at low metallicity. Clearly, the frequency, lifetimes, and formation channels of WR stars in low-metallicity environments are not yet well understood. Future work incorporating current binary and single star WR pathways into chemical evolution models may, therefore, be essential for capturing the full range of nitrogen feedback in low-metallicity starbursts at high redshift.\r\n\r\nTaken together, the massive star enrichment scenario presented here, and explored in C. Charbonnel et al. (2023), R. Marques-Chaves et al. (2024), and C. Kobayashi & A. Ferrara (2024), demonstrates that selective enrichment of nitrogen by WN-dominated feedback can naturally reproduce the observed CNO abundance pattern in compact, low-metallicity starbursts such as RXCJ2248-ID3. We can now paint a full picture of the ISM in RXCJ2248-ID3. The consistency of N/O across ions spanning a wide range of ionization potentials suggests that the WN-enriched material has been efficiently mixed throughout the ionized gas. This apparent chemical homogeneity does not contradict the strong density and temperature stratification inferred from our diagnostics: a clumpy or multiphase ISM can remain compositionally uniform if the enriched ejecta are well dispersed. Given the extreme compactness of RXCJ2248-ID3 (Re ≈ 20 pc), the characteristic dynamical and sound-crossing times are only a few ×105 yr, comparable to or shorter than the duration of the WN phase itself. Under such conditions, turbulent and radiative mixing can rapidly homogenize the heavy-element yields, producing a chemically uniform yet physically structured nebula.\r\n\r\n5.3. The N Mass Budget\r\nA crucial point of validation is whether an intense burst of star formation so early in the Universe could have produced the amount of N present in RXCJ2248-ID3. Similar to the analysis in R. Marques-Chaves et al. (2024), we test this by first estimating the ionized nitrogen mass using\r\n\r\nwhere the atomic mass ratio is mN/mH = 14 and N/H is the nitrogen abundance of the ionized gas. The hydrogen gas mass MH is derived from the Hα luminosity as\r\n\r\nwhere mH = 1.67 × 10−27 kg, h = 6.626 × 10−27 erg s−1, νHα is the frequency of the Hα emission line, and cm3 s−1 is the Case B effective recombination coefficient for Hα assuming a Te = 1.97 × 104 K. We estimate the Hα luminosity using a luminosity distance of dL(z = 6.1025) =1.817 × 1029 cm, the collision-corrected narrow-component Hα flux, and a magnification of μ = 6.8877 (L. Furtak et al. 2025) to be LHα =  1.20 × 1042 erg s−1. Combining this LHα with the equivalent width (EW)(Hα) = 1457 Å, we derive the star formation rate (SFR) using the simulation-based SFR(Hα) calibration from I. G. Kramarenko et al. (2026). This method was developed to be more appropriate for the bursty conditions at high redshift than traditional calibrations and gives SFR = 3.2 M⊙ yr−1, similar to the SED-derived SFRs assuming a constant SFH for 1 Myr () and 10 Myr (; see Table 1). Adopting a filling factor of ε = 0.01-0.10, assuming a compact starburst (e.g., R. C. Kennicutt 1984; G. Stasińska & D. Schaerer 1997), a density of 104 cm−3, and the measured N/H value, we calculate the ionized nitrogen mass to be .\r\n\r\nWe then compute the total nitrogen mass that can be produced by the recent burst of star formation using the integrated nitrogen yield produced by the modified C. Kobayashi & A. Ferrara (2024) model for the SED-derived stellar mass of assuming a continuous SFH over the duration of the second burst (∼4.2 Myr). This results in a total N mass of 435 M⊙, implying that ∼% of the gas is retained from the WN winds and ionized when matched to the expected ionized N mass (∼) from the crudely calculated observed value. Thus, WN stars formed in a recent burst within a compact, high-density, and very clumpy/inhomogeneous (low-filling-factor) environment can plausibly explain the N mass in RXCJ2248-ID3, even at low metallicity (∼10% Z⊙), without invoking a top-heavy IMF or exotic enrichment channels.\r\n\r\n5.4. The Ephemeral Imprint of WN Star on High−z Galaxies\r\nThe prominence of N/O enhancement at z ≳ 5 but relative rarity in local star-forming galaxies likely reflects a combination of environmental conditions and evolutionary factors that are unique to the early Universe. To examine the likely environments, we plot the SFR surface density (ΣSFR) versus EW of Hβ in Figure 7 for both z ≳ 6 N emitters (RXCJ2248-ID3: M. W. Topping et al. 2024, this work; GNz9p4: D. Schaerer et al. 2024; GN-z11, EW(Hβ) inferred from Hγ: A. J. Bunker et al. 2023; S. Tacchella et al. 2023; GDS 3073: E. Vanzella et al. 2010; H. Übler et al. 2023; X. Ji et al. 2024; CEERS-1019: R. L. Larson et al. 2023; R. Marques-Chaves et al. 2024; A1703-zd6: M. W. Topping et al. 2025b) and local star-forming galaxies with enhanced SFRs from the COS Legacy Archive Spectroscopic SurveY (CLASSY; B. L. James et al. 2021; D. A. Berg et al. 2022; N/O from K. Z. Arellano-Córdova et al. 2025). The high-redshift galaxies, such as RXCJ2248-ID3, exhibit compact morphologies (Re ≲ 102 pc) that lead to much higher SFR surface densities than seen at z ∼ 0, as well as bursty star formation histories that favor the rapid buildup of massive stars capable of entering the short-lived WN phases (M⋆ > 20 M⊙). The high-redshift N emitters also have high Hβ EWs (>200 Å) that are indicative of young current bursts of star formation (<5 Myr). This suggests that compactness alone is not enough to observe enhanced N/O; we must also observe these galaxies at the fleeting moments of very young bursts when WR stars are most active.\r\n\r\nZoom InZoom OutReset image size\r\nFigure 7. SFR surface density versus Hβ EW for high-redshift (z > 5) N emitters versus z ∼ 0 galaxies from the CLASSY survey (SFR: D. A. Berg et al. 2022; N/O: K. Z. Arellano-Córdova et al. 2025), which have enhanced SFRs similar to z ∼ 2–3 galaxies. High-redshift N emitters are only observed at young ages (≲5 Myr), as indicated by the high Hβ EWs (EW> 200 Å), and in compact, dense environments (ΣSFR > 10 M⊙ yr−1 kpc−1). Note that RXCJ2248-ID3 is plotted here using the properties derived from M. W. Topping et al. (2024) for continuous star formation to be consistent with the other N-emitter measurements.\r\n\r\nDownload figure:\r\n\r\nStandard imageHigh-resolution image\r\nFigure 7 suggests a scenario of elevated N/O at low metallicity being preferentially seen in galaxies with high SFR surface densities and young stellar ages (e.g., D. Schaerer et al. 2024; M. W. Topping et al. 2024; Z. Martinez et al. 2025). R. Marques-Chaves et al. (2024) also suggest that the elevated N/O and high-ionization spectrum of CEERS-1019 trace a short evolutionary window of a ≲5 Myr burst dominated by WN-like feedback. Furthermore, the theoretical models of C. Charbonnel et al. (2023) predict that such phases are characteristic of young, dense stellar systems, potentially analogous to protoglobular clusters, reinforcing that our observed WN-driven enrichment is a natural outcome of clustered, bursty star formation at early times.\r\n\r\nAt low metallicity, weaker stellar winds require higher initial masses for stars to reach the WR phase, so a larger total stellar mass must form in a burst to produce a detectable population of WN stars. In compact galaxies beyond cosmic noon, this condition is naturally met in systems with high SFR surface densities, which statistically sample the upper IMF more fully and produce a detectable population of WN stars (e.g., J. Brinchmann et al. 2008; M. Shirazi & J. Brinchmann 2012). Furthermore, the WR enrichment signature is short-lived: it must be captured during the brief WN-dominated phase (tburst ≲ 5 Myr and ΔtWN ≲ 0.3 Myr), before dilution from WC stars, CCSNe, or delayed AGB enrichment. These timing constraints imply that only a small fraction of the star-forming galaxies in the distant Universe will be caught in this phase. The detection of WR-driven N/O enhancement at high redshift thus reflects a brief evolutionary stage where intense, rapid feedback from a large number of WN stars briefly imprints nonuniform elemental enrichment patterns (i.e., elevated N/O), which are expected to be quickly washed away. As soon as the system evolves beyond the WN phase, subsequent WC or CCSN yields will rapidly dilute the N excess and alter the overall abundance patter (e.g., increasing C/O, lowering N/C).\r\n\r\nRecently, M. W. Topping et al. (2025b) showed that galaxies with significant N iv] emission (corresponding to extreme N/O enhancement), are found exclusively among galaxies with extreme [O iii]+Hβ EWs of 2600–4200 Å. Galaxies with such high [O iii]+Hβ EWs are in the upper 2% tail of the EW distribution at z ≳ 4 and are outliers at z ∼ 0. This strongly suggests that high N/O outliers are confined to the youngest stellar populations undergoing their most intense bursts of star formation in the early Universe (e.g., R. Endsley et al. 2023, 2025; J. Matthee et al. 2023; M. W. Topping et al. 2025b).\r\n\r\nIn this context, M. W. Topping et al. (2025b) found that 30% of galaxies with EW[O III] + Hβ > 2000 Å show strong nitrogen emission, corresponding to ∼0.6% of their UV-selected parent population. If this 0.6% population corresponds to enhanced N/O during the ΔtWN ∼ 0.3 Myr WN phase, it would imply a characteristic burst timescale of ∼50 Myr. A practical consequence is that young bursts substantially increase the light-to-mass ratios and, thus, the likelihood of detection in flux-limited samples (e.g., C. A. Mason et al. 2023; J. B. Muñoz et al. 2023; G. Sun et al. 2023). Therefore, the observed frequency of strong nitrogen emitters at fixed MUV is likely biased high relative to their intrinsic abundance (e.g., at fixed stellar mass). Given the detectability bias toward burst phases, this tburst may represent a lower limit, with the true interval plausibly longer. This timescale is supported by recent analyses of the scatter in the star-forming main sequence and time-resolved SFR indicators at z ∼ 3–9 that suggest burst cycles of tens-of-megayear timescales (albeit with broad distributions, e.g., C. Simmonds et al. 2025). Thus, the combination of extreme-EW selection and N iv] frequency provides a novel timing argument that WN-driven enrichment is tightly coupled to very young, transient starburst phases beyond cosmic noon.\r\n\r\nTaken together, the arguments presented in this work suggest that nitrogen outliers are not exotic exceptions, but rather a brief, WN-enriched phase that any high-redshift galaxy with sufficiently high SFR surface density can pass through. In contrast, numerous low-redshift WR galaxies exhibit young populations that include WN and WC stars but show little or no N/O enhancement (e.g., Y. I. Izotov et al. 2006; C. Kehrig et al. 2013). This difference underscores that similar stellar populations do not guarantee the same chemical signatures; instead, the extreme densities, compactness, and rapid mixing timescales of high-redshift starbursts likely make WN-driven enrichment both more pronounced and more transient. In this view, N/O outliers in the early Universe are not anomalies, but rather are the chemical fingerprints of galaxies caught midburst, showing fleeting yet inevitable markers of early galaxy evolution.\r\n\r\n6. Conclusions\r\nWe have presented a detailed enrichment scenario by WN stars that explains the extreme nitrogen enrichment in the metal-poor (∼10% Z⊙), high surface-density (1.34 × 103 M⊙ pc−2), high-redshift (z = 6.1025), lensed galaxy RXCJ2248-ID3. These measurements were made possible by exceptionally deep JWST/NIRSpec medium-resolution spectroscopy of RXCJ2248-ID3, obtained as part of the GLIMPSE-D survey. The unprecedented depth and S/N of the GLIMPSE-D spectrum allow spectral measurements typically limited to the nearby Universe, including consistent broad components in the Balmer series and [O iii] λ4364 and λλ4960,5008 lines, faint [Ar iv] λλ4713,4741 emission, and signatures of WR stars. Specifically, we detected the emission characteristic of WN-type stars, including strong N iii λ4642 and broadened He ii λ1640 and λ4687 emission, marking RXCJ2248-ID3 as the most distant galaxy to date with spectroscopic detections of WR stars.\r\n\r\nWe performed a detailed nebular analysis, self-consistently measuring the reddening, high-ionization temperature (Te(O+2)), and densities from five different diagnostics across a wide ionization range. We measure a low reddening value of from the Hγ/Hβ ratio but find an excess in the Hα/Hβ ratio of 0.204 due to collisional excitation of Hα. The measured densities span the range of 1.15 × 103 cm−3 ≤ ne ≤ 2.65 × 105 cm−3 and show strong evidence for nebular density stratification, with systematically higher densities in the highest-ionization gas and UV emission tracing gas at higher densities than those traced by optical diagnostics. This structure implies a highly clumpy, multiphase ISM. We note that such high-density, multiphase gas leads to densities from optical diagnostics that are biased to the low end of the density range due to their low critical densities. Therefore, we recommend using UV density diagnostics because they are more robust in high-density environments: ne(Si+2), ne(C+2), and ne(N+3) trace the densities in the low-, intermediate-, and high-ionization gas, respectively. As a result, we measure a direct-method metallicity of .\r\n\r\nUsing the full rest-UV+optical spectra, we present the first robust, consistent measurements of N/O abundance in any galaxy using three ionization stages of nitrogen (N+/O+, N+2/O+2, N+3/O+2). The uniformity of our N/O measurements suggests that the N/O enrichment is spatially extended and well mixed throughout the ionized ISM. Empirical trends suggest C/O should follow a similar trend as N/O, and thus also be enhanced. In contrast, we find C/O to be significantly depleted relative to N/O, suggesting nonuniform elemental enrichment likely driven by WN stars with little to no contribution from WC stars.\r\n\r\nThe CNO abundance pattern is best reproduced by a modified version of the dual-burst chemical evolution model from C. Kobayashi & A. Ferrara (2024) that reduces the contribution from WC stars relative to WN stars, as expected in metal-poor environments. The resulting short-lived WN phase ejects N-rich, C-poor material. We use this chemical evolution model to assess whether the observed N mass can plausibly arise from the recent star formation in RXCJ2248-ID3 and estimate an ionized N mass of 435 M⊙. This value is consistent with the N mass estimated from the observed emission lines of M⊙ if % of the N gas is ionized.\r\n\r\nThese results demonstrate that standard stellar evolution models can reproduce both the CNO pattern and the total nitrogen mass observed without invoking an exotic IMF or enrichment channel. The uniform N/O ratios across multiple ionization zones further suggest that the WN yields were rapidly mixed into a relatively pristine ambient ISM, preserving the global enhancement observed in RXCJ2248-ID3. Although RXCJ2248-ID3 exhibits strong density and temperature stratification, this structural complexity does not necessarily imply chemical inhomogeneity. The consistent N/O ratios across ions tracing vastly different physical conditions indicate that the enriched material was efficiently dispersed throughout the multiphase ISM. In such a compact (Re ≈ 20 pc), high-pressure environment, turbulent and radiative mixing can homogenize the chemical composition on timescales comparable to, or shorter than, the brief WN phase itself, yielding a chemically uniform yet physically clumpy nebula.\r\n\r\nImportantly, the abundance pattern and physical conditions observed in RXCJ2248-ID3 can only be explained if the galaxy is caught during a narrow evolutionary window within a few megayears of a massive, compact starburst when WN stars dominate chemical feedback. At low metallicity, stars require higher initial masses to reach the WR phase, making such enrichment episodes rare and dependent on sufficiently high SFRs to fully populate the upper IMF. Furthermore, the WN phase itself is extremely short-lived (∼0.03–0.3 Myr) and easily masked by subsequent WC winds, CCSNe, or AGB stars contributions. These timing and SFR constraints make WR-driven N/O enhancement a rare phenomenon associated with extreme starburst conditions that are more common in the early Universe, and which are scarce in the local Universe.\r\n\r\nOur results suggest that the WN-driven N/O enrichment we observe is not a peculiar property of a single system, but rather a brief phase that essentially all high-redshift galaxies (z > 5) with sufficiently high SFR surface densities to produce significant numbers of WN stars likely undergo. In particular, the work of M. W. Topping et al. (2025b) can be used to link N/O outliers to the most extreme [O iii]+Hβ EWs. The observed frequency of such EWs combined with the short lifetime of the WN phase implies a burst cycle of order ∼50 Myr, consistent with galaxies repeatedly cycling through short, bursty episodes of enrichment. Thus, the GLIMPSE-D spectrum of RXCJ2248-ID3 provides not only the first direct evidence of WN stars shaping the chemical evolution of z > 5 galaxies but also a timing argument that situates N/O outliers as a natural, fleeting, phase of high-redshift star formation.\r\n\r\nTaken together, our findings are a glimpse into a short-lived phase of chemically selective enrichment from WN stars at cosmic dawn, providing a physically self-consistent solution to the extreme N/O enhancement and relative C/O depletion observed in RXCJ2248-ID3 and galaxies like it. Thus, RXCJ2248-ID3 serves as a benchmark case for interpreting chemically enriched, stratified, multiphase starbursts in the early Universe.\r\n\r\nAcknowledgments\r\nWe thank the referee for their thorough review of our calculations and analysis and for their helpful suggestions, which greatly improved the robustness of our results and the clarity of the text. This work is based on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These observations are associated with program #9223. This work has received funding from the Swiss State Secretariat for Education, Research and Innovation (SERI) under contract No. MB22.00072, as well as from the Swiss National Science Foundation (SNSF) through project grant 200020_207349. The Cosmic Dawn Center (DAWN) is funded by the Danish National Research Foundation under grant DNRF140. The Dunlap Institute is funded through an endowment established by the David Dunlap family and the University of Toronto. We acknowledge the support of the Canadian Space Agency (CSA) [25JWGO4A06]. HA acknowledges support from CNES, focused on the JWST mission, and the Programme National Cosmology and Galaxies (PNCG) of CNRS/INSU with INP and IN2P3, co-funded by CEA and CNES and support by the French National Research Agency (ANR) under grant ANR-21-CE31-0838. The JWST data presented in this article from program #9223 were obtained from the Mikulski Archive for Space Telescopes (MAST) at the Space Telescope Science Institute. The specific observations analyzed can be accessed via DOI: 10.17909/8642-1k68.","article_number":"112","volume":1003,"publication_status":"published","oa_version":"Published Version","tmp":{"name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","image":"/images/cc_by.png","short":"CC BY (4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode"},"publisher":"IOP Publishing","scopus_import":"1","fulldoi":"https://doi.org/10.3847/1538-4357/ae5e4c","DOAJ_listed":"1","type":"journal_article"},{"citation":{"short":"W.Q. Sun, R.P. Naidu, J.J. Matthee, A. De Graaff, J. Chisholm, J.E. Greene, P.A. Oesch, A. Torralba Torregrosa, R.E. Hviding, G. Brammer, R.A. Simcoe, S. Bose, R. Bouwens, P. Dayal, A.C. Eilers, Q. Fei, L.J. Furtak, R. Gottumukkala, A. Goulding, K.E. Heintz, M. Hirschmann, V. Kokorev, J. Leja, Z. Liu, P. Natarajan, A.D. Santarelli, D.J. Setton, A. Smith, S. Tacchella, M. Volonteri, F. Walter, A. Weibel, C.C. Williams, The Open Journal of Astrophysics 9 (2026).","apa":"Sun, W. Q., Naidu, R. P., Matthee, J. J., De Graaff, A., Chisholm, J., Greene, J. E., … Williams, C. C. (2026). Little Red Dot - Host Galaxy = Black Hole Star: A gas-enshrouded heart at the center of every Little Red Dot. <i>The Open Journal of Astrophysics</i>. Maynooth Academic Publishing. <a href=\"https://doi.org/10.33232/001c.162505\">https://doi.org/10.33232/001c.162505</a>","ama":"Sun WQ, Naidu RP, Matthee JJ, et al. Little Red Dot - Host Galaxy = Black Hole Star: A gas-enshrouded heart at the center of every Little Red Dot. <i>The Open Journal of Astrophysics</i>. 2026;9. doi:<a href=\"https://doi.org/10.33232/001c.162505\">10.33232/001c.162505</a>","mla":"Sun, Wendy Q., et al. “Little Red Dot - Host Galaxy = Black Hole Star: A Gas-Enshrouded Heart at the Center of Every Little Red Dot.” <i>The Open Journal of Astrophysics</i>, vol. 9, Maynooth Academic Publishing, 2026, doi:<a href=\"https://doi.org/10.33232/001c.162505\">10.33232/001c.162505</a>.","ieee":"W. Q. Sun <i>et al.</i>, “Little Red Dot - Host Galaxy = Black Hole Star: A gas-enshrouded heart at the center of every Little Red Dot,” <i>The Open Journal of Astrophysics</i>, vol. 9. Maynooth Academic Publishing, 2026.","chicago":"Sun, Wendy Q., Rohan P. Naidu, Jorryt J Matthee, Anna De Graaff, John Chisholm, Jenny E. Greene, Pascal A. Oesch, et al. “Little Red Dot - Host Galaxy = Black Hole Star: A Gas-Enshrouded Heart at the Center of Every Little Red Dot.” <i>The Open Journal of Astrophysics</i>. Maynooth Academic Publishing, 2026. <a href=\"https://doi.org/10.33232/001c.162505\">https://doi.org/10.33232/001c.162505</a>.","ista":"Sun WQ, Naidu RP, Matthee JJ, De Graaff A, Chisholm J, Greene JE, Oesch PA, Torralba Torregrosa A, Hviding RE, Brammer G, Simcoe RA, Bose S, Bouwens R, Dayal P, Eilers AC, Fei Q, Furtak LJ, Gottumukkala R, Goulding A, Heintz KE, Hirschmann M, Kokorev V, Leja J, Liu Z, Natarajan P, Santarelli AD, Setton DJ, Smith A, Tacchella S, Volonteri M, Walter F, Weibel A, Williams CC. 2026. Little Red Dot - Host Galaxy = Black Hole Star: A gas-enshrouded heart at the center of every Little Red Dot. The Open Journal of Astrophysics. 9."},"date_created":"2026-06-07T22:01:36Z","OA_type":"diamond","year":"2026","department":[{"_id":"JoMa"}],"status":"public","oa":1,"has_accepted_license":"1","author":[{"first_name":"Wendy Q.","last_name":"Sun","full_name":"Sun, Wendy Q."},{"last_name":"Naidu","first_name":"Rohan P.","full_name":"Naidu, Rohan P."},{"last_name":"Matthee","id":"7439a258-f3c0-11ec-9501-9df22fe06720","first_name":"Jorryt J","orcid":"0000-0003-2871-127X","full_name":"Matthee, Jorryt J"},{"full_name":"De Graaff, Anna","last_name":"De Graaff","first_name":"Anna"},{"full_name":"Chisholm, John","last_name":"Chisholm","first_name":"John"},{"first_name":"Jenny E.","last_name":"Greene","full_name":"Greene, Jenny E."},{"last_name":"Oesch","first_name":"Pascal A.","full_name":"Oesch, Pascal A."},{"last_name":"Torralba Torregrosa","id":"018f0249-0e87-11f0-b167-cbce08fbd541","first_name":"Alberto","full_name":"Torralba Torregrosa, Alberto","orcid":"0000-0001-5586-6950"},{"first_name":"Raphael E.","last_name":"Hviding","full_name":"Hviding, Raphael E."},{"first_name":"Gabriel","last_name":"Brammer","full_name":"Brammer, Gabriel"},{"full_name":"Simcoe, Robert A.","first_name":"Robert A.","last_name":"Simcoe"},{"full_name":"Bose, Sownak","last_name":"Bose","first_name":"Sownak"},{"full_name":"Bouwens, Rychard","last_name":"Bouwens","first_name":"Rychard"},{"full_name":"Dayal, Pratika","first_name":"Pratika","last_name":"Dayal"},{"first_name":"Anna Christina","last_name":"Eilers","full_name":"Eilers, Anna Christina"},{"last_name":"Fei","first_name":"Qinyue","full_name":"Fei, Qinyue"},{"first_name":"Lukas J.","last_name":"Furtak","full_name":"Furtak, Lukas J."},{"first_name":"Rashmi","last_name":"Gottumukkala","full_name":"Gottumukkala, Rashmi"},{"full_name":"Goulding, Andy","last_name":"Goulding","first_name":"Andy"},{"full_name":"Heintz, Kasper E.","first_name":"Kasper E.","last_name":"Heintz"},{"full_name":"Hirschmann, Michaela","first_name":"Michaela","last_name":"Hirschmann"},{"first_name":"Vasily","last_name":"Kokorev","full_name":"Kokorev, Vasily"},{"full_name":"Leja, Joel","last_name":"Leja","first_name":"Joel"},{"full_name":"Liu, Zhaoran","first_name":"Zhaoran","last_name":"Liu"},{"full_name":"Natarajan, Priyamvada","last_name":"Natarajan","first_name":"Priyamvada"},{"full_name":"Santarelli, Andrew D.","first_name":"Andrew D.","last_name":"Santarelli"},{"last_name":"Setton","first_name":"David J.","full_name":"Setton, David J."},{"first_name":"Aaron","last_name":"Smith","full_name":"Smith, Aaron"},{"full_name":"Tacchella, Sandro","first_name":"Sandro","last_name":"Tacchella"},{"first_name":"Marta","last_name":"Volonteri","full_name":"Volonteri, Marta"},{"full_name":"Walter, Fabian","first_name":"Fabian","last_name":"Walter"},{"full_name":"Weibel, Andrea","first_name":"Andrea","last_name":"Weibel"},{"first_name":"Christina C.","last_name":"Williams","full_name":"Williams, Christina C."}],"external_id":{"arxiv":["2601.20929"]},"month":"05","date_published":"2026-05-25T00:00:00Z","date_updated":"2026-06-08T08:25:40Z","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","ddc":["520"],"OA_place":"publisher","file_date_updated":"2026-06-08T08:23:37Z","intvolume":"         9","publication_identifier":{"eissn":["2565-6120"]},"language":[{"iso":"eng"}],"_id":"21951","day":"25","PlanS_conform":"1","title":"Little Red Dot - Host Galaxy = Black Hole Star: A gas-enshrouded heart at the center of every Little Red Dot","arxiv":1,"doi":"10.33232/001c.162505","acknowledgement":"We thank the two anonymous referees for their insightful comments that have strengthened this work.\r\nWQS and RPN acknowledge funding from JWST programs GO-3516, GO-5224, and the MIT Undergraduate\r\nResearch Opportunities Program (UROP). Support for\r\nthis work was provided by NASA through the NASA\r\nHubble Fellowship grant HST-HF2-51515.001-A awarded\r\nby the Space Telescope Science Institute, which is operated by the Association of Universities for Research in\r\nAstronomy, Incorporated, under NASA contract NAS5-\r\n26555. RPN thanks Neil Pappalardo and Jane Pappalardo for their generous support of the MIT Pappalardo Fellowships in Physics, and for their enthusiasm\r\nand encouragement for pursuing the earliest galaxies and\r\nblack holes. JM and AT acknowledge funding from the\r\nEuropean Union (ERC, AGENTS, 101076224). KEH\r\nacknowledges support from the Independent Research Fund Denmark (DFF) under grant 5251-00009B and cofunding by the European Union (ERC, HEAVYMETAL,\r\n101071865). Views and opinions expressed are, however,\r\nthose of the authors only and do not necessarily reflect\r\nthose of the European Union or the European Research\r\nCouncil. Neither the European Union nor the granting\r\nauthority can be held responsible for them. REH acknowledges support by the German Aerospace Center\r\n(DLR) and the Federal Ministry for Economic Affairs\r\nand Energy (BMWi) through program 50OR2403 ‘RUBIES’.\r\nThe data products presented herein were retrieved\r\nfrom the Dawn JWST Archive (DJA). DJA is an initiative of the Cosmic Dawn Center (DAWN), which is\r\nfunded by the Danish National Research Foundation under grant DNRF140. This work is based on observations\r\nmade with the NASA/ESA/CSA James Webb Space\r\nTelescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope\r\nScience Institute, which is operated by the Association\r\nof Universities for Research in Astronomy, Inc., under\r\nNASA contract NAS 5-03127 for JWST. Support for\r\nprograms #3516, #5224, #5664 was provided by NASA\r\nthrough grants from the Space Telescope Science Institute, which is operated by the Association of Universities\r\nfor Research in Astronomy, Inc., under NASA contract\r\nNAS 5-03127.\r\nThe spectra used in this paper are associated with programs 1180 (D’Eugenio et al. 2025d), 1181 (PI: D. Eisenstein), 1208 (Willott et al. 2022), 1210 (PI: N. Luetzgendorf), 1211 (Maseda et al. 2024), 1212 - 1215 (PI: N.\r\nLuetzgendorf), 1228 (Luhman et al. 2024b), 1229 (Luhman et al. 2024a), 1286 (PI: N. Luetzgendorf), 1287 (PI:\r\nK. Isaak), 1345 (Finkelstein et al. 2023), 1433 (Hsiao\r\net al. 2024), 1747 (PI: G. Roberts-Borsani), 2028 (Wang\r\net al. 2024c), 2073 (PI: J. Hennawi), 2198 (Barrufet\r\net al. 2025), 2282 (Bradley et al. 2023), 2561 (Bezanson\r\net al. 2024), 2565 (Nanayakkara et al. 2025), 2640 (PI:\r\nW. Best), 2750 (Arrabal Haro et al. 2023), 2756 (Mascia et al. 2024), 2767 (Williams et al. 2023b), 2770 (PI:\r\nM. McCaughrean), 3073 (Castellano et al. 2024), 3215\r\n(Eisenstein et al. 2025), 4106 (PI: E. Nelson), 4233 (de\r\nGraaff et al. 2025c), 4446 (Frye et al. 2024), 4557 (PI: H.\r\nYan), 5105 (Shen et al. 2024), 5224 (PIs: P.A. Oesch &\r\nR.P. Naidu), 6368 (PI: M. Dickinson), 6541 (DeCoursey\r\net al. 2025), 6585 (PI: D. Coulter), 6642 (PI: J. Muzerolle\r\nPage), and FRESCO IFU (Matthee et al. 2024; Torralba\r\net al. 2025b).\r\nSoftware used in developing this work includes:\r\nmatplotlib (Hunter 2007), jupyter (Kluyver et al.\r\n2016), IPython (P´erez & Granger 2007), numpy\r\n(Oliphant 2015), scipy (Virtanen et al. 2020), TOPCAT\r\n(Taylor 2005), Astropy (Astropy Collaboration et al.\r\n2013), msaexp (Brammer 2023).","file":[{"content_type":"application/pdf","access_level":"open_access","date_created":"2026-06-08T08:23:37Z","date_updated":"2026-06-08T08:23:37Z","relation":"main_file","checksum":"33c4a444f7c37b3f47ecbd53eb187c1b","creator":"dernst","file_name":"2026_OpenJourAstrophysics_Sun.pdf","file_size":7591188,"file_id":"21952","success":1}],"publication":"The Open Journal of Astrophysics","project":[{"_id":"bd9b2118-d553-11ed-ba76-db24564edfea","name":"Young galaxies as tracers and agents of cosmic reionization","grant_number":"101076224"}],"abstract":[{"lang":"eng","text":"The central engines of Little Red Dots (LRDs) may be “black hole stars” (BH*s), early stages of\r\nblack hole growth characterized by dense gas envelopes. So far, the most direct evidence for BH*s\r\ncomes from a handful of sources where the host galaxy is completely outshone as suggested by their\r\nremarkably steep Balmer breaks. Here we present a novel scheme to disentangle BH*s from their\r\nhost galaxies assuming that the [O III]5008˚A line arises exclusively from the host. Using a sample\r\nof 98 LRDs (z ≈ 2 − 9) with high quality NIRSpec/PRISM spectra, we demonstrate that the hostsubtracted median stack displays a Balmer break > 2× stronger than massive quiescent galaxies,\r\nwith the rest-optical continuum resembling a blackbody-like SED (Teff ≈ 4050 K, log(Lbol) ≈ 43.9\r\nerg s−1\r\n, Reff ≈ 1300 au). We measure a steep Balmer decrement (Hα/Hβ > 10) and numerous\r\ndensity-sensitive features (e.g., Fe II, He I, O I). These are hallmark signatures of dense gas envelopes,\r\nproviding population-level evidence that BH*s indeed power LRDs. In the median LRD, BH*s account\r\nfor ∼ 20% of the UV emission, ∼ 50% at the Balmer break, and ∼ 90% at wavelengths longer\r\nthan Hα with the remainder arising from the host. BH*s preferentially reside in low-mass galaxies\r\n(M⋆ ≈ 108 M⊙) undergoing recent starbursts, as evidenced by extreme emission line EWs (e.g.,\r\n[O III]5008˚A≈ 1100˚A, C III]≈ 12˚A), thereby favoring BH* origins linked to star-formation. We show\r\nV-shaped LRD selections are biased to high BH*/host fractions (≳ 60% at 5500˚A) – less dominant\r\nBH*s may be powering JWST’s blue broad-line AGN. We find BH*s are so commonplace and transient\r\n(duty cycle ∼ 1%, lifetime ∼ 10 Myrs) that every massive black hole may have once shone as a BH*.\r\n"}],"article_type":"original","quality_controlled":"1","article_processing_charge":"No","fulldoi":"https://doi.org/10.33232/001c.162505","type":"journal_article","DOAJ_listed":"1","tmp":{"name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","image":"/images/cc_by.png","short":"CC BY (4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode"},"publisher":"Maynooth Academic Publishing","scopus_import":"1","publication_status":"published","oa_version":"Published Version","volume":9},{"author":[{"last_name":"Torralba Torregrosa","id":"018f0249-0e87-11f0-b167-cbce08fbd541","first_name":"Alberto","full_name":"Torralba Torregrosa, Alberto","orcid":"0000-0001-5586-6950"},{"first_name":"Jorryt J","id":"7439a258-f3c0-11ec-9501-9df22fe06720","last_name":"Matthee","orcid":"0000-0003-2871-127X","full_name":"Matthee, Jorryt J"},{"first_name":"Gabriele","last_name":"Pezzulli","full_name":"Pezzulli, Gabriele"},{"last_name":"Urrutia","first_name":"Tanya","full_name":"Urrutia, Tanya"},{"last_name":"Gronke","first_name":"Max","full_name":"Gronke, Max"},{"first_name":"Sara","id":"edaf889c-c7cd-11ef-ab1b-bb28c431bd29","last_name":"Mascia","full_name":"Mascia, Sara"},{"full_name":"D’Eugenio, Francesco","first_name":"Francesco","last_name":"D’Eugenio"},{"first_name":"Claudia","last_name":"Di Cesare","id":"2d002343-372f-11ef-98ec-a164d20427cb","full_name":"Di Cesare, Claudia"},{"full_name":"Eilers, Anna Christina","first_name":"Anna Christina","last_name":"Eilers"},{"first_name":"Jenny E.","last_name":"Greene","full_name":"Greene, Jenny E."},{"orcid":"0000-0001-8386-3546","full_name":"Iani, Edoardo","first_name":"Edoardo","last_name":"Iani","id":"4053390a-6b68-11ef-9828-a3b8adef8d0a"},{"last_name":"Ishikawa","first_name":"Yuzo","full_name":"Ishikawa, Yuzo"},{"full_name":"Mackenzie, Ruari","last_name":"Mackenzie","first_name":"Ruari"},{"full_name":"Naidu, Rohan P.","last_name":"Naidu","first_name":"Rohan P."},{"first_name":"Benjamín","id":"aa14a535-50c9-11ef-b52e-e0c373d10148","last_name":"Navarrete","full_name":"Navarrete, Benjamín"},{"full_name":"Kotiwale, Gauri","first_name":"Gauri","id":"1438afc8-1ff6-11ee-9fa6-cd4a75d66875","last_name":"Kotiwale"}],"oa":1,"has_accepted_license":"1","month":"01","external_id":{"arxiv":["2505.09542"]},"department":[{"_id":"JoMa"},{"_id":"GradSch"}],"date_created":"2026-01-25T23:01:41Z","citation":{"ista":"Torralba Torregrosa A, Matthee JJ, Pezzulli G, Urrutia T, Gronke M, Mascia S, D’Eugenio F, Di Cesare C, Eilers AC, Greene JE, Iani E, Ishikawa Y, Mackenzie R, Naidu RP, Navarrete B, Kotiwale G. 2026. A weak Ly α halo for an extremely bright little red dot. Indications of enshrouded supermassive black hole growth. Astronomy &#38; Astrophysics. 705, A147.","chicago":"Torralba Torregrosa, Alberto, Jorryt J Matthee, Gabriele Pezzulli, Tanya Urrutia, Max Gronke, Sara Mascia, Francesco D’Eugenio, et al. “A Weak Ly α Halo for an Extremely Bright Little Red Dot. Indications of Enshrouded Supermassive Black Hole Growth.” <i>Astronomy &#38; Astrophysics</i>. EDP Sciences, 2026. <a href=\"https://doi.org/10.1051/0004-6361/202555596\">https://doi.org/10.1051/0004-6361/202555596</a>.","ieee":"A. Torralba Torregrosa <i>et al.</i>, “A weak Ly α halo for an extremely bright little red dot. Indications of enshrouded supermassive black hole growth,” <i>Astronomy &#38; Astrophysics</i>, vol. 705. EDP Sciences, 2026.","mla":"Torralba Torregrosa, Alberto, et al. “A Weak Ly α Halo for an Extremely Bright Little Red Dot. Indications of Enshrouded Supermassive Black Hole Growth.” <i>Astronomy &#38; Astrophysics</i>, vol. 705, A147, EDP Sciences, 2026, doi:<a href=\"https://doi.org/10.1051/0004-6361/202555596\">10.1051/0004-6361/202555596</a>.","ama":"Torralba Torregrosa A, Matthee JJ, Pezzulli G, et al. A weak Ly α halo for an extremely bright little red dot. Indications of enshrouded supermassive black hole growth. <i>Astronomy &#38; Astrophysics</i>. 2026;705. doi:<a href=\"https://doi.org/10.1051/0004-6361/202555596\">10.1051/0004-6361/202555596</a>","short":"A. Torralba Torregrosa, J.J. Matthee, G. Pezzulli, T. Urrutia, M. Gronke, S. Mascia, F. D’Eugenio, C. Di Cesare, A.C. Eilers, J.E. Greene, E. Iani, Y. Ishikawa, R. Mackenzie, R.P. Naidu, B. Navarrete, G. Kotiwale, Astronomy &#38; Astrophysics 705 (2026).","apa":"Torralba Torregrosa, A., Matthee, J. J., Pezzulli, G., Urrutia, T., Gronke, M., Mascia, S., … Kotiwale, G. (2026). A weak Ly α halo for an extremely bright little red dot. Indications of enshrouded supermassive black hole growth. <i>Astronomy &#38; Astrophysics</i>. EDP Sciences. <a href=\"https://doi.org/10.1051/0004-6361/202555596\">https://doi.org/10.1051/0004-6361/202555596</a>"},"OA_type":"diamond","year":"2026","status":"public","PlanS_conform":"1","day":"14","language":[{"iso":"eng"}],"_id":"21045","arxiv":1,"title":"A weak Ly α halo for an extremely bright little red dot. Indications of enshrouded supermassive black hole growth","ddc":["520"],"user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","date_updated":"2026-07-08T06:38:23Z","date_published":"2026-01-14T00:00:00Z","file_date_updated":"2026-02-16T07:35:03Z","publication_identifier":{"issn":["0004-6361"],"eissn":["1432-0746"]},"intvolume":"       705","das_tickbox":"1","OA_place":"publisher","abstract":[{"lang":"eng","text":"The abundant population of little red dots (LRDs), compact objects with red UV to optical colors and broad Balmer lines at high redshift, is revealing new insights into the properties of early active galactic nuclei (AGN). Perhaps the most surprising features of this population are the presence of Balmer absorption and ubiquitous strong Balmer breaks. Recent models link these features to an active supermassive black hole (SMBH) cocooned in very dense gas (NH ∼ 1024 cm−2). We present a stringent test of such models using VLT/MUSE observations of A2744-45924, the most luminous LRD known to date (LHα ≈ 1044 erg s−1), located behind the Abell-2744 lensing cluster at z = 4.464 (μ = 1.8). We detect a moderately extended Lyα nebula (h ≈ 5.7 pkpc), spatially offset from the point-like Hα seen by JWST by ≈1.6 pkpc. The Lyα emission is narrow (FWHM = 270 ± 15 km s−1), and faint (Lyα = 0.07Hα) compared to Lyα nebulae typically observed around quasars of similar luminosity. We detect compact N IV]λ1486 emission, spatially aligned with Hα, and a spatial shift in the far-UV continuum matching the Lyα offset. We discuss that Hα and Lyα have distinct physical origins: Hα originates from the AGN, while Lyα is powered by star formation. In the environment of A2744-45924, we identified four extended Lyα halos (Δz < 0.02, Δr < 100 pkpc). Their Lyα luminosities match the expectations based on Hα emission, and show no evidence for radiation from A2744-45924 affecting its surroundings. The lack of strong, compact, and broad Lyα and the absence of a luminous extended halo, suggest that the UV AGN light is obscured by dense gas cloaking the SMBH with a covering factor close to unity."}],"article_type":"original","project":[{"name":"Young galaxies as tracers and agents of cosmic reionization","grant_number":"101076224","_id":"bd9b2118-d553-11ed-ba76-db24564edfea"}],"publication":"Astronomy & Astrophysics","article_processing_charge":"No","quality_controlled":"1","acknowledgement":"We thank the anonymous referee for constructive and useful comments. We thank Sebastiano Cantalupo for comments on the draft. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 114.27M6.001. Funded by the European Union (ERC, AGENTS, 101076224). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them. We acknowledge funding from JWST program GO-3516. This work is based in part on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These observations are associated with program #3516. MG thanks the Max Planck Society for support through the MPRG. FDE acknowledges support by the Science and Technology Facilities Council (STFC), by the ERC through Advanced Grant 695671 “QUENCH”, and by the UKRI Frontier Research grant RISEandFALL. TU acknowledges funding from the ERC-AdG grant SPECMAP-CGM, GA 101020943. GK acknowledges support from the MERAC foundation.","doi":"10.1051/0004-6361/202555596","file":[{"date_created":"2026-02-16T07:35:03Z","date_updated":"2026-02-16T07:35:03Z","content_type":"application/pdf","access_level":"open_access","file_name":"2026_AstronomyAstrophysics_Torralba.pdf","file_size":2259914,"checksum":"3782e03bc0843438aae8487f6af779c5","creator":"dernst","file_id":"21224","success":1,"relation":"main_file"}],"publication_status":"published","oa_version":"Published Version","corr_author":"1","article_number":"A147","volume":705,"fulldoi":"https://doi.org/10.1051/0004-6361/202555596","type":"journal_article","scopus_import":"1","tmp":{"name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","image":"/images/cc_by.png","short":"CC BY (4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode"},"publisher":"EDP Sciences"},{"external_id":{"arxiv":["2603.28335"]},"month":"07","oa":1,"has_accepted_license":"1","author":[{"full_name":"Torralba Torregrosa, Alberto","orcid":"0000-0001-5586-6950","id":"018f0249-0e87-11f0-b167-cbce08fbd541","last_name":"Torralba Torregrosa","first_name":"Alberto"},{"full_name":"Matthee, Jorryt J","orcid":"0000-0003-2871-127X","first_name":"Jorryt J","last_name":"Matthee","id":"7439a258-f3c0-11ec-9501-9df22fe06720"},{"full_name":"Weibel, Andrea","first_name":"Andrea","last_name":"Weibel"},{"last_name":"Naidu","first_name":"Rohan P.","full_name":"Naidu, Rohan P."},{"full_name":"Ma, Yilun","first_name":"Yilun","last_name":"Ma"},{"first_name":"Aidan P.","last_name":"Cloonan","full_name":"Cloonan, Aidan P."},{"full_name":"Desai, Aayush A","first_name":"Aayush A","last_name":"Desai","id":"502cfd30-32c1-11ee-a9a4-d8dad5c6739e"},{"full_name":"De Graaff, Anna","last_name":"De Graaff","first_name":"Anna"},{"last_name":"Greene","first_name":"Jenny E.","full_name":"Greene, Jenny E."},{"last_name":"Jespersen","first_name":"Christian Kragh","full_name":"Jespersen, Christian Kragh"},{"full_name":"Kramarenko, Ivan","orcid":"0000-0001-5346-6048","id":"9a9394cb-3200-11ee-973b-f5ba2a8b16e4","last_name":"Kramarenko","first_name":"Ivan"},{"first_name":"Sara","id":"edaf889c-c7cd-11ef-ab1b-bb28c431bd29","last_name":"Mascia","full_name":"Mascia, Sara"},{"last_name":"Oesch","first_name":"Pascal A.","full_name":"Oesch, Pascal A."},{"last_name":"Sun","first_name":"Wendy Q.","full_name":"Sun, Wendy Q."},{"full_name":"Williams, Christina C.","first_name":"Christina C.","last_name":"Williams"}],"status":"public","date_created":"2026-07-12T22:02:17Z","citation":{"mla":"Torralba Torregrosa, Alberto, et al. “A Black Hole Star at Cosmic Noon: Extreme Balmer Break, Photospheric Continuum, and Broad Absorption by Thick Winds in a Little Red Dot at z = 1.7.” <i>The Astrophysical Journal Letters</i>, vol. 1005, no. 2, L37, IOP Publishing, 2026, doi:<a href=\"https://doi.org/10.3847/2041-8213/ae7bfd\">10.3847/2041-8213/ae7bfd</a>.","ama":"Torralba Torregrosa A, Matthee JJ, Weibel A, et al. A black hole star at cosmic noon: Extreme Balmer break, photospheric continuum, and broad absorption by thick winds in a Little Red Dot at z = 1.7. <i>The Astrophysical Journal Letters</i>. 2026;1005(2). doi:<a href=\"https://doi.org/10.3847/2041-8213/ae7bfd\">10.3847/2041-8213/ae7bfd</a>","short":"A. Torralba Torregrosa, J.J. Matthee, A. Weibel, R.P. Naidu, Y. Ma, A.P. Cloonan, A.A. Desai, A. De Graaff, J.E. Greene, C.K. Jespersen, I. Kramarenko, S. Mascia, P.A. Oesch, W.Q. Sun, C.C. Williams, The Astrophysical Journal Letters 1005 (2026).","apa":"Torralba Torregrosa, A., Matthee, J. J., Weibel, A., Naidu, R. P., Ma, Y., Cloonan, A. P., … Williams, C. C. (2026). A black hole star at cosmic noon: Extreme Balmer break, photospheric continuum, and broad absorption by thick winds in a Little Red Dot at z = 1.7. <i>The Astrophysical Journal Letters</i>. IOP Publishing. <a href=\"https://doi.org/10.3847/2041-8213/ae7bfd\">https://doi.org/10.3847/2041-8213/ae7bfd</a>","chicago":"Torralba Torregrosa, Alberto, Jorryt J Matthee, Andrea Weibel, Rohan P. Naidu, Yilun Ma, Aidan P. Cloonan, Aayush A Desai, et al. “A Black Hole Star at Cosmic Noon: Extreme Balmer Break, Photospheric Continuum, and Broad Absorption by Thick Winds in a Little Red Dot at z = 1.7.” <i>The Astrophysical Journal Letters</i>. IOP Publishing, 2026. <a href=\"https://doi.org/10.3847/2041-8213/ae7bfd\">https://doi.org/10.3847/2041-8213/ae7bfd</a>.","ista":"Torralba Torregrosa A, Matthee JJ, Weibel A, Naidu RP, Ma Y, Cloonan AP, Desai AA, De Graaff A, Greene JE, Jespersen CK, Kramarenko I, Mascia S, Oesch PA, Sun WQ, Williams CC. 2026. A black hole star at cosmic noon: Extreme Balmer break, photospheric continuum, and broad absorption by thick winds in a Little Red Dot at z = 1.7. The Astrophysical Journal Letters. 1005(2), L37.","ieee":"A. Torralba Torregrosa <i>et al.</i>, “A black hole star at cosmic noon: Extreme Balmer break, photospheric continuum, and broad absorption by thick winds in a Little Red Dot at z = 1.7,” <i>The Astrophysical Journal Letters</i>, vol. 1005, no. 2. IOP Publishing, 2026."},"OA_type":"gold","year":"2026","department":[{"_id":"JoMa"},{"_id":"IlCa"},{"_id":"GradSch"}],"title":"A black hole star at cosmic noon: Extreme Balmer break, photospheric continuum, and broad absorption by thick winds in a Little Red Dot at z = 1.7","arxiv":1,"_id":"22263","language":[{"iso":"eng"}],"day":"10","issue":"2","das_tickbox":"1","OA_place":"publisher","file_date_updated":"2026-07-13T07:46:22Z","publication_identifier":{"issn":["2041-8205"],"eissn":["2041-8213"]},"intvolume":"      1005","supplementarymaterial":"yes","ddc":["520"],"date_published":"2026-07-10T00:00:00Z","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","date_updated":"2026-07-13T08:08:41Z","quality_controlled":"1","article_processing_charge":"Yes","project":[{"grant_number":"101076224","name":"Young galaxies as tracers and agents of cosmic reionization","_id":"bd9b2118-d553-11ed-ba76-db24564edfea"}],"publication":"The Astrophysical Journal Letters","researchdata_availability":"yes","article_type":"original","abstract":[{"text":"Recent studies at high redshift have revealed an enigmatic class of little red dots (LRDs) with extreme Balmer breaks, stronger than in any stellar atmosphere. However, it is unclear whether such objects exist at lower redshift, especially given the low number of LRDs reported at z ≲ 2. Here, we report the discovery of PAN-BH*-1, an LRD with an extreme Balmer break at z = 1.73, identified from JWST/NIRCam pure-parallel imaging taken by the PANORAMIC survey, and confirmed by deep VLT/X-Shooter spectroscopy. The rest-optical to near-infrared spectral energy distribution of PAN-BH*-1 is consistent with a photospheric continuum with effective temperature Teff ≈ 4800 K. The broad Hα emission line shows remarkably deep absorption, stronger than previously measured in any LRD. The absorption trough spans from −520 to +267 km s−1 with respect to the systemic redshift. The presence of blue- and red-shifted absorption suggests complex dynamics of the obscuring gas along the line of sight. We speculate that the absorption trough can be produced by a thick wind launched from a thick, rotating photospheric disk, the latter being the source of the red optical continuum. While the source is unresolved in the rest-optical JWST data (reff < 47 pc), the rest-near-UV Hubble Space Telescope imaging shows an extended morphology with (formular displayed) kpc, which we interpret as a host galaxy with a stellar mass of ∼10^8 M⊙, in line with the narrow Hα emission. The discovery of this object at cosmic noon highlights the feasibility of systematic searches for extreme LRDs with wide-area facilities such as Euclid and Roman.","lang":"eng"}],"file":[{"date_created":"2026-07-13T07:46:22Z","date_updated":"2026-07-13T07:46:22Z","access_level":"open_access","content_type":"application/pdf","success":1,"file_id":"22274","file_size":5419071,"file_name":"2026_AstrophysicalJourLetters_Torralba.pdf","creator":"dernst","checksum":"7600db260d799ddea45cf3bd01effe41","relation":"main_file"}],"doi":"10.3847/2041-8213/ae7bfd","acknowledgement":"IOP Science home\r\nThe Astrophysical Journal Letters\r\nThe American Astronomical Society, find out more.\r\n\r\nThe following article isOpen access\r\nA Black Hole Star at Cosmic Noon: Extreme Balmer Break, Photospheric Continuum, and Broad Absorption by Thick Winds in a Little Red Dot at z = 1.7\r\nAlberto Torralba, Jorryt Matthee, Andrea Weibel, Rohan P. Naidu, Yilun Ma, Aidan P. Cloonan, Aayush Desai, Anna de Graaff, Jenny E. Greene, Christian Kragh JespersenShow full author list\r\n\r\nPublished 2026 June 30 • © 2026. The Author(s). Published by the American Astronomical Society.\r\nThe Astrophysical Journal Letters, Volume 1005, Number 2\r\nCitation Alberto Torralba et al 2026 ApJL 1005 L37\r\nDOI 10.3847/2041-8213/ae7bfd\r\n\r\nPDFOpens in a new tab.ePub\r\nAuthors\r\nFigures\r\nTables\r\nReferences\r\nArticle data\r\nPDFOpens in a new tab.ePub\r\nArticle metrics\r\n122 Total downloads\r\n\r\nShare this article\r\nArticle information\r\nAbstract\r\nRecent studies at high redshift have revealed an enigmatic class of little red dots (LRDs) with extreme Balmer breaks, stronger than in any stellar atmosphere. However, it is unclear whether such objects exist at lower redshift, especially given the low number of LRDs reported at z ≲ 2. Here, we report the discovery of PAN-BH*-1, an LRD with an extreme Balmer break at z = 1.73, identified from JWST/NIRCam pure-parallel imaging taken by the PANORAMIC survey, and confirmed by deep VLT/X-Shooter spectroscopy. The rest-optical to near-infrared spectral energy distribution of PAN-BH*-1 is consistent with a photospheric continuum with effective temperature Teff ≈ 4800 K. The broad Hα emission line shows remarkably deep absorption, stronger than previously measured in any LRD. The absorption trough spans from −520 to +267 km s−1 with respect to the systemic redshift. The presence of blue- and red-shifted absorption suggests complex dynamics of the obscuring gas along the line of sight. We speculate that the absorption trough can be produced by a thick wind launched from a thick, rotating photospheric disk, the latter being the source of the red optical continuum. While the source is unresolved in the rest-optical JWST data (reff < 47 pc), the rest-near-UV Hubble Space Telescope imaging shows an extended morphology with \r\n kpc, which we interpret as a host galaxy with a stellar mass of ∼108 M⊙, in line with the narrow Hα emission. The discovery of this object at cosmic noon highlights the feasibility of systematic searches for extreme LRDs with wide-area facilities such as Euclid and Roman.\r\n\r\nExport citation and abstract\r\nBibTeXRIS\r\n\r\nPrevious article in issue\r\nNext article in issue\r\n\r\nOriginal content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.\r\n\r\n1. Introduction\r\nThe unprecedented sensitivity of JWST has enabled the discovery of a new, abundant population of objects at redshifts z ≈ 3–9 nicknamed the “little red dots” (LRDs). These are characterized by their compact rest-frame optical morphology, broad emission lines, and a characteristic rest-UV to optical “V-shape” in their spectral energy distributions (SED; e.g., D. D. Kocevski et al. 2023; V. Kokorev et al. 2024; J. Matthee et al. 2024; I. Labbe et al. 2025).\r\n\r\nThe nature of LRDs is highly debated (see K. Inayoshi & L. C. Ho 2025, for a recent overview) as the LRDs show systematic differences with respect to other types of active galactic nuclei (AGN), such as faintness in X-rays (e.g., T. T. Ananna et al. 2024; M. Yue et al. 2024), mid-to-far-infrared dust emission (e.g., G. C. K. Leung et al. 2025; C. C. Williams et al. 2024; I. Delvecchio et al. 2025; D. J. Setton et al. 2025; M. Xiao et al. 2025), and radio (e.g., G. Mazzolari et al. 2026; M. A. Latif et al. 2025; K. Perger et al. 2025, see A. J. Gloudemans et al. 2025).\r\n\r\nA recurring spectral feature of LRDs is the presence of a strong Balmer break (e.g., D. J. Setton et al. 2025; B. Wang et al. 2024; R. E. Hviding et al. 2025; W. Q. Sun et al. 2026), in some cases stronger than any star or stellar population can produce. The two most prominent examples known to date are The Cliff at z ≈ 3.5 (A. de Graaff et al. 2025a) and MoM-BH* at z ≈ 7.8 (R. P. Naidu et al. 2025). The joint appearance of strong Balmer lines as well as strong Balmer breaks has been modeled as being due to absorption by a dense, neutral gas with a high column density in the line of sight to a highly ionizing source (K. Inayoshi & R. Maiolino 2025; X. Ji et al. 2025; A. Sneppen et al. 2026; A. Torralba et al. 2026). These observations have sparked the development of new theoretical models, ranging from a spherical envelope analogous to stellar atmospheres (e.g., M. C. Begelman & J. Dexter 2026; D. Kido et al. 2025; H. Liu et al. 2025; D. Nandal & A. Loeb 2026) or a thick accretion disk (e.g., H. Liu et al. 2025, 2026; K. Inayoshi et al. 2025; Y.-X. Chen et al. 2026).\r\n\r\nBesides their spectral features, the evolution of the LRD number densities is also in stark contrast to other types of AGNs (e.g., K. Inayoshi 2025). At 4 ≲ z ≲ 7, LRDs represent a few percent of the galaxy population (e.g., D. D. Kocevski et al. 2023, 2025; J. E. Greene et al. 2024; V. Kokorev et al. 2024; X. Lin et al. 2024; R. Maiolino et al. 2024; J. Matthee et al. 2024), with number densities of ≳10−5 Mpc−3. The number density does not appear to drop quickly beyond z > 5 (e.g., J. Zhang et al. 2026), with various LRDs having been confirmed at z  >  8 (V. Kokorev et al. 2023; A. J. Taylor et al. 2025; R. Tripodi et al. 2025), well beyond the quasar redshift record (F. Wang et al. 2021). Photometric LRD candidates exist beyond z  >  10 (T. S. Tanaka et al. 2025). In turn, the number density of LRDs seems to decline steeply at z  <  4 (e.g., Y. Ma et al. 2026), with estimates of a number density of ∼10−6 cMpc−3 at z ∼ 2 and even ∼10−10 cMpc−3 at z ≈ 0.3 (X. Lin et al. 2026). While it is challenging to ensure a uniform selection function across such a large redshift baseline and dedicated spectroscopic follow-up of such lower redshift candidates has only just started, it is challenging to attribute five orders of magnitude to such effects.\r\n\r\nMotivated by the discovery of rare objects with extreme Balmer breaks at z  >  3 and the very small number of known LRDs at lower redshift, we performed a dedicated search for extreme Balmer break objects using a template-match approach on a large compilation of JWST NIRCam data over ≈0.3 deg2 and z ≈ 1.5–7.0. This survey is presented in A. Weibel et al. (2026a). As part of an ongoing ground-based spectroscopic campaign of LRD candidates at z ∼ 2 (Y. Ma et al. 2026), we followed up the most luminous candidate with a photometric redshift of z ≈ 2 with the X-Shooter spectrograph on the Very Large Telescope (VLT). In this Letter, we present the discovery and spectroscopic confirmation of PAN-BH*-1, a luminous LRD at z = 1.73 with an extreme Balmer break comparable to the strongest observed in any LRD (and, in general, any astrophysical source). The low redshift of this source enables high-resolution spectroscopy from ground-based observatories that is otherwise impossible to obtain at high redshift.\r\n\r\nThroughout this Letter, we use a ΛCDM cosmology with Ωm = 0.31, ΩΛ = 0.69, and h = 0.677 as described by Planck Collaboration et al. (2020). All the magnitudes are given in the AB system (J. B. Oke & J. E. Gunn 1983).\r\n\r\n2. Observations\r\n2.1. Photometry and Source Selection\r\nWe identified PAN-BH*-1 (ID: PAN-1115, RA, DEC: 40.015835, −1.659363 J2000) as part of a systematic search across ≈0.3 deg2 of JWST NIRCam legacy imaging comprising at least six filters of coverage (A. Weibel et al. 2026b). Notably, this dataset includes the Cycle 1 pure parallel survey PANORAMIC (PID: 2514, PIs: Williams & Oesch; C. C. Williams et al. 2025) that contributes 28 of the 35 independent lines of sight, thereby enabling the discovery of rare objects such as PAN-BH*-1 across diverse large-scale structure environments. Specifically, this source was identified in the footprint j024000m0142 of the PANORAMIC DR1,15 which is adjacent to the A370 field (G. O. Abell et al. 1989), where archival images by the Hubble Space Telescope (HST) are available from the BUFFALO survey (C. L. Steinhardt et al. 2020). The HST/ACS images were processed with grizli and also released as part of the PANORAMIC dataset.\r\n\r\nPAN-BH*-1 is in the outskirts of the A370 lensing cluster, but the magnification is only μ ≈ 1.05 according to the models from A. Niemiec et al. (2023). Throughout the rest of the paper, we report the uncorrected flux measurements, since the effect of magnification (∼5%) is negligible given the uncertainties in the observations and the lensing model.\r\n\r\nThe search strategy and full photometric selection are described in a companion paper (A. Weibel et al. 2026a). Briefly, that work presents a new selection of LRDs as a combination of a “black hole star” template (BH*; R. P. Naidu et al. 2025) embedded in a host galaxy, instead of the typically used “V-shaped” selections (e.g., D. D. Kocevski et al. 2025; V. Kokorev et al. 2024). The host galaxies are modeled using eazy’s blue_sfhz templates. The BH*s are modeled using a novel template set comprising empirical luminosity-based stacks constructed in W. Q. Sun et al. (2026), the cloudy template from R. P. Naidu et al. (2025), and by using spectra of prominent LRDs spanning the observed effective temperature range (I. Labbe et al. 2024; A. de Graaff et al. 2025a; B. Wang et al. 2026).\r\n\r\nPAN-BH*-1 stood out as one of the few sources where the BH* template effectively dominated all the light over the full wavelength range covered by NIRCam (hence the name). The redshift of PAN-BH*-1 was estimated to be zphot = 1.85. Follow-up VLT/X-Shooter spectroscopy confirmed the redshift as zspec = 1.731 (see Section 3.2).\r\n\r\nPAN-BH*-1 is also covered by archival data from the VLT with the HAWK-I camera in the Ks band (G. B. Brammer et al. 2016) and in data from the Spitzer Space Telescope in IRAC bands 1 and 3 (3.6 and 5.7 μm), and MIPS 24 μm (P. Capak 2019). PAN-BH*-1 is detected in the Ks band and in the two IRAC filters. Performing Spitzer photometry of this source is challenging due to the large point spread function (PSF) and a neighboring source, especially in the MIPS band. However, the NIRCam photometry of the neighboring source suggests it has a limited contribution to the IRAC fluxes. The details of the photometry extraction are described in Appendix A, and the measured magnitudes in Table 2.\r\n\r\n2.2. VLT/X-Shooter Spectroscopy\r\nPAN-BH*-1 was observed for 5.8 ks with the X-Shooter spectrograph (J. Vernet et al. 2011) on the VLT as a bright backup target for program 116.294D (PI: Matthee) in visitor mode on 2025 December 17. The main aim of this program was to confirm candidate LRDs at cosmic noon (Y. Ma et al. 2026). These observations confirmed the redshift through the detection of Hα at z = 1.731. A DDT program (ID 116.2AQ0; PI: Matthee) obtained additional follow-up data of PAN-BH*-1 in service mode for 26.2 ks during 2026 January 10–26, yielding a total exposure time of 8.9 hr. X-Shooter observes with three arms simultaneously, UVB, VIS, and near-infrared (NIR), covering rest-frame wavelengths of ≈0.14–0.9 μm, albeit hampered by skyline emission and telluric absorption, primarily in the rest-frame optical.\r\n\r\nThe observing conditions were clear, with a seeing ranging from 05 to 07 (median 06). The service mode observations were primarily conducted during dark nights, with some gray (FLI = 0.03–0.6, median 0.1), and a typical airmass of 1.35. We used UVB, VIS, and NIR slits with widths 10, 09, and 09, yielding a nominal resolution of R = 5400, 8900, and 5600, respectively (FWHM ∼53 km s−1 for NIR). The target acquisition was done using blind offsets from a reference star, due to the target being too faint for direct acquisition. We used a standard nodding on the slit pattern, with 4″ nod throws in an ABBA pattern, and 1″ jitters in the NIR arm to improve the sky subtraction. In each observing block of ≈1 hr, the exposure times were 700, 655, and (2×)365 s for the three arms at each nod position.\r\n\r\nThe reduction of the X-Shooter data uses a combination of EsoRex libraries16 and Python code based on the reduction pipeline employed in J. Matthee et al. (2021). Each observing block was reduced separately. We used standard stars taken during the observing night for a first-pass flux calibration. Telluric corrections were applied using the molecfit tool (A. Smette et al. 2015) implemented in the X-Shooter EsoRex pipeline. Telluric stars were observed during the visitor nights, but they were not always observed during the service mode observations in January. For those observations, we took the telluric star that was observed at the closest observing date. Based on the variation in telluric absorption among the reference stars taken during this period, we estimate the variation in the transmission and propagate the uncertainty in the telluric correction. For each observing block, we then extracted an optimally extracted 1D spectrum using the spatial profile of the Hα line, thus accounting for seeing variations and (more importantly) minor errors in the accuracy of the slit pointing. Before median combining these spectra, we normalize them by the median Hα flux of all observations to account for variations in slit losses and flux calibrations.\r\n\r\nBesides Hα (integrated S/N = 75) and Hβ (integrated S/N = 6; Section 3.2), we also detect continuum emission in the best regions in the H and K bands at 1.6 μm and 2.1 μm, respectively, with a low signal-to-noise ratio (S/N) of ∼1 per resolution element. Unfortunately, the [O iii] λλ4960, 5008 doublet is undetectable because the observed wavelengths are impacted by very strong telluric absorption. No other lines or continuum are detected in the X-Shooter spectrum.\r\n\r\n3. Properties of PAN-BH*-1\r\n3.1. Spectral Shape: A Photospheric Continuum with Strong Hα Emission\r\nThe photometric SED of PAN-BH*-1 has remarkable similarities with The Cliff (Figure 1): luminous in the rest optical, with a sudden drop toward the rest-UV around the Balmer limit, and very weak near-to-mid infrared continuum emission. With a rough extrapolation of the two HST photometric points using a power-law fit (fλ ∝ λβ), we obtain a UV slope of β = −0.1 ± 1.2, and MUV = −16.7 ± 0.7. For the rest-frame optical to NIR data, we fit a Planck blackbody law to the JWST data points, after subtracting the measured Hα flux (see Section 3.2) from the F200W photometry. The rest-optical and NIR photometry of PAN-BH*-1 is remarkably well described by a single temperature blackbody with T = 4204 K (with a best-fit ). We measure the strength of the Balmer break from the fν ratio F115W/F814W = 7 ± 1, in line with the Balmer break strengths of The Cliff (; A. de Graaff et al. 2025a)17 and MoM-BH* (7.8 ± 1.8; R. P. Naidu et al. 2025), measured from JWST/NIRSpec PRISM spectra as fν,4000–4100/fν,3620−3720. In Figure 2, we compare the Balmer break strength with the spectroscopic sample of A. de Graaff et al. (2025b), showing that out of 134 sources, only two have breaks significantly above 5. This suggests that PAN-BH*-1 has among the most extreme Balmer breaks known, although we caution that our value is derived from wide-band photometry with pivot wavelengths corresponding to 4212 and 3042 Å, respectively, rather than from spectroscopy.\r\n\r\nZoom InZoom OutReset image size\r\nFigure 1. SED of PAN-BH*-1 Top: cutouts from all the HST and JWST images in which PAN-BH*-1 is covered. It shows a remarkably compact morphology in all the wavelengths, resolved only in the HST F606W and F814W bands (Section 3.3). Bottom: photometry from JWST/NIRCam (blue squares), HST/ACS (purple pentagons), and Spitzer/IRAC+MIPS (red hexagons, and red triangle for the 5σ upper limit). The empty square is the F200W flux after subtracting the Hα flux measured from X-Shooter spectroscopy. We show the spectrum of The Cliff for comparison (gray line), shifted to z = 1.73 and normalized to the F150W flux of PAN-BH*-1. We also show the best-fitting blackbody spectrum (blue dashed line) and the best model from the synthetic LRD atmosphere models from H. Liu et al. (2026), shifted to z = 1.73 (green line), undersampled by a factor of 500 for clarity.\r\n\r\nDownload figure:\r\n\r\nStandard imageHigh-resolution image\r\nZoom InZoom OutReset image size\r\nFigure 2. Spectroscopic sample of LRDs by redshift and Balmer break strength. We plot the redshift and Balmer break strength of PAN-BH*-1, and the JWST sample from A. de Graaff et al. (2025b) (purple diamonds), and three local LRDs in X. Lin et al. (2026), for comparison. We also highlight three sources with a particularly strong Balmer break: The Cliff (A. de Graaff et al. 2025a), MoM-BH* (R. P. Naidu et al. 2025), and CAPERS-LRDz9 (A. J. Taylor et al. 2025). The Balmer break strength of the JWST spectroscopic sample is computed as fν,4000–4100/fν,3620–3720, whereas the value for PAN-BH*-1 is directly obtained from the F115W/F814W photometry.\r\n\r\nDownload figure:\r\n\r\nStandard imageHigh-resolution image\r\n3.2. Hα and Hβ Emission Lines\r\nThe Hα profile appears as a complex combination of a broad line with strong absorption close to the systemic redshift. We fit the Hα emission line with a similar model as the one used in A. Torralba et al. (2026) and J. Matthee et al. (2026). The Hα model consists of two Gaussian emission components (with narrow and intermediate line widths), and a broad symmetric exponential convolved with the intermediate profile and parameterized as in F. D’Eugenio et al. (2025a). The absorption is implemented as an opacity law defined as e−τ(λ), where τ(λ) also follows a single Gaussian velocity distribution (F. D’Eugenio et al. 2025a, 2025b; A. Torralba et al. 2026). For simplicity, we assume a covering factor of Cf = 1 for the absorbing gas. In previous works, the width of the narrow component is tied to that of [O iii], assuming both components come from the same region, often interpreted as the interstellar medium (ISM) of the host galaxy. In this case, we have no information about [O iii] due to this doublet falling in a wavelength range heavily affected by strong telluric absorption. We fit the Hα line after masking relevant skylines and strong telluric absorption bands. The fitted Hα parameters are listed in Table 1 and the best-fit model is shown in Figure 3. The absorption feature is notably strong, with an equivalent width of EWabs = −148 ± 12 Å with respect to the fitted continuum and 12.2 ± 0.2 Å if including the broad emission component. The absorption corresponds to a Balmer optical depth at the line center of , reaching roughly the continuum level. The FWHM of the single Gaussian fitted to the absorber is 283  ±  8 km s−1, and is offset from the systemic redshift by −94 ± 4 km s−1. We note that this parameterization is somewhat arbitrary, and we discuss in detail the absorber properties in Section 4.\r\n\r\nZoom InZoom OutReset image size\r\nFigure 3. Hα spectrum, and the best fit to our fiducial model. We show the X-Shooter R ∼ 5600 spectrum of the Hα line of PAN-BH*-1, along with the best-fit to the model described in Section 3.2; total model (red solid line) and individual components (discontinuous color lines). The red wing of the line is severely affected by telluric absorption, thus the large uncertainties.\r\n\r\nDownload figure:\r\n\r\nStandard imageHigh-resolution image\r\nTable 1. Properties of PAN-BH*-1\r\n\r\nParameter\tValue\tUnit\r\nWidth (FWHM; Hα)\r\nExponential\t1257 ± 27\tkm s−1\r\nIntermediate\t687 ± 43\tkm s−1\r\nNarrow\t184 ± 12\tkm s−1\r\nAbsorption\t283 ± 8\tkm s−1\r\nFlux (Hα)\r\nExponential\t643 ± 7\t10−18 erg s−1 cm−2\r\nIntermediate\t19 ± 5\t10−18 erg s−1 cm−2\r\nNarrow\t38 ± 3\t10−18 erg s−1 cm−2\r\nTotal\t522 ± 7\t10−18 erg s−1 cm−2\r\nGeneral properties\r\n(LHα/erg s−1)\t43.046 ± 0.006\t⋯\r\nEW0(Hα)\t520 ± 20\tÅ\r\nSFR(Hα, narrow)a\t2.1 ± 0.2\tM⊙ yr−1\r\nSFR(Hα, narrow)b\t3.3 ± 0.3\tM⊙ yr−1\r\nreff,UV (F606W+F814W)\t\tkpc\r\nreff,opt (F200W)\t<0.047\tkpc\r\nHα/Hβ (total)\t>9.4\t⋯\r\nHα/Hβ (narrow)\t5 ± 1\t⋯\r\nNotes. aCalibration from I. G. Kramarenko et al. (2026). bCalibration from R. C. Kennicutt & N. J. Evans (2012). SFR values calculated assuming no dust attenuation.\r\n\r\nDownload table as: \r\nASCIITypeset image\r\n\r\nThe Hβ line is marginally detected. After undersampling the spectrum by a factor 5, a hint of a weak narrow component can be identified (Figure 4), along with a tentative absorption at the same mean velocity as in Hα. We fit the best Hα model to the Hβ spectrum, only rescaling it by a multiplicative factor, and adding a flat continuum component. By doing this, we find an Hβ flux of (47 ± 8) × 10−18 erg s−1 cm−2 (S/N ≈ 6). Conservatively, we obtain a Balmer decrement of Hα/Hβ > 9.4 (at a 3σ confidence level), in line with the high decrements found for the LRD population (e.g., G. P. Nikopoulos et al. 2026; A. de Graaff et al. 2025b; J. Matthee et al. 2026). In Figure 5, we show the Hβ spectrum compared to the rescaled Hα model. By matching the best-fit Hα profile with the data at the expected observed wavelength for Hβ (±5000 km s−1), we obtain a better agreement (, BIC = 1537) than fitting a flat continuum only (, BIC = 1658) with ΔBIC = 121 ≫ 10, strongly favoring a detection of a broad Hβ emission line, and securing the spectroscopic redshift. Similarly, we fit a narrow Gaussian to Hβ with the same width and velocity as the Hα best-fit model, assuming a completely saturated absorption. We obtain a Balmer decrement for the narrow component of Hα/Hβ = 5 ± 1, which would imply a dust extinction of using a J. A. Cardelli et al. (1989) attenuation law, under the assumption of case B recombination. However, due to the low S/N of Hβ this result is only tentative, and compatible with a standard Case B value within ∼2σ.\r\n\r\nZoom InZoom OutReset image size\r\nFigure 4. X-Shooter spectrum of Hα and Hβ of PAN-BH*-1 (blue). We compare to the spectrum of The Cliff (gray; data from JWST DDT #9433), normalized in each panel to the flux of PAN-BH*-1 in the range v ∈ (−3000, −2000) km s−1. Due to the low S/N, the Hβ spectrum of PAN-BH*-1 is rebinned to a coarser grid by a factor 5, after masking the most relevant skylines.\r\n\r\nDownload figure:\r\n\r\nStandard imageHigh-resolution image\r\nZoom InZoom OutReset image size\r\nFigure 5. Hβ spectrum. The spectrum is rebinned by a factor of 10 with inverse variance flux weighting for visual clarity, due to the low S/N. We compare to the best-fit Hα model, scaled by a factor of 0.112. In the bottom panel, we show the χ residuals between the spectrum and the rescaled Hα model in black, and for only the continuum in pink (ΔBIC = 121 strongly favoring the presence of a broad Hβ line).\r\n\r\nDownload figure:\r\n\r\nStandard imageHigh-resolution image\r\n3.3. Spatial Morphology\r\nIn order to assess whether PAN-BH*-1 is spatially resolved, we use the Bayesian profile fitting software pysersic (I. Pasha & T. B. Miller 2023)18 to fit a single Sérsic profile to the JWST and HST imaging data of PAN-BH*-1. For JWST/NIRCam, we choose F200W as the filter with the highest S/N in the short wavelength channel, benefiting from a high spatial resolution and probing rest-frame optical wavelengths. To model its PSF, we use version 2.2.0 of the stpsf software (formerly webbpsf, M. D. Perrin et al. 2014). For the two HST bands F606W and F814W, we instead construct empirical PSFs from public imaging data in the GOODS-S field following A. Weibel et al. (2024). In all three bands, we sample the posterior with the No U-turn sampler in two chains with 1000 warm-up and 2000 sampling steps each. We find that PAN-BH*-1 is unresolved with NIRCam in F200W where the effective radius converges toward the edge of the prior at 0.25 pixels. Using the 95th percentile of the posterior chains as an upper limit on the effective radius, we find a rest-optical size of reff < 47 pc.\r\n\r\nPAN-BH*-1 appears to be resolved in the HST images corresponding to rest-frame pivot 0.2 and 0.3 μm, respectively. Due to the low signal-to-noise of the F606W and F814W photometry, we fit both bands simultaneously fixing all the morphological parameters in both images. We measure physical effective radii of  kpc (see Appendix B). The modest stretching by the foreground A370 lensing cluster could imply a correction of ∼10% to the measured radius (A. Niemiec et al. 2023), which we disregard given the uncertainties. These measured sizes are consistent with the typical sizes for galaxies with a stellar mass ≲ 109 M⊙ at z = 1.75 (A. van der Wel et al. 2014). These findings are consistent with the scenario of a compact LRD “engine” dominating the rest-optical light embedded in a host galaxy, whose contribution becomes significant blueward of the Balmer break (see A. P. Cloonan et al. 2026, for a relevant discussion).\r\n\r\n4. Absorber Kinematics\r\nAs described in Section 3.2, the velocity distribution of the absorber is empirically modeled with a Gaussian, which we find has a central velocity of −94 ± 4 km s−1 relative to the redshift of the narrow emission component (adopted as systemic). The absorption trough extends from negative to positive velocities with respect to the redshift of the narrow component, but also with respect to the center of the symmetric exponential wings. However, there are several degeneracies between the shape of the absorber and other components of the emission line, such as the narrow central emission (see Section 3.2). Furthermore, direct interpretation of the absorber center velocity shift is challenging in an optically thick gas with presumably complex dynamics, and it does not necessarily trace bulk motion. A more robust, physically motivated pair of quantities is the minimum and maximum absorber velocities. We define them as the values where the transmission of the Balmer absorber increases to 99%,  km s−1 and  km s−1. These values trace the largest velocities in the line of sight of gas with significant Balmer absorption. The absorbing trough extends over 787 ± 17 km s−1 under this definition. The values of and are relatively agnostic to the choice of the shape of the absorber, since they are determined by the wavelength where the line profile deviates from a broad, symmetric exponential profile. In Figure 6, we illustrate three proposed configurations of the velocity distribution of the absorbing gas that could explain the shape of the observed Balmer absorption, and we discuss these scenarios below.\r\n\r\nZoom InZoom OutReset image size\r\nFigure 6. Geometric configurations for the absorber. We illustrate three scenarios that could give rise to the observed Balmer absorption in PAN-BH*-1. In scenario (a), the obscuring agent is a thick screen of gas with a certain bulk velocity, and turbulent motions produce the broadening of the absorption trough. In (b), there are two (or more) absorbers with opposite velocities in the line of sight. These first two scenarios are dynamically unstable; therefore, variability is expected in the absorption. Lastly, in (c), we observed an extended source through a disk wind with a rotational component (vϕ) in addition to the poloidal (nonazimuthal) velocity (vp). In the last scenario, the redshifted absorption is produced by streamlines that oppose the observer when projected along the line of sight, despite the fact that the gas is outflowing from the central source.\r\n\r\nDownload figure:\r\n\r\nStandard imageHigh-resolution image\r\n4.1. Unstable Gas Flows?\r\nThe fact that there is significant absorption at both negative and positive velocities with respect to the systemic redshift cannot be simply explained by an axisymmetric outflowing or inflowing wind. In the case of observing a compact object through a spherically symmetric, nonturbulent bulk flow, a classical P Cygni profile is expected, with a purely blueshifted absorption (or redshifted if the wind is infalling). The fact that we also see redshifted absorption rules out this simple scenario. In principle, turbulent motions could also produce broadening of the absorbing medium (scenario a in Figure 6). However, the required turbulent velocity dispersion σturb ≈ 120 km s−1 (from the Gaussian fit in Section 3.2) is comparable to the mean velocity of the absorption trough, meaning that turbulence dominates the gas flow. In such a case, strong variability of the absorption profile would be expected, given the typical dynamical crossing times (see Sect. 4.1 in F. D’Eugenio et al. 2025b). For example, for a radius of 1016 cm (e.g., A. Torralba et al. 2026) and a mass of 106 M⊙, the dynamical freefall time is  yr. Moreover, the turbulent velocity would be highly supersonic, and the dissipation timescale would be comparable to the dynamical time (e.g., M.-M. Mac Low 1999). Alternatively, in the context of a strong Balmer absorber at z ∼ 7, F. D’Eugenio et al. (2026) recently discussed a “breathing mode” scenario with cyclic inflows and outflows along the same line of sight, with the gas being in different phases at different depths (scenario b in Figure 6; see also K. Park et al. 2017). In this case, the same arguments regarding the stability of the absorber would apply, and absorber variability is expected on observed timescales of ∼5 yr (for a source at z = 1.7), which is testable with future observations.\r\n\r\n4.2. The Case for the Disk Wind Hypothesis\r\nAn alternative, dynamically stable scenario is a disk wind configuration (scenario c in Figure 6). Here, the wind would be launched from a thick disk near the central engine, which we speculate could be the source of the optical continuum emission (e.g., H. Liu et al. 2025, 2026; L. Zwick et al. 2025; Y.-X. Chen et al. 2026). A rotating disk would imprint to the wind an azimuthal velocity component (vϕ). Observations at specific lines of sight, particularly for high inclination angles (close to edge-on) where the rotational component dominates the poloidal velocity, can give rise to both blueshifted and redshifted absorption features (D. Proga et al. 2000; P. B. Hall et al. 2002, 2013; D. Proga & T. R. Kallman 2004; M. Giustini & D. Proga 2012). Most observed LRDs have blueshifted P Cygni–like absorbers (J. Matthee et al. 2026), which can be naively interpreted as a uniformly expanding shell. The low incidence of redshifted Balmer absorbers in LRD spectra (e.g., I. Labbe et al. 2024; A. de Graaff et al. 2025a; F. D’Eugenio et al. 2025b, 2026; Y. Ma et al. 2026) can therefore be explained by the requirement of high inclination angles to observe such features (see also A. Sneppen et al. 2026). Such a picture is broadly in line with disk wind models for AGN with broad absorption lines (e.g., P. B. Hall et al. 2002; H. Zhou et al. 2019) and around stars with circumstellar disks (e.g., J. Erkal et al. 2022), such as accreting T Tauri stars (S. Edwards et al. 2006) or cataclysmic variables (D. Proga 2003).\r\n\r\n4.3. Implications of Rotating Winds for the Emission Lines of LRDs\r\nThe disk wind hypothesis would imply that a photosphere in the shape of a rotating disk is the source of the optical continuum emission, and drives winds that can explain the observed absorption trough. Emission lines originating in a thin rotating disk would have a double-peaked profile in the idealized case (for most inclination angles), but this is not necessarily true if the disk is not sufficiently thin (e.g., N. Murray & J. Chiang 1997), for instance, in the case of a puffed-up disk associated with super-Eddington accretion (e.g., H. Liu et al. 2026). In addition, most line emission would not be produced directly at the base of the disk, but slightly outside (e.g., via collisional cooling or residual recombination; A. Torralba et al. 2026), where the rotational velocity is lower, and the dynamics are complex (e.g., G. A. Shields 1977).\r\n\r\nThe Balmer lines of most LRDs are dominated by broad, symmetric exponential components that are associated with broadening by electron scattering (e.g., V. Rusakov et al. 2026; J. Matthee et al. 2026). For PAN-BH*-1, the Hα line profile of PAN-BH*-1 is compatible with a broad exponential profile emerging through a dense wind where the absorption trough is produced. In dense gas with a large column density of neutral hydrogen, and optically thick to Balmer transitions (NHI,2s ≳ 1014 cm−2), resonant scattering effects become important. Crucially, resonant scattering impacts Hα and Hβ differently (e.g., S.-J. Chang et al. 2026), hence the 3D radiative transfer and photon redistribution of both lines may produce different profiles (see, e.g., Figure 2 in D. Proga 2003). Therefore, the empirical fitting and interpretation of the absorption profiles becomes nontrivial. Dedicated radiative transfer modeling is necessary to study such effects, and they can be tested in other emission lines with high optical depth, such as He i λ10830 Å, or resonant lines like C iv λ1550.\r\n\r\n5. Implications for the Galaxy and Black Hole Masses\r\n5.1. Properties of the Host Galaxy\r\nAssuming that the narrow component of Hα corresponds to ISM emission in the host galaxy, we compute the associated star formation rate using the local calibration from R. C. Kennicutt & N. J. Evans (2012) and assuming no dust attenuation. We obtain SFR(Hα) = 3.3 ± 0.3 M⊙ yr−1. A somewhat lower value of SFR(Hα) = 2.1 ± 0.2 M⊙ yr−1 is obtained using the high-redshift (z ≳ 4) calibrations in I. G. Kramarenko et al. (2026), which might be more appropriate for a young dwarf galaxy with a bursty star formation history. The star formation rates are low, but in line with a main-sequence galaxy with (extrapolating the relation from J. S. Speagle et al. 2014). Assuming zero dust attenuation, the UV absolute magnitude (MUV = −16.7 ± 0.7; Section 3.1) would imply SFR(UV) = 0.18 ± 0.12 M⊙ yr−1 (R. C. Kennicutt & N. J. Evans 2012). The discrepancy between the UV and Hα inferred star formation rate suggests there is some amount of dust attenuation in the host galaxy.\r\n\r\nWe derive a dynamical mass from the width of the narrow component Hα line and the estimated UV size as , adopting the empirical virial correction K(n)K(q) from A. van der Wel et al. (2022), where K(n) and K(q) are functions of the best-fit ellipticity and Sérsic index (see Appendix B). Adopting a Mdyn/M* factor of 40 as found by A. de Graaff et al. (2024) for dwarf galaxies at high redshift, we infer a stellar mass of . However, the Mdyn/M* is very uncertain in this regime, and the uncertainty can span over 1 dex (A. Saldana-Lopez et al. 2025). We advise caution in interpreting this result, as there are large uncertainties in the measurements of the narrow Hα component, the HST morphology, and the empirical relations used.\r\n\r\nAs discussed in Section 4, the absorption profile is compatible with broadening by a rotating disk wind, and numerical modeling of such configurations often predicts a narrow component arising from increased transmission due to purely kinematic effects in the wind geometry (D. Proga et al. 2000; D. Proga 2003; D. Proga & T. R. Kallman 2004). This would be an alternative explanation for at least part of the narrow component flux. On the other hand, most LRDs present narrow [O iii] emission that is often associated with the host galaxy. Indeed, the ionized gas producing [O iii] emission should have associated emission in the Hα and higher-order Balmer lines. However, constraining this component largely depends on the assumptions on dust attenuation or ISM conditions, and requires very high S/N and resolution data. Deep, space-based follow-up observations of PAN-BH*-1 would be very constraining for the wind kinematics (e.g., by the joint analysis of Hβ) and to assess whether a narrow component comes from a host galaxy (e.g., by comparing to a narrow Hβ component or [O iii] λλ4960, 5008).\r\n\r\n5.2. Black Hole Mass From Photosphere Models\r\nThe general physical setup of LRDs is an open debate, and their masses are a major unknown. Due to the multiple differences with respect to the classical AGN population, the validity of standard virial calibrations has been questioned (e.g., V. Rusakov et al. 2026; J. E. Greene et al. 2026; A. Sneppen et al. 2026; A. Torralba et al. 2026, although see, e.g., M. Brazzini et al. 2025, 2026; J. Scholtz et al. 2026 for an alternative interpretation).\r\n\r\nOne can obtain a mass estimate assuming a system in radiative equilibrium with Lbol/LEdd = 1 (e.g., H. Umeda et al. 2026); this yields a total mass of ≈106 M⊙, using the bolometric luminosity from integrating the best-fit blackbody in Section 3.1. Recently, H. Liu et al. (2026) developed a synthetic spectral library of LRD atmosphere models. In these models, the density of the photosphere is regulated by the net surface gravity of an optically thick atmosphere, enabling constraints on the mass of the system. We fit the JWST photometry of PAN-BH*-1 using the models from H. Liu et al. (2026), assuming a negligible contribution from a host galaxy to the optical continuum. The best-fit model has effective temperature Teff = 4800 K, surface gravity , and metallicity (; see Figure 1). The best-fit implies a total mass of the system (BH plus gas) of (Equation (6) in H. Liu et al. 2026, assuming hydrostatic equilibrium). For the second and third best fits, we obtain and −2, respectively (, respectively; with the same metallicity and effective temperature), which would imply lower limits to the system mass between and 4. The bolometric luminosity of PAN-BH*-1 (from the integral of the best-fit green curve in Figure 1) implies an Eddington luminosity ratio of L/LEdd ≲ 13, assuming the best-fit mass from the H. Liu et al. (2026) models. The elevated Eddington ratio is in line with the hypothesis of a radiation-driven wind discussed in Section 4, and allows for somewhat larger system masses. The low masses obtained with this model, combined with the stellar mass inferred from dynamical arguments for the host galaxy (Section 3.3) set lower limits to the BH-to-stellar mass ratio of MBH/M* ≳ 10−4–10−2, which are compatible with the relations observed in the Local Universe, within the large uncertainties (A. E. Reines & M. Volonteri 2015).\r\n\r\n6. Conclusions\r\nIn this Letter, we presented the discovery and spectroscopic confirmation of PAN-BH*-1, an LRD with an extreme Balmer break at z = 1.731. The strength of the Balmer break (F115W/F814W = 7 ± 1) is comparable to the most extreme LRDs known, The Cliff (A. de Graaff et al. 2025a) and MoM-BH* (R. P. Naidu et al. 2025). We summarize the observations and our main conclusions as follows.\r\n\r\n\r\n1.  \r\nWe obtained deep VLT/X-Shooter spectroscopy of PAN-BH*-1. The Hα emission line is luminous and broad (LHα = 1043 erg s−1), and has an unusually strong absorption. Hβ is detected with an S/N ≈ 6, and we conservatively estimate a lower limit for the Balmer decrement of Hα/Hβ > 9.4 (at a 3σ confidence level), in line with other LRDs in the literature (e.g., A. de Graaff et al. 2025b; G. P. Nikopoulos et al. 2026).\r\n2.  \r\nThe absorption trough spans from −520 to 267 km s−1 (at a transmission level of 99%). We interpret the presence of blue- and redshifted absorption as produced by a disk wind, analogous to those analyzed in the context of broad absorption line quasars or accreting stars. This hypothesis would imply that the source of the optical continuum is likely a thick photospheric disk.\r\n3.  \r\nWe detect a narrow Hα component (FWHM = 184 ± 12 km s−1), which we interpret as probing a host galaxy with M* ≈ 108 M⊙ and SFR = 2–3 M⊙. This interpretation is in line with the extended rest-NUV morphology measured in the HST bands (\r\n kpc).\r\n4.  \r\nBy fitting the synthetic atmosphere models of H. Liu et al. (2026), we estimate a system mass (BH+envelope) of 104–106 M⊙. The inferred masses, together with the stellar mass inferred from morphology and narrow emission line dynamics, imply BH-to-stellar mass ratios of 10−2–10−4, close to the extrapolated trend in the local Universe (A. E. Reines & M. Volonteri 2015).\r\n5.  \r\nThe confirmation of this source at cosmic noon (magnitude of ≈22 in the K band, Hα flux ≈5 × 10−16 erg s−1 cm−2) proves the feasibility of detecting extreme LRDs at such epochs with wide-area spectroscopic surveys like Euclid or the forthcoming Nancy Grace Roman Space Telescope.\r\n\r\nAcknowledgments\r\nA.T. thanks Debasish Dutta and Tamara Bogdanović for useful conversations about stellar and AGN winds.\r\n\r\nWe thank the scientific referee for the useful and constructive feedback, which helped improve the quality of this paper.\r\n\r\nJ.M. and A.T. acknowledge funding by the European Union (ERC, AGENTS, 101076224). The work of CCW is supported by NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. A.P.C. warmly acknowledges the support of the National Science Foundation through the NSF Graduate Research Fellowship Program. A.d.G. acknowledges support from a Clay Fellowship awarded by the Smithsonian Astrophysical Observatory.\r\n\r\nBased on observations made with ESO Telescopes at the Paranal Observatory under program IDs 116.294D and 116.2AQ0.\r\n\r\nThis work is based in part on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These observations are associated with programs #2514 and #9433. C.C.W. gratefully acknowledges support for program JWST-GO-2514 provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127. The authors acknowledge the team led by co-PIs R. Maiolino and F. D’Eugenio for developing their observing program with a zero-exclusive-access period.\r\n\r\nThis research is based on observations made with the NASA/ESA Hubble Space Telescope obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5–26555. These observations are associated with program #15117.\r\n\r\nThe JWST and HST data presented in this article were obtained from the Mikulski Archive for Space Telescopes (MAST) at the Space Telescope Science Institute. The specific observations analyzed can be accessed via doi:10.17909/ydwx-st06.\r\n\r\nThis work is based in part on observations made with the Spitzer Space Telescope, which was operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. The Spitzer data used in this work can be found in doi:10.26131/IRSA3.\r\n\r\nThis work was supported by the International Space Science Institute (ISSI) in Bern, through ISSI International Team project #25-659 “Little Red Dots, Big Open Questions.”\r\n\r\nJWST cartoon in Figure 6, credit: NASA.\r\n\r\nFacilities: VLT:Kueyen - Very Large Telescope (Kueyen) (X-Shooter), VLT:Yepun (HAWK-I), JWST - James Webb Space Telescope (NIRCam, NIRspec), HST - Hubble Space Telescope satellite (ACS), Spitzer - Spitzer Space Telescope satellite (IRAC, MIPS) - .\r\n\r\nSoftware: astropy (Astropy Collaboration et al. 2013, 2018; Astropy Collaboration et al. 2022), NumPy (C. R. Harris et al. 2020), SciPy (P. Virtanen et al. 2020), pysersic (I. Pasha & T. B. Miller 2023), stpsf (M. D. Perrin et al. 2014), lmfit (M. Newville et al. 2014), EsoRex (ESO CPL Development Team 2015), Claude (used for Python coding; https://claude.ai/), SEP (K. Barbary 2016).","article_number":"L37","volume":1005,"corr_author":"1","publication_status":"published","oa_version":"Published Version","tmp":{"name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","image":"/images/cc_by.png","short":"CC BY (4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode"},"publisher":"IOP Publishing","scopus_import":"1","dataavailabilitystatement":"Based on observations made with ESO Telescopes at the Paranal Observatory under program IDs 116.294D and 116.2AQ0.\r\n\r\nThis work is based in part on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These observations are associated with programs #2514 and #9433. C.C.W. gratefully acknowledges support for program JWST-GO-2514 provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127. The authors acknowledge the team led by co-PIs R. Maiolino and F. D’Eugenio for developing their observing program with a zero-exclusive-access period.\r\n\r\nThis research is based on observations made with the NASA/ESA Hubble Space Telescope obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5–26555. These observations are associated with program #15117.\r\n\r\nThe JWST and HST data presented in this article were obtained from the Mikulski Archive for Space Telescopes (MAST) at the Space Telescope Science Institute. The specific observations analyzed can be accessed via doi:10.17909/ydwx-st06.\r\n\r\nThis work is based in part on observations made with the Spitzer Space Telescope, which was operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. The Spitzer data used in this work can be found in doi:10.26131/IRSA3.\r\n\r\nThis work was supported by the International Space Science Institute (ISSI) in Bern, through ISSI International Team project #25-659 “Little Red Dots, Big Open Questions.”\r\n\r\nJWST cartoon in Figure 6, credit: NASA.\r\n\r\nFacilities: VLT:Kueyen - Very Large Telescope (Kueyen) (X-Shooter), VLT:Yepun (HAWK-I), JWST - James Webb Space Telescope (NIRCam, NIRspec), HST - Hubble Space Telescope satellite (ACS), Spitzer - Spitzer Space Telescope satellite (IRAC, MIPS) - .\r\n\r\nSoftware: astropy (Astropy Collaboration et al. 2013, 2018; Astropy Collaboration et al. 2022), NumPy (C. R. Harris et al. 2020), SciPy (P. Virtanen et al. 2020), pysersic (I. Pasha & T. B. Miller 2023), stpsf (M. D. Perrin et al. 2014), lmfit (M. Newville et al. 2014), EsoRex (ESO CPL Development Team 2015), Claude (used for Python coding; https://claude.ai/), SEP (K. Barbary 2016).","fulldoi":"https://doi.org/10.3847/2041-8213/ae7bfd","DOAJ_listed":"1","type":"journal_article"},{"publisher":"IOP Publishing","tmp":{"name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","image":"/images/cc_by.png","short":"CC BY (4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode"},"scopus_import":"1","dataavailabilitystatement":"The specific observations analyzed can be accessed via doi:10.17909/qk5z-7p30. The scripts used to generate the data and results in this work can be found in Zenodo at doi:10.5281/zenodo.20513668 and GitHub https://github.com/zachlewis99/rubies_mzr","type":"journal_article","DOAJ_listed":"1","fulldoi":"https://doi.org/10.3847/1538-4357/ae7bfc","volume":1005,"article_number":"159","oa_version":"Published Version","publication_status":"published","file":[{"access_level":"open_access","content_type":"application/pdf","date_created":"2026-07-13T07:35:16Z","date_updated":"2026-07-13T07:35:16Z","relation":"main_file","success":1,"file_id":"22273","checksum":"9b13fbbc5e5e921c04676ebc532d9c42","creator":"dernst","file_size":1854628,"file_name":"2026_AstrophysicalJour_Lewis.pdf"}],"doi":"10.3847/1538-4357/ae7bfc","acknowledgement":"This work is based on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These observations are associated with program ID 4233. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under grant No. 2137424 as well as work supported by NASA under Award No. 2025_3-0, issued through the Wisconsin Space Grant Consortium, and JWST-GO-4233. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Aeronautics and Space Administration. Support for program ID 4233 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127. M.V.M. is supported by the National Science Foundation via grant AAG 2205519. A.d.G. acknowledges support from a Clay Fellowship awarded by the Smithsonian Astrophysical Observatory. T.B.M. was supported by a CIERA Fellowship. Part of the computations for this research were performed on the Pennsylvania State University’s Institute for Computational and Data Sciences’ Roar supercomputer. Some/all of the data presented in this article were obtained from the Mikulski Archive for Space Telescopes (MAST) at the Space Telescope Science Institute. The specific observations analyzed can be accessed via doi:10.17909/qk5z-7p30. The scripts used to generate the data and results in this work can be found in Zenodo at doi:10.5281/zenodo.20513668 and GitHub  \r\nhttps://github.com/zachlewis99/rubies_mzr ","quality_controlled":"1","article_processing_charge":"Yes","publication":"The Astrophysical Journal","researchdata_availability":"yes","abstract":[{"lang":"eng","text":"The correlation between galaxy stellar mass and gas-phase metallicity, known as the mass–metallicity relation (MZR), gives key insights into the processes that govern galaxy evolution. However, unquantified observational and selection biases can result in systematic errors in attempts to recover the intrinsic MZR, particularly at higher redshifts. We characterize the MZR at z ∼ 3–6 within a fully Bayesian framework using JWST/NIRSpec spectra of 191 galaxies from the RUBIES survey. We forward model the observed mass–metallicity surface using prospector-generated spectra to account for two selection biases: the survey selection function and the success in observing high signal-to-noise ratio emission lines. We demonstrate that the RUBIES selection function, based on F444W magnitude and F150W – F444W color, has a negligible effect on our measured MZR. A correct treatment of the non-Gaussian metallicity uncertainties from strong-line calibrations lowers the derived MZR normalization by 0.2 dex and flattens the slope by ∼20%; forward modeling the effect of emission line observability steepens the slope by ∼15%. Both of these biases must be taken into account in order to properly measure the intrinsic MZR. This novel forward-modeling process motivates careful consideration of selection functions in future surveys, and paves the way for robust, high-redshift chemical enrichment studies that trace the evolution of the MZR across cosmic time."}],"article_type":"original","OA_place":"publisher","das_tickbox":"1","publication_identifier":{"issn":["0004-637X"],"eissn":["1538-4357"]},"intvolume":"      1005","supplementarymaterial":"no","file_date_updated":"2026-07-13T07:35:16Z","date_updated":"2026-07-13T07:40:41Z","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","ddc":["520"],"date_published":"2026-07-10T00:00:00Z","title":"The mass–metallicity relation and its observational effects at z ∼ 3–6","keyword":["Galaxy evolution","Chemical enrichment","Metallicity","Galaxy abundances","Scaling relations"],"arxiv":1,"language":[{"iso":"eng"}],"_id":"22264","issue":"2","day":"10","PlanS_conform":"1","status":"public","OA_type":"gold","year":"2026","citation":{"chicago":"Lewis, Zach, Michael V. Maseda, Anna De Graaff, Joel Leja, Bingjie Wang, Hans Walter Rix, Ian Mcconachie, et al. “The Mass–Metallicity Relation and Its Observational Effects at z ∼ 3–6.” <i>The Astrophysical Journal</i>. IOP Publishing, 2026. <a href=\"https://doi.org/10.3847/1538-4357/ae7bfc\">https://doi.org/10.3847/1538-4357/ae7bfc</a>.","ista":"Lewis Z, Maseda MV, De Graaff A, Leja J, Wang B, Rix HW, Mcconachie I, Cleri NJ, Bezanson R, Boogaard LA, Brammer G, Greene JE, Hirschmann M, Katz H, Labbé I, Matthee JJ, Miller TB, Naidu RP, Oesch PA, Setton DJ, Suess KA, Weibel A, Whitaker KE, Williams CC. 2026. The mass–metallicity relation and its observational effects at z ∼ 3–6. The Astrophysical Journal. 1005(2), 159.","ieee":"Z. Lewis <i>et al.</i>, “The mass–metallicity relation and its observational effects at z ∼ 3–6,” <i>The Astrophysical Journal</i>, vol. 1005, no. 2. IOP Publishing, 2026.","ama":"Lewis Z, Maseda MV, De Graaff A, et al. The mass–metallicity relation and its observational effects at z ∼ 3–6. <i>The Astrophysical Journal</i>. 2026;1005(2). doi:<a href=\"https://doi.org/10.3847/1538-4357/ae7bfc\">10.3847/1538-4357/ae7bfc</a>","short":"Z. Lewis, M.V. Maseda, A. De Graaff, J. Leja, B. Wang, H.W. Rix, I. Mcconachie, N.J. Cleri, R. Bezanson, L.A. Boogaard, G. Brammer, J.E. Greene, M. Hirschmann, H. Katz, I. Labbé, J.J. Matthee, T.B. Miller, R.P. Naidu, P.A. Oesch, D.J. Setton, K.A. Suess, A. Weibel, K.E. Whitaker, C.C. Williams, The Astrophysical Journal 1005 (2026).","apa":"Lewis, Z., Maseda, M. V., De Graaff, A., Leja, J., Wang, B., Rix, H. W., … Williams, C. C. (2026). The mass–metallicity relation and its observational effects at z ∼ 3–6. <i>The Astrophysical Journal</i>. IOP Publishing. <a href=\"https://doi.org/10.3847/1538-4357/ae7bfc\">https://doi.org/10.3847/1538-4357/ae7bfc</a>","mla":"Lewis, Zach, et al. “The Mass–Metallicity Relation and Its Observational Effects at z ∼ 3–6.” <i>The Astrophysical Journal</i>, vol. 1005, no. 2, 159, IOP Publishing, 2026, doi:<a href=\"https://doi.org/10.3847/1538-4357/ae7bfc\">10.3847/1538-4357/ae7bfc</a>."},"date_created":"2026-07-12T22:02:17Z","department":[{"_id":"JoMa"}],"external_id":{"arxiv":["2512.03134"]},"month":"07","oa":1,"has_accepted_license":"1","author":[{"first_name":"Zach","last_name":"Lewis","full_name":"Lewis, Zach"},{"last_name":"Maseda","first_name":"Michael V.","full_name":"Maseda, Michael V."},{"full_name":"De Graaff, Anna","first_name":"Anna","last_name":"De Graaff"},{"last_name":"Leja","first_name":"Joel","full_name":"Leja, Joel"},{"first_name":"Bingjie","last_name":"Wang","full_name":"Wang, Bingjie"},{"first_name":"Hans Walter","last_name":"Rix","full_name":"Rix, Hans Walter"},{"full_name":"Mcconachie, Ian","last_name":"Mcconachie","first_name":"Ian"},{"full_name":"Cleri, Nikko J.","last_name":"Cleri","first_name":"Nikko J."},{"full_name":"Bezanson, Rachel","first_name":"Rachel","last_name":"Bezanson"},{"full_name":"Boogaard, Leindert A.","first_name":"Leindert A.","last_name":"Boogaard"},{"full_name":"Brammer, Gabriel","last_name":"Brammer","first_name":"Gabriel"},{"full_name":"Greene, Jenny E.","first_name":"Jenny E.","last_name":"Greene"},{"last_name":"Hirschmann","first_name":"Michaela","full_name":"Hirschmann, Michaela"},{"first_name":"Harley","last_name":"Katz","full_name":"Katz, Harley"},{"last_name":"Labbé","first_name":"Ivo","full_name":"Labbé, Ivo"},{"last_name":"Matthee","id":"7439a258-f3c0-11ec-9501-9df22fe06720","first_name":"Jorryt J","full_name":"Matthee, Jorryt J","orcid":"0000-0003-2871-127X"},{"first_name":"Tim B.","last_name":"Miller","full_name":"Miller, Tim B."},{"full_name":"Naidu, Rohan P.","last_name":"Naidu","first_name":"Rohan P."},{"first_name":"Pascal A.","last_name":"Oesch","full_name":"Oesch, Pascal A."},{"full_name":"Setton, David J.","last_name":"Setton","first_name":"David J."},{"last_name":"Suess","first_name":"Katherine A.","full_name":"Suess, Katherine A."},{"first_name":"Andrea","last_name":"Weibel","full_name":"Weibel, Andrea"},{"first_name":"Katherine E.","last_name":"Whitaker","full_name":"Whitaker, Katherine E."},{"last_name":"Williams","first_name":"Christina C.","full_name":"Williams, Christina C."}]},{"article_type":"original","abstract":[{"text":"The detection of strong Balmer breaks and absorption features in Little Red Dots (LRDs) suggests they host active galactic nuclei embedded within dense gas envelopes, potentially powered by super-Eddington accretion. We present GLIMPSE-17775, a luminous (Lbol ∼ 1045 erg s−1) LRD at z = 3.501 behind Abell S1063 (μ ∼ 2), observed with deep JWST/NIRCam and a ∼20 hr (80 hr delensed) NIRSpec G395M spectrum. The data reveal over 40 emission and absorption features, including a rich forest of low-ionization Fe ii lines and numerous broad hydrogen recombination transitions. We use this depth to test the dense-gas interpretation through five independent diagnostics. Nearly all permitted lines show exponential wings with consistent FWHM, a signature of Thomson scattering requiring ne ≳ 108 cm−3. Adopting this width yields MBH ∼ 106.7M⊙, a factor of 10 lower than Gaussian fits, and λEdd ∼ 1.8. Additional diagnostics support the same picture: a pronounced Balmer break (fν,4050/fν,3670 = 2.0 ± 0.1), enhanced He i λ7065 and λ10830 with P-Cygni absorption, Bowen-fluorescent O i λ8446–λ11290 emission requiring Lyβ pumping, and 16 Fe ii lines matching fluorescence models. These features indicate a dense (n ∼ 108 cm−3), partially ionized cocoon where scattering and fluorescence dominate line formation, providing strong evidence that at least some LRDs are powered by super-Eddington black hole growth in the early Universe.","lang":"eng"}],"publication":"The Astrophysical Journal","researchdata_availability":"no","article_processing_charge":"Yes","quality_controlled":"1","acknowledgement":"IOP Science home\r\nThe Astrophysical Journal\r\nThe American Astronomical Society, find out more.\r\n\r\nThe following article isOpen access\r\nThe Deepest GLIMPSE of a Dense Gas Cocoon Enshrouding a Little Red Dot\r\nVasily Kokorev, John Chisholm, Rohan P. Naidu, Seiji Fujimoto, Hakim Atek, Gabriel Brammer, Steven L. Finkelstein, Hollis B. Akins, Danielle A. Berg, Lukas J. FurtakShow full author list\r\n\r\nPublished 2026 June 10 • © 2026. The Author(s). Published by the American Astronomical Society.\r\nThe Astrophysical Journal, Volume 1004, Number 2\r\nCitation Vasily Kokorev et al 2026 ApJ 1004 153\r\nDOI 10.3847/1538-4357/ae4ed7\r\n\r\nPDFOpens in a new tab.ePub\r\nAuthors\r\nFigures\r\nTables\r\nReferences\r\nArticle data\r\nPDFOpens in a new tab.ePub\r\nArticle metrics\r\n5138 Total downloads\r\n\r\n22 total citations on Dimensions.\r\nShare this article\r\nArticle information\r\nAbstract\r\nThe detection of strong Balmer breaks and absorption features in Little Red Dots (LRDs) suggests they host active galactic nuclei embedded within dense gas envelopes, potentially powered by super-Eddington accretion. We present GLIMPSE-17775, a luminous (Lbol ∼ 1045 erg s−1) LRD at z = 3.501 behind Abell S1063 (μ ∼ 2), observed with deep JWST/NIRCam and a ∼20 hr (80 hr delensed) NIRSpec G395M spectrum. The data reveal over 40 emission and absorption features, including a rich forest of low-ionization Fe ii lines and numerous broad hydrogen recombination transitions. We use this depth to test the dense-gas interpretation through five independent diagnostics. Nearly all permitted lines show exponential wings with consistent FWHM, a signature of Thomson scattering requiring ne ≳ 108 cm−3. Adopting this width yields MBH ∼ 106.7M⊙, a factor of 10 lower than Gaussian fits, and λEdd ∼ 1.8. Additional diagnostics support the same picture: a pronounced Balmer break (fν,4050/fν,3670 = 2.0 ± 0.1), enhanced He i λ7065 and λ10830 with P-Cygni absorption, Bowen-fluorescent O i λ8446–λ11290 emission requiring Lyβ pumping, and 16 Fe ii lines matching fluorescence models. These features indicate a dense (n ∼ 108 cm−3), partially ionized cocoon where scattering and fluorescence dominate line formation, providing strong evidence that at least some LRDs are powered by super-Eddington black hole growth in the early Universe.\r\n\r\nExport citation and abstract\r\nBibTeXRIS\r\n\r\nPrevious article in issue\r\nNext article in issue\r\nRelated links\r\n\r\nOriginal content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.\r\n\r\n1. Introduction\r\nOne of the most enticing puzzles brought about by the launch of the James Webb Space Telescope (JWST) has been the discovery of red, compact objects called “Little Red Dots” (LRDs; J. Matthee et al. 2024). Previously invisible to the Hubble Space Telescope (HST) due to their extreme faintness in the optical and lack of near-infrared (NIR) coverage, LRDs have emerged in abundance (V. Kokorev et al. 2024a; H. B. Akins et al. 2025a; D. D. Kocevski et al. 2025; G. Barro et al. 2026) thanks to the unprecedented NIR sensitivity of JWST.\r\n\r\nTheir unusual properties—such as compact morphologies in rest-optical and distinctive “V-shaped” spectral energy distributions (SEDs)—make LRDs easy to identify in JWST fields; however, this is where the simplicity ends. Explaining LRDs as either evolved or dusty compact galaxies proves difficult: The former scenario requires massive stellar populations that strain Lambda cold dark matter (ΛCDM) predictions (M. Boylan-Kolchin 2023; I. Labbé et al. 2023), while the latter implies significant dust emission, yet none is observed (C. M. Casey et al. 2024; G. C. K. Leung et al. 2025; H. B. Akins et al. 2025a; I. Labbé et al. 2025).\r\n\r\nOver time, the accumulating detections of broad Balmer-series emission lines (D. D. Kocevski et al. 2023, 2025; J. Matthee et al. 2024, just to name a few), often accompanied by signatures of extreme ionization (e.g., V. Kokorev et al. 2023), have begun to clarify the physical origin of LRDs, pointing increasingly toward active galactic nuclei (AGN) as the underlying power source. In parallel, the much needed advent of NIRSpec Micro Shutter Assembly (MSA) programs based on red targets selected from JWST imaging (e.g., A. de Graaff et al. 2025b) has provided critical confirmation: Nearly all point sources exhibiting “V-shaped” SEDs reveal broad emission lines upon spectroscopic follow-up (R. E. Hviding et al. 2025), solidifying their AGN interpretation.\r\n\r\nThe nature of the spectral inflection point in LRDs, typically located near ∼3600 Å, has also undergone significant revision. Initially interpreted as a stellar Balmer break (I. Labbé et al. 2023), this feature implied implausibly high stellar masses (M*) far too early in cosmic history (M. Boylan-Kolchin 2023; N. Sabti et al. 2024). A second hypothesis invoked differential dust attenuation and host-galaxy contamination in the rest-UV to explain the sharp discontinuity (M. Volonteri et al. 2025). However, this explanation was soon ruled out by D. J. Setton et al. (2025) and Y. Ma et al. (2025), who demonstrated that the break generally lies around the Balmer limit, albeit with a fundamentally different origin than initially proposed.\r\n\r\nMore recently, a series of theoretical and observational works have converged on a new picture in which LRDs may host accreting black holes enshrouded in exceptionally dense, partially ionized gas cocoons, often referred to as “black hole stars” (hereafter BH*; A. de Graaff et al. 2025b; K. Inayoshi & R. Maiolino 2025; R. P. Naidu et al. 2025; A. J. Taylor et al. 2025). Here, BH* is used in an empirical sense to denote cocooned black holes whose emergent spectra exhibit a combination of black-hole-like and star-like features, such as broad permitted lines, steep Balmer-limit breaks, and Balmer absorption, as observed in the archetypal BH* sources (A. de Graaff et al. 2025b; R. P. Naidu et al. 2025). This usage does not assume a specific geometry or formation channel: The underlying physical picture involves an AGN power-law ionizing spectrum processed through very dense gas, and similar phenomenology can arise in a range of dense-gas configurations (e.g., K. Inayoshi & R. Maiolino 2025; D. Kido et al. 2025; H. Liu et al. 2025; A. Sneppen et al. 2026). In such environments, suppressed X-ray and radio emission (e.g., K. Inayoshi & R. Maiolino 2025; R. P. Naidu et al. 2025) arise naturally from the high optical depth, while the UV emission and forbidden optical lines (e.g., [O iii] λλ4959, 5007) may originate in the more extended host (e.g., A. de Graaff et al. 2025d).\r\n\r\nThe dense-gas interpretation also offers a natural explanation for the P-Cygni-like Balmer and helium profiles frequently seen in high-signal-to-noise-ratio (S/N) spectra (J. Matthee et al. 2024), the non-Gaussian, exponentially winged line shapes predicted by radiative-transfer models of scattering in ionized gas (S.-J. Chang et al. 2026; V. Rusakov et al. 2026), and Lyα-like resonantly scattered shapes (R. P. Naidu et al. 2025; S.-J. Chang et al. 2026). Intriguingly, if electron and resonant scattering indeed dominate the broad-line widths, then the true virial velocities (traced by intrinsically narrower Gaussian cores)—and hence black hole masses—could be lower by an order of magnitude, alleviating the apparent tension between LRD black hole masses and their compact host galaxies (V. Rusakov et al. 2026).\r\n\r\nSo far, however, the BH*/dense-gas interpretation of LRDs has relied largely on the Balmer break, occasional absorption features (X. Lin et al. 2026), and, to a limited extent, the shapes of broad emission lines (V. Rusakov et al. 2026). While these features are consistent with the presence of dense, partially ionized gas, they stop short of providing direct spectroscopic confirmation of the physical conditions expected by the BH* scenario. What has been missing is an unambiguous demonstration—through emission-line physics—that LRDs indeed host dense, optically thick cocoons surrounding rapidly accreting black holes. Such evidence would directly tie the observed line formation, excitation, and radiative transfer to dense, stratified envelopes of gas surrounding the central engine.\r\n\r\nIn this work, we present precisely such a case: an exceptionally deep, ∼20 hr (equivalent to 80 hr without lensing magnification) JWST/NIRSpec G395M spectrum of a luminous LRD at z = 3.50102. The target, GLIMPSE-17775, lies in a highly magnified region of the massive galaxy cluster Abell S1063 (hereafter AS1063) and benefits from the combined power of JWST/NIRCam imaging from the GLIMPSE GO program (PID 3293; PIs: H. Atek & J. Chisholm) and recent NIRSpec spectroscopy from the GLIMPSEDirector's Discretionary Time (DDT) (hereafter GLIMPSE-D) program (PID 9223; PIs: S. Fujimoto & R. Naidu). This synergy of ultradeep spectroscopy and strong gravitational lensing enables an unprecedented view of GLIMPSE-17775, revealing rest-frame optical and NIR features at a level unseen before in any LRD. We detect over 40 emission and absorption features, including 16 Fe ii transitions that form a dense “iron forest.” The remarkable richness of this spectrum makes GLIMPSE-17775 a uniquely powerful laboratory for dissecting the dense, radiation-dominated environments that accompany early black hole growth.\r\n\r\nThis paper is organized as follows. In Section 2, we present the GLIMPSE-D NIRSpec dataset alongside the photometric datasets used in this study. In Section 3, we calculate the spectroscopic redshift, describe the identification of prominent emission/absorption features, and describe bespoke fitting of various line complexes. Section 4 describes the measurement of the source morphology, dust attenuation, and black hole masses. In Section 5, we comment on the various properties of the emission features in the our target. Finally, we discuss our findings in Section 6.\r\n\r\nThroughout this work, we assume a flat ΛCDM cosmology with Ωm,0 = 0.3, ΩΛ,0 = 0.7, and H0 = 70 km s−1 Mpc−1, and a G. Chabrier (2003) initial mass function between 0.1 and 100M⊙. All magnitudes are expressed in the AB system (J. B. Oke 1974).\r\n\r\n2. Observations and Data\r\nThe target, GLIMPSE-17775, was originally identified as a bright LRD candidate in JWST/NIRCam imaging captured by the GLIMPSE (PID: 3293; PIs: H. Atek & J. Chisholm) survey (H. Atek et al. 2025) of the lensed AS1063 Hubble Frontier Field (HFF; J. M. Lotz et al. 2017). The highly magnified area of AS1063 has already successfully yielded z  >  16 galaxy candidates (V. Kokorev et al. 2025), potential Population III (Pop III) hosts (S. Fujimoto et al. 2025a), numerous faint and high-redshift galaxies (I. Chemerynska et al. 2026), new constraints on reionization (D. Korber et al. 2025), identification of intermediate-mass black holes (Q. Fei et al. 2025), and a wide variety of enigmatic LRDs, some moderately lensed. The LRD selection was based on the standard compactness plus “V-shape” criteria already laid out in J. E. Greene et al. (2024), V. Kokorev et al. (2024a), H. B. Akins et al. (2025a), and I. Labbé et al. (2025) using photometric redshifts derived with eazy (G. B. Brammer et al. 2008), a technique that has proven successful at consistently identifying many exciting sources (see, e.g., H. B. Akins et al. 2025b; A. de Graaff et al. 2025b; V. Kokorev et al. 2023; R. P. Naidu et al. 2025; A. J. Taylor et al. 2025). Located at zphot = 4.2 ± 0.1, GLIMPSE-17775 stood out in particular due to its extreme rest-optical brightness with mf444w ∼ 23.6 mag and a modest lensing magnification μ ∼ 2. While very little could be done with photometry alone, this marked GLIMPSE-17775 as a promising target for any future spectroscopic follow-up.\r\n\r\n2.1. Photometry\r\nWe use photometry both to select targets for the GLIMPSE-D NIRSpec observations and, during spectroscopic modeling, to constrain the overall shape of the SED and correct for NIRSpec slit losses. In addition to JWST/NIRCam data, we incorporate deep HST Advanced Camera for Surveys and Wide Field Camera 3 imaging from the HFF (J. M. Lotz et al. 2017) and BUFFALO (C. L. Steinhardt et al. 2020) programs. Our reprocessed HST mosaics are based on Gaia-aligned images from the CHArGE archive (V. Kokorev et al. 2022), hosted on the Dawn JWST Archive (F. Valentino et al. 2023). More descriptions of the image reduction and source extraction procedure can be found in R. Endsley et al. (2025), as well as in the GLIMPSE overview paper (H. Atek et al. 2025); we briefly summarize the latter procedure below.\r\n\r\nPhotometry is performed on point-spread function (PSF)-homogenized HST and JWST images, convolved to the resolution of the F480M filter. Source detection is carried out using SExtractor (E. Bertin & S. Arnouts 1996) through two parallel steps. We construct two inverse-variance-weighted detection images: one from the short-wavelength (SW; F090W, F115W, F150W, F200W) bands to preserve spatial resolution, and one from the long-wavelength (LW; F277W, F356W, F444W) bands to ensure sensitivity to red or dusty sources (e.g., LRDs). Unlike the science images, these have not been PSF-matched. These SW and LW detection catalogs are subsequently merged into a single, combined catalog. Photometry is then measured using photutils (L. Bradley et al. 2020) in a range of circular apertures (–). Photometric uncertainties are estimated by placing random apertures in empty regions around each source. Unless stated otherwise, we adopt total fluxes measured within a aperture throughout this work.\r\n\r\n2.2. NIRSpec Observations\r\nGLIMPSE-D NIRSpec data were obtained during a campaign (DDT #9223; PIs: S. Fujimoto & R. Naidu) to study a promising Pop III galaxy candidate (S. Fujimoto et al. 2025a). GLIMPSE-D obtained a total of three G395M/F295LP MSA pointings, totaling 29.78 hr of total exposure time. The pointing center differed for each of the three configurations to maximize the total object yield. In total, the GLIMPSE-D sample contains 384 spectra, with depths varying from 9.2 hr to ∼30 hr. All of the planned observations were successfully executed between 2025 June 30 and July 2. For each MSA configuration, GLIMPSE-D employed a standard three-point nod pattern at an aperture position angle PA_V3 = 2705, using 494 groups per integration with the NRSIRS2 readout mode. The full details of the target selection, prioritization, and MSA planning will be presented in a forthcoming survey paper (S. Fujimoto et al. 2025b).\r\n\r\n2.3. G395M Data Reduction and Calibration\r\nThe GLIMPSE-D MSA spectra were uniformly reduced using msaexp (v0.9.8; G. Brammer 2022). This procedure starts with the level-2 calibrated products obtained from MAST and applies a number of corrections that include 1/f noise, artifact detection and removal, and a bias correction in individual exposures (see J. Rigby et al. 2023 for more details). Together with the JWST pipeline, msaexp sets the slit World Coordinate System, performs flat-fielding, and computes an initial pass-loss correction. Each one of the two-dimensional shutters is then drizzled onto a common pixel grid. Using the standard approach, the background subtraction is performed locally using stacked, source-free shutters. The one-dimensional spectra are then obtained via the optimal extraction method (e.g., P. Arrabal Haro et al. 2023; A. de Graaff et al. 2024), in which the center and width of the extraction “aperture” vary depending on the best-fit Gaussian model (K. Horne 1986), similar to the methodology widely adopted by a variety of other works (e.g., B. Wang et al. 2023; J. E. Greene et al. 2024; V. Kokorev et al. 2024b).\r\n\r\nThe absolute flux calibration of MSA spectra can be influenced by several factors, including the position of the source within the shutter, calibration and astrometric uncertainties, and the intrinsic morphology of the source. To correct for these effects and derive an overall slit-loss correction, we rescale the extracted one-dimensional spectra by convolving them with all available NIRCam filters and comparing the resulting flux densities to the total photometry from the GLIMPSE catalog. A wavelength-dependent correction is then obtained by fitting a second-order polynomial to these differences.\r\n\r\nThe target in this paper was observed in all three configurations; however, one was severely contaminated by sources in the same row, making the data recovery for that configuration unfeasible. Despite this, GLIMPSE-17775 is securely detected in two configurations (33,262 s and 40,703 s), yielding a total integration time of 20.55 hr. We combine the extracted and separately calibrated one-dimensional spectra using inverse-variance weighting. The stacked spectrum is shown in Figure 1. We also make the spectrum publicly available.17\r\n\r\nZoom InZoom OutReset image size\r\nFigure 1. Top: JWST/NIRCam and HST 20 stamps and red, green, blue short-wavelength (SW) and long-wavelength (LW) color images, comprising the F115W, F150W, and F200W and F277W, F356W, and F444W bands, respectively. MSA shutters for both configurations covering GLIMPSE-17775 are shown in blue and red, respectively. The source morphology is resolved and extended up to ∼2 μm, and then appears to transition to a more PSF-dominated and compact shape, echoing a growing sample of LRDs with extended rest-UV morphology (I. Juodžbalis et al. 2024; I. Labbe et al. 2024; J. Matthee et al. 2024; P. Rinaldi et al. 2025a). This likely hints at the presence of the host galaxy in the filters covering the rest-UV. In each panel, we show the total AB magnitude as presented in the GLIMPSE catalog (H. Atek et al. 2025; V. Kokorev et al. 2025). The source is exceptionally bright (M444 ∼ 23.6) and is detected in most JWST bands at >100σ. Middle: two-dimensional MSA G395M spectra covering GLIMPSE-17775. Bottom: combined one-dimensional spectrum (see, e.g., V. Kokorev et al. 2023; A. de Graaff et al. 2025a for the extraction method) of the LRD in the observed frame. We show the data in black, and the uncertainty as a black shaded region. Fixing the systemic redshift to the [S iii] λ9071 line (zspec = 3.50102 ± 0.00019), we show the positions and label the prominent emission with significant (≥3σ) detections as solid vertical lines. Iron lines are shown separately in green. Due to the sheer number of features, not all could be labeled; we therefore display all features in Figure 2. Emission lines for which only upper limits are obtained are shown with dashed lines.\r\n\r\nDownload figure:\r\n\r\nStandard imageHigh-resolution image\r\n3. Emission-line Analysis\r\n3.1. Spectroscopic Redshift\r\nThe spectrum of GLIMPSE-17775 reveals a remarkably wide variety of significantly detected emission and absorption lines. Before focusing on individual features and their complex components, we perform an initial tally of all detectable lines using a heavily modified version of msaexp (G. Brammer 2022; V. Kokorev et al. 2024b). The key modifications allow varying the line widths and fitting multiple components, albeit tied to the same redshift.\r\n\r\nWe fit the full spectrum using msaexp, adopting Gaussian profiles for emission lines and a three-segment cubic spline to model the continuum. This minimal spline structure, appropriate given the high average S/N of GLIMPSE-17775 (≳30), helps prevent overfitting, particularly of features that may be slightly offset in wavelength or velocity space from the average redshift. Emission-line positions are fixed; narrow components are allowed a FWHM between 150 and 800 km s−1, and permitted transitions may include a broad component (800–5000 km s−1).\r\n\r\nThis yields a redshift of zspec = 3.5010 ± 0.0001 (see Table 1). However, several strong lines exhibit significant pixel-level offsets of 100–200 km s−1 relative to this value. These discrepancies are statistically robust and appear in both stacked and individual spectra, suggesting that the derived redshift reflects a weighted average dominated by high-S/N lines. To properly assess velocity structure, a consistent systemic redshift is required. In the following sections describing the detailed line analysis, we adopt the centroid of a narrow forbidden line as the systemic reference frame (specifically [S iii] λ9071; see Section 3.3).\r\n\r\nUsing the updated redshift alongside the strong-lensing model of AS1063 (A. Zitrin et al. 2015; L. Furtak et al. 2026, in preparation), we recalculate the lensing magnification to be μ = 2.04 ± 0.21, consistent with previous estimates based on zphot. With redshift and magnification now fixed, we turn to a deeper analysis of the emission-line properties.\r\n\r\n3.2. Line Identification\r\nBeyond velocity offsets, the initial msaexp fit highlights several notable features. Broad hydrogen lines, ubiquitous in LRDs (e.g., D. D. Kocevski et al. 2023; V. Kokorev et al. 2023; L. J. Furtak et al. 2024; J. Matthee et al. 2024; A. de Graaff et al. 2025b; R. E. Hviding et al. 2025; R. P. Naidu et al. 2025; A. J. Taylor et al. 2025), are strongly favored across the Balmer and Paschen series, with Δχ2 > 10. These include Hα and Pa10 through Paγ. Although Paβ falls near the edge of the detector, we nonetheless observe a prominent broad wing at its expected location (see Figure 1).\r\n\r\nBroad components are also detected in several helium and oxygen lines: He i λ6680, He i λ7065, O i λ8448, He i λ10830, and O i λ11290. Notably, the He i λ10830 line shows a classic P-Cygni profile with a clear blueshifted absorption trough. While Balmer absorption is becoming a familiar sight in LRDs (R. Maiolino et al. 2024; J. Matthee et al. 2024; A. de Graaff et al. 2025b; D. D. Kocevski et al. 2025; R. P. Naidu et al. 2025), helium absorption remains rare, with only a few published cases at high z (e.g., I. Juodžbalis et al. 2024; R. P. Naidu et al. 2024; B. Wang et al. 2025). Curiously, this was also recently reported in local analogs of LRDs (X. Lin et al. 2026).\r\n\r\nThe most striking feature is the detection of an extensive Fe ii emission forest in the rest-NIR—at least 16 distinct features are identified by msaexp and highlighted in green in Figure 1. Previous detections of permitted Fe ii in LRDs have been mostly limited to rest-UV/optical wavelengths using low-resolution PRISM spectra (R. Tripodi et al. 2025), with only few examples in the NIR (e.g., see broad Fe iiλ9200 I. Labbe et al. 2024). Iron has also been identified in local LRD analogs (X. Lin et al. 2026; X. Ji et al. 2026). Only recently have a few Fe ii emitters been reported in medium-resolution (F. D’Eugenio et al. 2025) and high-resolution spectra (A. Torralba et al. 2026). The richness of these lines in GLIMPSE-17775 hints at a dense, partially shielded gas phase, where processes such as Lyβ fluorescence and continuum pumping may be enhancing Fe ii emission (T. A. A. Sigut & A. K. Pradhan 1998, 2003; T. A. A. Sigut et al. 2004), offering a new diagnostic window into early AGN environments.\r\n\r\nIn summary, GLIMPSE-17775 exhibits an exceptionally rich and kinematically complex array of emission and absorption features. While the initial msaexp modeling provides a solid foundation for redshift estimation and line identification, it lacks the flexibility to capture the full diversity of line profiles in this high-S/N dataset. In the following sections, we peel back the spectral layers with increasing precision.\r\n\r\n3.3. Line Fitting\r\nThe exceptional depth of the G395M spectrum for GLIMPSE-17775 enables detailed modeling of both multiple kinematic components and potential velocity offsets between line species. Unless noted otherwise, each line is fit with a single Gaussian narrow component (FWHM = 100−800 km s−1). For permitted lines flagged by msaexp as potentially broad, we follow the approach of V. Rusakov et al. (2026) and model the profile as an intrinsic Gaussian core broadened by electron scattering, implemented via convolution with an exponential-wing component. The intrinsic Gaussian FWHM is allowed to vary between 500 and 5000 km s−1. The characteristic scattering width (i.e., the strength of the exponential wings, W) is treated as a free parameter and is allowed to vary independently between different transitions. For each broad line, we also perform an alternative fit with the W parameter fixed to zero (pure Gaussian) and compare the resulting goodness of fit to assess whether the exponential wings are statistically required. Line centers are allowed to vary independently unless otherwise specified.\r\n\r\nAbsorption lines are modeled using a Gaussian optical-depth profile, where the observed flux is Fobs = Fem e−τ(λ), where . The free parameters are then the central optical depth τ0, velocity width Δvabs, and redshift zabs (see I. Juodžbalis et al. 2024). Widths and redshifts (for both narrow and broad components) are typically free, with redshift limited to ± 0.1 from the msaexp value. Local continua are fit using first-order polynomials.\r\n\r\nAll individual model components are first initialized and coadded on an oversampled wavelength grid. To take into account the wavelength-dependent resolution of the grating, we interpolate our model onto a variable step grid while making sure that the total integrated flux is preserved. Further, we increase the nominal spectral resolution by a factor of 1.7, as it has been shown that the spectral resolution for a pointlike source falling within a shutter is higher than that of a uniformly illuminated slitlet (A. de Graaff et al. 2024). Fitting uses nonlinear χ2 minimization, with uncertainties derived from multivariate resampling of the covariance matrix.\r\n\r\nTable 1. Source Properties\r\n\r\nParametera\tGLIMPSE-17775\r\nID\t17775\r\nR.A. [deg]\t342.20080\r\nDecl. [deg]\t–44.54366\r\nzphot (eazy)\t4.2 ± 0.1\r\nzspec ([S iii] λ9071)\t3.50102 ± 0.00019\r\nμ\t2.04 ± 0.21\r\nMUV [AB mag]\t−17.27 ± 0.05\r\nreff,UV [pc]\t1000 ± 200\r\nreff,opt [pc]\t<300\r\nβ\t–0.69 ± 0.12\r\nlog10(MBH/M⊙)\t6.65 ± 0.15\r\nLbol [erg s−1]\t(1.06 ± 0.14)×1045\r\nλedd\t1.86 ± 0.25\r\nlog10(M*/M⊙)\t<7.5\r\nAV\t0.1 ± 0.3\r\nfν,4050Å/fν,3670Å\t2.02 ± 0.10\r\nNote. aPhysical parameters are corrected for the lensing magnification.\r\n\r\nDownload table as: \r\nASCIITypeset image\r\n\r\nGiven the complexity, the spectrum is divided into six windows grouped by line species or proximity (see Figure 2). Below, we describe the assumptions adopted for each window. Final fluxes and equivalent widths of the narrow and broad lines are listed in Tables 2 and 3, respectively, while kinematics are reported in Tables 4 and 5. We show detailed line fits in Figure 2.\r\n\r\nZoom InZoom OutReset image size\r\nFigure 2. A staggering abundance of spectral lines in GLIMPSE-17775 at z = 3.501. For each spectral window defined in Section 3.3, we show the data (black), the best-fit narrow and broad components (dark purple and blue), and the total best-fit model including the continuum (red). All broad components were fit with models allowing exponential wings. The ΔBIC between exponential and Gaussian fits is reported in the top right of each panel; negative values indicate a preference for an exponential profile. The lower panels display the uncertainty-weighted residuals for each fit.\r\n\r\nDownload figure:\r\n\r\nStandard imageHigh-resolution image\r\nTable 2. Fluxes of Narrow Emission Lines and Their Rest-frame Equivalent Widthsa\r\n\r\nLine\tλrest\tFlux\tEW0\r\n \t(Å)\t(10−20 erg s−1 cm−2)\t(Å)\r\nNarrow Emission Lines\r\nO i\t6302.0\t54.0 ± 21.2\t3.3 ± 1.2\r\n[N ii]\t6549.0\t25.6 ± 10.3\t1.6 ± 0.7\r\nHα\t6562.8\t2622.9 ± 200.7\t167.7 ± 12.8\r\n[N ii]\t6584.0\t77.1 ± 37.1\t4.9 ± 1.6\r\nHe i\t6680.0\t14.7 ± 11.1\t0.8 ± 0.7\r\n[S ii]\t6717.0\t22.2 ± 0.1\t1.5 ± 0.7\r\n[S ii]\t6731.0\t21.4 ± 0.1\t1.4 ± 0.5\r\nHe i\t7065.0\t461.7 ± 210.2\t31.0 ± 12.2\r\n[Ar iii]\t7138.0\t12.6 ± 3.4\t1.0 ± 0.3\r\nFe ii\t7156.0\t26.2 ± 7.2\t1.8 ± 0.2\r\n[O ii]\t7323.0\t26.0 ± 23.0\t1.7 ± 1.5\r\n[O ii]\t7325.0\t16.9 ± 1.8\t1.2 ± 0.1\r\n[O ii]\t7332.0\t26.2 ± 9.1\t1.8 ± 0.6\r\nFe ii\t8228.0\t23.7 ± 4.2\t2.0 ± 0.3\r\nFe ii\t8239.0\t7.2 ± 4.0\t0.6 ± 0.3\r\nFe ii\t8289.0\t6.3 ± 3.7\t0.5 ± 0.3\r\nFe iii\t8306.0\t5.7 ± 3.6\t0.5 ± 0.3\r\nO i\t8448.0\t67.6 ± 2.4\t6.1 ± 1.3\r\nFe ii\t8470.0\t16.2 ± 5.0\t1.4 ± 0.4\r\nFe ii\t8490.0\t26.7 ± 4.3\t2.4 ± 0.4\r\nPa10\t9015.0\t16.5 ± 5.0\t1.8 ± 0.5\r\n[S iii]\t9071.0\t27.2 ± 2.3\t3.5 ± 0.3\r\nFe ii\t9075.0\t30.0 ± 4.7\t3.4 ± 0.5\r\nFe ii\t9125.0\t16.8 ± 5.2\t1.9 ± 0.6\r\nFe ii\t9134.0\t36.9 ± 5.0\t4.1 ± 0.6\r\nFe ii\t9179.0\t95.0 ± 5.5\t10.6 ± 0.6\r\nFe ii\t9204.0\t50.1 ± 6.1\t5.6 ± 0.7\r\nPa9\t9229.0\t19.4 ± 7.0\t2.2 ± 0.8\r\nFe ii\t9394.0\t17.3 ± 3.9\t2.0 ± 0.5\r\n[S iii]\t9533.0\t84.7 ± 5.9\t10.2 ± 0.7\r\nPa8\t9545.0\t44.8 ± 11.3\t5.4 ± 1.4\r\nFe ii\t9997.0\t29.5 ± 4.5\t3.8 ± 0.6\r\nPaδ\t10049.0\t104.2 ± 12.2\t13.7 ± 1.7\r\nFe ii\t10490.0\t8.0 ± 2.7\t1.1 ± 0.4\r\nFe ii\t10501.0\t24.4 ± 5.9\t3.1 ± 0.8\r\nHe i\t10830.0\t163.0 ± 96.0\t22.6 ± 13.3\r\nPaγ\t10938.0\t146.3 ± 25.5\t20.9 ± 3.8\r\nFe ii\t11128.0\t12.3 ± 3.7\t1.8 ± 0.6\r\nO i\t11290.0\t49.2 ± 4.1\t7.7 ± 2.3\r\nNote. aNot corrected for lensing magnification.\r\n\r\nDownload table as: \r\nASCIITypeset image\r\n\r\nTable 3. Fluxes of Broad Emission Lines and Their Rest-frame Equivalent Widthsa\r\n\r\nLine\tλrest\tFlux\tEW0\r\n \t(Å)\t(10−20 erg s−1 cm−2)\t(Å)\r\nBroad Emission Lines\r\nHα\t6562.8\t14803.5 ± 198.6\t946.3 ± 15.6\r\nHe i\t6680.0\t144.6 ± 44.7\t9.4 ± 2.9\r\nHe i\t7065.0\t824.2 ± 210.0\t55.4 ± 15.1\r\nPa10\t9015.0\t53.7 ± 11.1\t5.8 ± 1.3\r\nPa9\t9229.0\t119.0 ± 13.5\t13.6 ± 1.5\r\nPa8\t9545.0\t191.2 ± 17.0\t23.1 ± 2.1\r\nPaδ\t10049.0\t370.6 ± 15.0\t48.8 ± 2.3\r\nHe i\t10830.0\t2294.9 ± 212.6\t318.8 ± 30.3\r\nPaγ\t10938.0\t652.3 ± 14.0\t92.9 ± 2.4\r\nO i\t8448.0\t93.7 ± 7.9\t8.4 ± 0.7\r\nO i\t11290.0\t106.2 ± 63.9\t16.6 ± 10.4\r\nNote. aNot corrected for lensing magnification.\r\n\r\nDownload table as: \r\nASCIITypeset image\r\n\r\nTable 4. Kinematic Properties of Narrow Lines\r\n\r\nLine\tλrest\tFWHM\tΔv\r\n \t(Å)\t(km s−1)\t(km s−1)\r\nNarrow Emission Lines\r\n[O i]\t6300.3\t455 ± 175\t−101 ± 81\r\nHα\t6562.8\t304 ± 8\t+145 ± 13\r\n[N ii]\t6583.4\t347 ± 117\t+84 ± 47\r\n[S ii]\t6716.4\t232 ± 62\t+82 ± 33\r\n[S ii]\t6731\t232 ± 62\t+82 ± 33\r\nHe i\t6678.2\t87 ± 14\t+40 ± 14\r\nHe i\t7065.2\t408 ± 644\t+112 ± 396\r\n[Ar iii]\t7135.8\t89 ± 50\t−26 ± 20\r\nFe ii\t7155.2\t96 ± 50\t+15 ± 15\r\n[O ii]\t7320.0\t400 ± 120\t−37 ± 72\r\nFe ii\t8228.0\t290 ± 48\t+21 ± 5\r\nFe ii\t8239.0\t290 ± 48\t+21 ± 5\r\nFe ii\t8289.0\t290 ± 48\t+21 ± 5\r\nFe iii\t8306.0\t290 ± 48\t+21 ± 5\r\nO i\t8446.4\t235 ± 30\t−43 ± 19\r\nFe ii\t8470.0\t290 ± 48\t+21 ± 5\r\nFe ii\t8490.0\t290 ± 48\t+21 ± 5\r\nPa10\t9014.9\t259 ± 36\t−46 ± 19\r\n[S iii]\t9071.0\t230 ± 13\t⋯\r\nFe ii\t9075.0\t486 ± 24\t−21 ± 17\r\nFe ii\t9125.0\t486 ± 24\t−21 ± 17\r\nFe ii\t9134.0\t486 ± 24\t−21 ± 17\r\nFe ii\t9179.0\t486 ± 24\t−21 ± 17\r\nFe ii\t9204.0\t486 ± 24\t−21 ± 17\r\nPa9\t9229.0\t259 ± 35\t−46 ± 19\r\nFe ii\t9394.0\t486 ± 24\t−21 ± 17\r\nPa8\t9545.6\t259 ± 36\t−46 ± 19\r\n[S iii]\t9533\t230 ± 13\t+23 ± 13\r\nFe ii\t9997.0\t331 ± 55\t+90 ± 25\r\nPaδ\t10049.4\t332 ± 22\t+21 ± 15\r\nHe i\t10830.3\t287 ± 46\t+112 ± 26\r\nPaγ\t10938.1\t267 ± 25\t+26 ± 17\r\nFe ii\t10490.0\t332 ± 96\t+44 ± 43\r\nFe ii\t10501.0\t332 ± 96\t+44 ± 43\r\nFe ii\t11128.0\t153 ± 116\t+37 ± 30\r\nO i\t11290.0\t260 ± 58\t−33 ± 24\r\nNote. Velocity offsets (Δv) calculated relative to [S iii] λ9071 at z = 3.50102.\r\n\r\nDownload table as: \r\nASCIITypeset image\r\n\r\nTable 5. Kinematic Properties of Broad and Absorption Lines\r\n\r\nLine\tλrest\tFWHM\tW\tΔv\r\n \t(Å)\t(km s−1)\t(km s−1)\t(km s−1)\r\nBroad Emission Lines\r\nHα\t6562.8\t1024 ± 21\t3010 ± 450\t−7 ± 16\r\nHe i\t6678.2\t1041 ± 792\t3890 ± 2083\t−137 ± 151\r\nHe i\t7065.2\t473 ± 116\t1000 ± 600\t−136 ± 82\r\nO i\t8446.4\t562 ± 331\t1120 ± 590\t+39 ± 80\r\nPa10\t9014.9\t766 ± 202\t2100 ± 600\t−155 ± 39\r\nPa9\t9229.0\t766 ± 202\t2100 ± 600\t−155 ± 39\r\nPa8\t9545.6\t766 ± 202\t2100 ± 600\t−155 ± 39\r\nPaδ\t10049.4\t1672 ± 458\t3500 ± 400\t+23 ± 44\r\nHe i\t10830.3\t536 ± 45\t2760 ± 220\t+154 ± 22\r\nPaγ\t10938.1\t1035 ± 322\t2400 ± 260\t−75 ± 31\r\nO i\t11287.0\t1188 ± 1099\t4300 ± 2000\t+245 ± 214\r\nAbsorption Lines\r\nHα\t6562.8\t1000 ± 123\t⋯\t−200 ± 32\r\nHe i\t7065.2\t587 ± 1024\t⋯\t−52 ± 83\r\nHe i\t10830.3\t794 ± 21\t⋯\t+45 ± 22\r\nNote. Velocity offsets (Δv) calculated relative to [S iii] λ9071 at z = 3.50102.\r\n\r\nDownload table as: \r\nASCIITypeset image\r\n\r\n3.3.1. Hα Complex\r\nHα is modeled with independent narrow, broad, and absorption components. [O i] λ6302 and He i λ6680 are modeled with narrow and broad profiles. [N ii] lines are fixed at a 1:3 ratio and share kinematics; [S ii] lines have independent amplitudes but tied velocities and widths.\r\n\r\nWe find that broad Hα and He i λ6680 are strongly favored to have exponential wings (ΔBIC ∼ −500), yielding a FWHM (of the intrinsic Gaussian core) of ∼1000 km s−1—significantly narrower than the ∼3000 km s−1 derived from pure Gaussians. Although no distinct Hα absorption component is explicitly detected, likely due to insufficient resolution, the overall asymmetry of the line is best reproduced when a weak, blueshifted absorber is included in the fit. This may indicate subtle self-absorption or partial obscuration within the dense cocoon. We return to the implications of this profile shape later.\r\n\r\n3.3.2. He i λ7065\r\nThe He i λ7065 line shows a prominent blueshifted absorption component. We fit it with narrow, broad, and absorption profiles. The rest of the lines, including [Ar iii] λ7138, Fe ii λ7156, and the [O ii] triplet (λλ7323, 7325, 7332), are modeled as independent narrow lines.\r\n\r\nHe i λ7065 shows a strong preference for an exponential profile (ΔBIC ∼ − 16) with a FWHM = 473 ± 116 km s−1. A residual bump spanning from ∼λ7290 to λ7320 is likely a combination of multiple Fe ii, such as λ7290, λ7308, and potentially Fe iii λ7319.65 lines. Curiously, the latter line is often labeled as “hazy” in various emission-line libraries (e.g., A. Kramida et al. 2024), reflecting its undefined shape as a result of pressure broadening or scattering in very dense gas.\r\n\r\n3.3.3. O i λ8448 and Iron Lines\r\nIn this part of the spectrum the O i λ8448 is fit with narrow and broad components. All of the iron lines, including Fe ii λλ8228, 8239, 8289, 8470, 8490 as well as a potential Fe iii λ8306, are fit as narrow lines with shared kinematics. O i components are fit independently.\r\n\r\nWe find that the broad O i component is best described by a standard Gaussian profile, with a stronger statistical preference over exponential wings (ΔBIC ∼ 4). However, we caution that a trough at ∼3.77 μm, likely an artifact, may affect the reliability of the fit in this region.\r\n\r\n3.3.4. Iron Forest and Paschen Lines\r\nThis spectral region is among the most complex, due to the dense clustering of emission features. The Paschen lines Pa10–Pa8 are modeled with narrow and broad components. To reduce the number of free parameters, we tie all narrow Paschen components together kinematically, and do the same for the broad components. Fe ii λλ9075, 9125, 9134,9179, 9204, 9394 are fit with a shared centroid and width. [S iii] lines are fit independently.\r\n\r\nThe [S iii] λ9071 line is used to define the systemic redshift: z = 3.50102 ± 0.00019. This is done because forbidden lines, such as [S iii] or [O iii], have lower critical densities that are incompatible with the dense-gas envelopes giving rise to the other lines we observe. These lines may instead come from the host galaxy itself (e.g., R. Maiolino et al. 2024), and we therefore choose this line to define the overall redshift of the system and to measure all the offsets relative to it. All velocity offsets discussed in the subsequent sections are computed relative to this reference frame. The Paschen lines show strong preference for exponential wings (ΔBIC ∼ −38), with a FWHM = 766 ± 202 km s−1—narrower than Hα, but consistent within 2σ.\r\n\r\n3.3.5. Paδ\r\nThe Fe ii λ9997 and Paδ complex is modeled with an independent narrow component for Fe ii and both narrow and broad components for Paδ. There is no evidence for absorption. Exponential wings are again preferred (ΔBIC ∼ −26). The resulting FWHM of 1672 ± 458 km s−1 is notably larger than those of both higher-order Paschen lines and Hα, though still consistent with the latter within 2σ. It is also possible that the line shape is impacted by Fe ii λ9997 and the undetected (but likely present) Fe ii λλ10131, 10173 lines.\r\n\r\n3.3.6. He i λ10830 and Paγ\r\nThe final window contains a complicated blend of broad He i λ10830 and Paγ lines, with a clear blueshifted absorption in the former. We fit three components (narrow, broad, and absorption) to He iλ10830 and narrow plus broad components to Paγ, keeping everything kinematically independent. We fit narrow Fe ii lines at 10490, 10501, and 11128 Å with fixed redshift and line width. Finally, O i λ11290 is fit with independent narrow and broad components. Exponential wings are again preferred over a pure Gaussian profile.\r\n\r\n4. Data Analysis\r\n4.1. Morphology\r\nLRDs are unresolved in the rest-optical by definition, with measured sizes consistent with the PSF HWHM ( in F444W), and in some cases even smaller when dithers align favorably (e.g., I. Labbé et al. 2025). Gravitational lensing can further push constraints on their intrinsic sizes to ≲100 pc (L. J. Furtak et al. 2024).\r\n\r\nIn the rest-UV, however, a more complex picture is emerging. Several studies have now reported faint, extended, asymmetric components adjacent to the compact core (V. Kokorev et al. 2024b; I. Labbe et al. 2024; J. Matthee et al. 2024; P. Rinaldi et al. 2025a, 2025b), often suppressed by surface-brightness dimming. As shown in Figure 1, GLIMPSE-17775 likewise consists of two components out to F200W (rest ∼ 4000 Å), coincident with the Balmer break. However, we note that the break itself is much weaker than found in objects with very similar spectra (e.g., B. Wang et al. 2024; see Figure 3). At longer wavelengths, a point-source (PS) morphology dominates, consistent with a black-hole-dominated core. To quantify this transition, we model the NIRCam imaging using PYSERSIC (I. Pasha & T. B. Miller2023) with a minimal configuration: a fixed-center PS plus a freely offset Sérsic profile. Normalizations, n, and reff are all allowed to vary, and uncertainties are drawn from the Markov Chain Monte Carlo posteriors (e.g., V. Kokorev et al. 2024a).\r\n\r\nZoom InZoom OutReset image size\r\nFigure 3. The diversity of Balmer breaks in LRDs. The black points show the HST and JWST GLIMPSE photometry of GLIMPSE-17775. The blue line shows best-fit EAZY SED fit to the photometry only, fixing the redshift to the zspec. The maroon line show the combined and photometry-corrected G395M spectrum. While the red color in F200W–F277W is partially influenced by a bright Hα line, the Balmer break between F150W and F200W is still prominent. We further show spectra of various other LRDs (I. Labbe et al. 2024; B. Wang et al. 2024; A. de Graaff et al. 2025b; R. P. Naidu et al. 2025; A. J. Taylor et al. 2025), all shifted to z = 3.501 and normalized at 5100 Å. Finally, we show HST (blue) and JWST (orange) filter transmission curves below.\r\n\r\nDownload figure:\r\n\r\nStandard imageHigh-resolution image\r\nOur fits show that the host galaxy dominates up to λrest ∼ 4000 Å, where the host and nucleus contribute roughly equally, beyond which the PS prevails to λrest ∼ 1 μm. Because the NIRCam LW detector has ≳2× poorer resolution than the SW, a clean separation of host and nucleus in the rest-optical is impractical (see, e.g., K. E. Whalen et al. 2026). Fortunately, F200W lies at the transition where both the resolution and flux ratio are favorable, so we use that band to illustrate our galaxy/LRD decomposition. We illustrate this in Figure 4, which also shows the increasing PS fraction with wavelength, while acknowledging the uncertainties at longer wavelengths.\r\n\r\nZoom InZoom OutReset image size\r\nFigure 4. Top: two-component Sérsic+point-source (PS) fit to the F200W morphology of GLIMPSE-17775. Panels show, from left to right, the data, best-fit model, model with the extended component removed, and residuals. Bottom: fractional PS contribution vs. rest-frame wavelength. Shaded regions mark SW (blue) and LW (red) detectors, where the lower resolution of LW filters hinders reliable two-component decomposition.\r\n\r\nDownload figure:\r\n\r\nStandard imageHigh-resolution image\r\nAfter applying the lensing correction, we find that the extended component dominating the UV light has a radius of reff ∼ 1000 pc, whereas the actual compact LRD, dominant in the rest-optical, is fully consistent with the PSF and reff < 300 pc.\r\n\r\n4.2. Dust Attenuation\r\nThe ratio between observed emission-line fluxes is commonly used to estimate dust extinction. For LRDs, this has typically been achieved through the Balmer decrement, provided that multiple Balmer lines are available. In our case, only Hα is detected. While the Paschen series, of which five lines are observed, could, in principle, be used to estimate extinction, the likely presence of stratified dense gas in LRDs (A. de Graaff et al. 2025b; R. P. Naidu et al. 2025) implies that the intrinsic line ratios may deviate significantly from standard Case B recombination expectations (S.-J. Chang et al. 2026). Further, at the wavelengths of the Paschen series, the attenuation curves are practically flat (e.g., D. Calzetti et al. 2000). Small offsets of the Case B ratios would have a significant effect on the derived dust attenuation, but in return require extreme precision on measured line fluxes to be meaningful. Our uncertainties on, e.g., Paγ/Paδ are small, roughly 10%–15%, yet this still leads to an impractically high uncertainty on AV. To circumvent this limitation, we instead employ the ratio between the permitted O i λ8448 and O i λ11290 lines.\r\n\r\nThese transitions share a common energy level, and under the assumption of Bowen (Lyβ) fluorescence, all transitions through the λ11290 transition also cascade through the λ8448. This makes their intrinsic intensity set solely by the ratio of the inverse of their wavelengths.\r\n\r\nTo ensure we are comparing the same physical gas component, we isolate the narrow emission peaks in both transitions, which show consistent widths of FWHM ∼ 250 km s−1. This similarity supports the use of their flux ratio as a dust probe. We adopt the Small Magellanic Cloud (SMC) attenuation curve (K. D. Gordon et al. 2003), widely used for high-redshift galaxies and reddened AGN (P. F. Hopkins et al. 2004; P. L. Capak et al. 2015; N. A. Reddy et al. 2015, 2018; V. Kokorev et al. 2023; A. J. Taylor et al. 2025). Assuming an intrinsic ratio of (8448/11290)int = 1.336 (D. E. Osterbrock1989), we infer AV = 0.1 ± 0.3 mag, consistent with negligible extinction.\r\n\r\nWe caution, however, that this ratio probes only the narrow-line-emitting gas, which could originate either in the host galaxy or within a narrow-line region associated with the AGN. If the latter is the case, then the red optical continuum slope (βopt ∼ 0.35) would suggest that the observed SED is intrinsically red rather than reddened by dust. If instead the narrow lines arise predominantly in the host galaxy, this constraint does not directly inform the origin of the continuum emission. Similar Case B–consistent narrow-line ratios have been reported in other LRDs (e.g., M. Brooks et al. 2025; G. P. Nikopoulos et al. 2025), where the broad lines were found to show significant departures from Case B.\r\n\r\nAlthough the wavelength coverage of the red grating does not allow a Balmer decrement test for the broad-line emission (only Hα is detected), we can perform a consistency check using the brightest broad Paschen lines (Paγ, Paδ, and Pa8). Adopting intrinsic Case B ratios from P. J. Storey & D. G. Hummer (1995; Paγ/Paδ ≃ 1.5 and Paδ/Pa8 ≃ 1.8), and comparing these to our measured values of Paγ/Paδ = 1.77 ± 0.15 and Paδ/Pa8 = 1.94 ± 0.20, we find the broad Paschen lines to be consistent with Case B within ≃2σ, particularly when systematic uncertainties from blending and profile decomposition are taken into account. If Case B is applicable in the dense environments surrounding the central AGN, this would be consistent with a low-dust or dust-free origin for the broad-line-emitting gas.\r\n\r\n5. Line Properties\r\nOur fitting procedure yields over 40 emission and absorption features, most of which are detected at a high (S/N> 3) significance. With all the pieces in place, we now comment on the line profiles, kinematics, and the specific line species that we identify.\r\n\r\n5.1. Exponential Wings\r\nAs already noted throughout Section 4, and further highlighted in Figure 2, all permitted lines in the spectrum, with the exception of O iλ8448, which is likely impacted by data-quality issues, are better fit when the broad component is convolved with an exponential profile. The statistical preference for this model (as measured by ΔBIC) is especially strong for our brightest line, Hα. To further demonstrate this, and to compare this fit with a more standard, Gaussian-only approach, we show both models in Figure 5. When the broad line is fit using only a Gaussian profile, large portions of the line are underfit at a ≳3σ significance level, whereas a model that includes exponential wings shows a much smoother, albeit not perfect, residual plot.\r\n\r\nZoom InZoom OutReset image size\r\nFigure 5. Exponential wings are required. Comparison of a Gaussian×exponential model (red) and a single Gaussian profile (blue) for Hα. Uncertainties are shown as vertical lines in each spectral bin, although they are too small to be visible. The exponential model provides a far superior fit, with smoother residuals and a strongly preferred ΔBIC, highlighting the necessity of exponential wings to capture the broad-line shape.\r\n\r\nDownload figure:\r\n\r\nStandard imageHigh-resolution image\r\nThis strong preference for exponential wings is consistent with expectations from electron scattering in dense, ionized gas. Unlike Gaussian profiles, which arise from Doppler broadening due to thermal and bulk motions around the supermassive black hole, exponential profiles arise in environments dominated by electron scattering (e.g., S.-J. Chang et al. 2026; V. Rusakov et al. 2026). The absence of strong broadening in the forbidden lines (e.g., [S ii], [S iii], and [N ii]) already suggests that the densities where these electron-scattered profiles originate must already exceed multiple times the critical densities of these transitions (ne > 106). Combined with the fact that these broad profiles are non-Gaussian in shape, both the likely volume and column densities are likely even higher, at ne = 108 cm−3 and Ne ∼ 1024 cm−2, respectively, as suggested by both K. Inayoshi & R. Maiolino (2025) and V. Rusakov et al. (2026).\r\n\r\nRecent work (e.g., M. Brazzini et al. 2025) argues that, in classical broad-line region (BLR) environments, an electron-scattering origin for broad wings requires similar intrinsic and scattering widths across recombination lines. We therefore examine these criteria for the hydrogen transitions and find that, within the uncertainties of our fits, both the intrinsic and exponential widths are broadly comparable among the recombination lines. However, unlike classical BLRs, LRDs are expected to be strongly stratified, with different recombination transitions forming at different depths and probing different effective electron columns (e.g., A. de Graaff et al. 2025d; A. Sneppen et al. 2026). In such a structure, strict equality of widths is not expected even if a common scattering kernel shapes the wings. The modest variations observed here are therefore consistent with electron scattering in a dense, stratified cocoon.\r\n\r\nIt is important to note that such detailed profile decomposition is only possible due to the exceptionally high S/N per pixel achieved in the line wings of our NIRSpec G395M spectrum. As emphasized in V. Rusakov et al. (2026), these features would be impossible to distinguish with shallower data or lower-resolution modes such as NIRSpec/PRISM, or even G395M exposures lacking comparable depth.\r\n\r\n5.2. Line Profiles\r\nFurther, in Figure 6, we compare the best-fit models for all broad lines. As noted previously, with the exception of O i λ8448, every broad line is better described by exponential wings, resulting in very similar overall line shapes. The main differences arise in their widths.\r\n\r\nZoom InZoom OutReset image size\r\nFigure 6. Best-fit profiles of all broad lines, oversampled and shifted to a common center. The top panel shows hydrogen recombination (Hα, black, and Paschen series), the middle panel shows O i, and the bottom panel shows He i. Shaded regions indicate 1σ uncertainties for the least-constrained lines (Paδ, O i λ11290, and He i λ6680); uncertainties for the remaining lines are omitted for clarity. We note that hydrogen and O i lines show largely similar widths, consistent with their coupling through charge exchange. By contrast, He i lines are systematically narrower, likely reflecting their distinct metastable triplet physics and formation in a less dense outer region.\r\n\r\nDownload figure:\r\n\r\nStandard imageHigh-resolution image\r\nDespite some fits having sizable uncertainties, a trend emerges across line species. Hydrogen recombination lines (with the exception of Paδ) and O i transitions consistently show comparable intrinsic FWHM values of ∼800 km s−1. This agreement is not coincidental. Neutral oxygen and ionized hydrogen have nearly identical ionization potentials, enabling rapid charge-exchange coupling between O+ + H0⇌ O0 + H+ (D. E. Osterbrock & G. J. Ferland 2006). This continual electron exchange tightly locks the spatial distribution, ionization state, and kinematics of neutral oxygen to ionized hydrogen (and vice versa), so their broad-line profiles are naturally expected to track one another. The observed similarity therefore provides an important consistency check, reinforcing that the O i emission originates in the same dense, ionized gas as the hydrogen recombination lines. In contrast, the Fe ii lines exhibit significantly narrower widths, matching the narrow cores of the permitted transitions rather than their exponential wings. This implies that the Fe ii emission arises in a cooler, less turbulent zone exterior to the scattering-dominated region, but still closely coupled to the AGN continuum source.\r\n\r\nBy contrast, He i emission is systematically narrower. He i lines such as λ7065 and λ10830 do not couple to hydrogen via charge exchange, and their lower metastable level (23S) has distinct population physics, being fed by both collisional and recombination pathways. Further, one has to take into account the radiative-transfer effects, which make it possible to radiatively excite metastable ground-state electrons. As a result, He i emission may arise from a somewhat different spatial or kinematic region than H and O. We return to this point in more detail below.\r\n\r\nTaken together, the similar FWHM of hydrogen and oxygen broad-line profiles, combined with the near-universal exponential wings seen across all permitted transitions, strongly suggests that the line shapes are set by a common, line-independent scattering kernel rather than by transition-specific processes. Electron (Thomson) scattering in a dense, ionized cocoon provides a natural explanation: It produces exponential wings of nearly identical form across species, with widths set primarily by the electron temperature and column density (typically ∼1024 cm−2), and leaves only secondary variations from species-specific excitation or optical-depth effects (e.g., S.-J. Chang et al. 2026; V. Rusakov et al. 2026). In this framework, the narrower He i lines reflect stratification within the cocoon, where He i emission arises from an outer region that has a lower density, temperature, or column density, while the bulk hydrogen and oxygen emission share a common kinematic imprint within an inner, denser region.\r\n\r\n5.3. Line Kinematics\r\nBefore we proceed to discussing the individual features in more detail, we would like to comment on the systematic velocity offsets between various line species in the spectrum of GLIMPSE-17775. As mentioned previously, we choose the redshift of the narrow forbidden [S iii] λ9701 as the systemic reference, due to it being relatively bright and isolated. We place all velocity offsets in context by plotting all values from Tables 4 and 5 in Figure 7.\r\n\r\nZoom InZoom OutReset image size\r\nFigure 7. Velocity offsets (relative to [S iii]λ9071) and FWHM for all detected lines. Narrow permitted lines are shown as maroon circles (open for forbidden), broad lines as blue, absorption as gold, and Fe ii lines as green diamonds. The shaded band marks the velocity uncertainty set by the median spectral resolution. Narrow lines align closely with the systemic redshift, while absorption features show moderate blueshifts of ∼150 km s−1.\r\n\r\nDownload figure:\r\n\r\nStandard imageHigh-resolution image\r\nWhile every fit formally yields a centroid, the significance of any offset is constrained by the spectral resolution and S/N of the data. To gauge which velocity shifts are meaningful, we adopt a conservative uncertainty of ΔV ∼ med(R)/5, with R = λ/Δλ. This corresponds to ∼60 km s−1, below which offsets are unlikely to be statistically significant.\r\n\r\nQualitatively, we do not find systematic shifts of either permitted or forbidden narrow lines relative to the systemic redshift. Iron lines also appear consistent with the systemic velocity. In contrast, the permitted broad lines, together with their associated absorption components, show a consistent blueshift of order ∼100 km s−1.\r\n\r\nSuch blueshifts are commonly interpreted as signatures of outflowing gas in the BLR, where scattering and absorption occur preferentially along outflowing sight lines. In the context of GLIMPSE-17775, this modest but systematic offset strengthens the case for a stratified cocoon, while the narrow lines trace gas in the outer regions at systemic velocity, the BLR and absorbing layers appear to be participating in bulk outflows. Confirming the detailed velocity structure, however, will require higher-resolution follow-up with the NIRSpec H-gratings (e.g., A. Saldana-Lopez et al. 2025; A. Torralba et al. 2026).\r\n\r\n5.4. Hydrogen Absorption Lines\r\nAlthough no strong hydrogen absorption lines are explicitly detected, the Hα profile (Figure 2) shows a noticeable asymmetry, with suppressed flux on the blue side of the line. This feature is best modeled by a blueshifted (∼−200 km s−1) absorption component, as already noted in Section 4. Similar nonresonant absorption signatures (e.g., Balmer lines) are now routinely observed in LRDs across a wide range of redshifts (e.g., J. E. Greene et al. 2024; V. Kokorev et al. 2024b; I. Labbe et al. 2024; X. Lin et al. 2024; A. J. Taylor et al. 2025). The presence of such absorption implies high gas densities of order n ∼ 109 cm−3 (P. B. Hall 2007; K. Inayoshi & R. Maiolino 2025). Interestingly, only atoms in the n = 2 state appear significantly populated, as we detect no evidence for Paschen absorption in any of the five lines present in our spectrum. This is not an instrumental effect of the M-grating, as we clearly detect an absorption feature in He i λ10830 but not in the immediately adjacent Paγ. This indicates that the n = 3 state is comparatively underpopulated.\r\n\r\nAnother key manifestation of the same physical mechanism is the Balmer break, corresponding to the n = ∞ → n = 2 transition limit. A prominent break is common in many LRD spectra (D. J. Setton et al. 2025), though not ubiquitous (e.g., V. Kokorev et al. 2023; R. Tripodi et al. 2025). While our spectral coverage does not extend to the Balmer limit itself, we observe a discontinuity of ∼1 mag between the F200W and F150W filters. Due to the F200W coverage of the SED, this flux jump cannot be attributed to line boosting from Hβ and the [O iii] doublet. Adopting the break parameterization of R. P. Naidu et al. (2025), we use our best-fit SED and measure fν,4050Å/fν,3670Å = 2.02 ± 0.10. Although weaker than the extreme values (∼4–7) reported for LRDz9 (A. J. Taylor et al. 2025), MoM BH*-1 (R. P. Naidu et al. 2025), or “the Cliff” (A. de Graaff et al. 2025b), this value lies close to the maximum achievable by evolved stellar populations (I. Labbe et al. 2024; B. Wang et al. 2024). However, this measurement is based on the total (PS+host) photometry. Given that the UV continuum is spatially resolved, as we have shown in Section 4.1, host-galaxy contamination may dilute the intrinsic break strength of the central component. While uncertainties on the PS/host decomposition increase significantly toward the rest-optical, we find that using the PS-only photometry produces a noticeably sharper break, increasing the inferred strength by ∼30%–50% to fν,4050Å/fν,3670Å ≈ 2.6–3.0. Although this does not allow us to robustly conclude whether the intrinsic PS break reaches the most extreme BH*-type objects (A. de Graaff et al. 2025b; R. P. Naidu et al. 2025; A. J. Taylor et al. 2025), it suggests that the Balmer discontinuity becomes stronger once the host contribution is removed, consistent with recent findings that host light can suppress the apparent break amplitude (e.g., A. de Graaff et al. 2025d; W. Q. Sun et al. 2026).\r\n\r\nTaken together, the presence of asymmetry in the Hα profile, likely caused by blueshifted Balmer absorption, and a Balmer break adds to the evidence, complementing the exponential line wings, that the emission in GLIMPSE-17775 arises from a dense, ionized cocoon of gas. The lack of a detectable Paschen break is consistent with this picture, as high densities and optical depths result in Thomson scattering while also naturally washing out higher-order continuum edges (e.g., B. Wang et al. 2025). Assuming LTE, an extremely low ratio n3/n2 ≲ 0.01 corresponds to an electron temperature of Te ∼ 5000 K or below, consistent with the warm, partially ionized gas expected in dense LRD cocoons.\r\n\r\nWe also observe moderately prominent and extremely prominent blueshifted absorption, respectively, in He i λ7065 and He i λ10830. The mechanism for this is similar, but not identical to, the hydrogen lines. We also note the prominent blueshifted absorption seen in both He i λ7065 and He i λ10830. However, the physical mechanism driving these helium features differs fundamentally from that of the hydrogen lines; we return to this in the following section.\r\n\r\n5.5. Helium Lines\r\nBoth He i λ7065 and He i λ10830 show blueshifted (∼70−80 km s−1 from the narrow-line center) absorption components with widths of ∼600−700 km s−1. Unlike the Balmer series, helium transitions are resonantly scattered, so the arguments regarding n = 2 state abundances do not apply. Before addressing the absorption itself, it is useful to consider what the observed line strengths already tell us.\r\n\r\nIn the spectrum of GLIMPSE-17775, we detect three He i lines: λ6680, λ7065, and λ10830. These originate from different physical mechanisms. The λ6680 singlet line is produced via recombination or radiative pumping, and is only weakly dependent on density. By contrast, λ7065 and λ10830 belong to the triplet system (along with λ3889, not covered by G395M), where the lower level is populated due to its very long lifetime. Electrons in this “ground state” can be collisionally or radiatively excited into higher energies, and therefore the triplet-line strengths depend strongly on density and, to a lesser extent, temperature. As emphasized by D. A. Berg et al. (2026), He i λ10830 is the most sensitive density diagnostic among these transitions, followed by λ7065. The fact that both are much stronger than λ6680 indicates that the region where they form is very dense. The prominence of λ10830 in particular already points to a high-density environment with a temperature T ≳ 104 K. Further, the broad λ6680 line has a noticeably larger FWHM than the triplet lines but is consistent with hydrogen recombination lines, which again makes sense since both originate from the same mechanism.\r\n\r\nWhat about absorption? Its presence further reinforces this picture. The lower level (23S) of the triplet system is a metastable, long-lived state that effectively acts as a ground state in dense or partially ionized gas. As a result, photons from the 23P → 23S transition can be resonantly absorbed and reemitted many times, analogous to Lyα or Mg ii. This mechanism naturally produces strong absorption features when the He i column density is high. The fact that He i λ10830 not only dominates the helium spectrum in emission but also shows the deepest absorption in the entire spectrum provides compelling evidence for a dense, ionized cocoon of gas enshrouding GLIMPSE-17775.\r\n\r\n5.6. Oxygen Lines\r\nAbove, we noted that O i λ8446 and λ11290 share very similar profiles with the hydrogen recombination lines. This is naturally expected because neutral oxygen is tightly coupled to hydrogen via charge exchange, which rapidly equilibrates the O/H ionization states in dense gas. When charge exchange is fast (high nH), the O i/O ii ratio tracks the H i/H ii ratio, so the O i-emitting gas shares the same kinematics as the hydrogen recombination region (B. T. Draine 2011). The observed agreement in FWHM between H and O i lines is therefore an important consistency check that both species originate in the same dense, partially ionized phase.\r\n\r\nA second, independent clue of high gas density and radiation field intensity comes from the excitation mechanism. The O iλ8446–λ11287 pair is the classic signature of Lyβ (Bowen) fluorescence: Lyβ pumps O i from the ground state and the ensuing cascade preferentially populates the levels that emit at 1.129 μm, which then cascade down through the 8446 Å line. In this channel, the line emissivity scales with both the neutral oxygen (or equivalently neutral hydrogen, via charge exchange) column and the local Lyβ radiation field. Therefore, producing strong O i fluorescence requires both a very bright Lyβ source and a dense neutral (or partially ionized) cocoon.\r\n\r\nFurther, we do not detect (5σ upper limit <12/[10−20 erg s−1 cm−2]) any of the other permitted O iλ7774, λ7254, and λ7790 lines, and the [O i] λ6302/O i λ8446 ratio is weak. If collisional excitation or pure recombination dominated, these lines would be comparatively strong; their absence strongly favors Bowen fluorescence as the primary driver of the observed O i emission.\r\n\r\nFinally, the velocity structure adds a natural stratification: hydrogen recombination and O i (fluorescent, charge-exchange coupled) share similar widths and profiles, while He i lines are systematically narrower. Since He i triplet transitions emerge from a metastable 23S level (with distinct, density-sensitive population pathways and resonant transfer), they likely trace a kinematically distinct layer within the same cocoon.\r\n\r\n5.7. Lyα Fluorescence in Iron Lines\r\nPermitted iron emission, primarily Fe ii and Fe iii (e.g., I. Labbe et al. 2024; R. Tripodi et al. 2025; A. Torralba et al. 2026), but in some cases extending to highly ionized species such as Fe vii (E. Lambrides et al. 2025; M. Tang et al. 2025) and Fe x (L. J. Furtak et al. 2024), has become a recurring feature in LRD spectra. In GLIMPSE-17775, the spectrum is exceptionally rich in NIR iron lines; we identify 16 Fe ii and one Fe iii transition. Understanding the origin of this emission is key to interpreting the dense-gas environment in LRDs.\r\n\r\nThe physics of Fe ii emission has long been a challenge for BLR photoionization models (M. Joly 1993). Thick, high-column-density (∼1025 cm−2) gas at the edges of the accretion disk has been invoked as a potential source (M. Joly 1987; S. Collin-Souffrin et al. 1988), where the scattering and absorption of the hard X-ray photons ionize the gas. Similarly, this would also enhance the Balmer and Paschen line luminosities. Further, extensive theoretical work has shown that Lyα fluorescence is fundamental in reproducing the observed Fe ii strengths (T. A. A. Sigut & A. K. Pradhan 1998, 2003). Lyα pumping not only boosts the UV and optical Fe ii emission, but also predicts strong lines in the NIR.\r\n\r\nThis expectation aligns closely with our observations. In Figure 8, we compare our measured Fe ii flux ratios (normalized to Fe ii λ9075) against the Lyα-pumped model predictions of T. A. A. Sigut & A. K. Pradhan (2003). With the exception of Fe ii λ9179, affected by blending with Fe ii λ9204 and Pa9, we find remarkably good agreement across the suite of detected features. In particular, the dense forest of Fe ii transitions spanning λλ9000–9200 (center-right panel in Figure 2) is reproduced almost exactly by the theoretical spectrum (see Figure 11 in T. A. A. Sigut & A. K. Pradhan 2003). We overlay the T. A. A. Sigut & A. K. Pradhan (2003) model directly on our continuum-subtracted fit in Figure 8, demonstrating that the observed Fe ii emission is fully consistent with fluorescence in dense gas near the BLR. The implication is that the majority of the Fe ii emission in GLIMPSE-17775 arises through Lyα pumping, directly tracing an extremely dense medium, ionized by an extremely luminous source, likely an accreting black hole. Given that the Fe ii lines are somewhat narrower than other permitted features, it is likely that the emitting region is located farther from the BLR—something that has already been shown in a classic example of a narrow Fe ii emitter, I Zw 1 (R. J. Rudy et al. 2000; A. O. M. Marinello et al. 2016).\r\n\r\nZoom InZoom OutReset image size\r\nFigure 8. Lyα-pumped iron emission in GLIMPSE-17775. Left: observed Fe ii flux ratios (black points), normalized to Fe iiλ9075, compared with predictions from Lyα fluorescence models of T. A. A. Sigut & A. K. Pradhan (2003, blue). The close correspondence across ∼14 lines indicates a common excitation mechanism driven by Lyα pumping in dense, partially shielded gas. Right: zoom in on the λλ9000–9400 complex, showing the remarkable agreement between the modeled continuum-subtracted Fe ii spectrum (black) and the T. A. A. Sigut & A. K. Pradhan (2003) model (blue). We show air wavelengths of each Fe ii line directly from T. A. A. Sigut & A. K. Pradhan (2003), including the blended features. Together, these comparisons support an origin in the dense inner regions of the cocoon surrounding the accreting black hole.\r\n\r\nDownload figure:\r\n\r\nStandard imageHigh-resolution image\r\nTogether with the Balmer absorption, helium triplet features, and Bowen fluorescence in O i, the iron forest adds another piece of evidence that points to a dense cocoon enshrouding the black hole.\r\n\r\n5.8. Source Properties\r\nBased on the previous discussion, we now present the likely physical properties of the black hole and its host. The coexistence of broad permitted and narrow forbidden lines indicates, as in most LRDs (R. E. Hviding et al. 2025), that the broad components originate in an AGN BLR. Following J. E. Greene & L. C. Ho (2005), we derive MBH from the luminosity and width of the broad Hα line, assuming the exponential-wing profile demonstrated in Figures 2 and 5. With a FWHMHα = 1024 ± 21 km s−1, negligible dust, and μ = 2.04, we obtain , where the dominant uncertainty arises from the J. E. Greene & L. C. Ho (2005) calibration. A purely Gaussian fit, though statistically disfavored, would yield a FWHM 3 times larger and a black hole mass nearly a dex higher. Throughout this work, we adopt the MBH from the exponential model.\r\n\r\nFurther, by assuming that the bolometric luminosity (Lbol) scales as Lbol = 130 × LHα (G. T. Richards et al. 2006), we find Lbol = (1.06 ± 0.14) × 1045 erg s–1. Using our MBH derived by assuming exponential wings, we find that this object is accreting at a super-Eddington rate, Lbol/Ledd = 1.86 ± 0.25. This is higher than the vast majority of LRDs at all redshifts (e.g., V. Kokorev et al. 2023; L. J. Furtak et al. 2024; I. Juodžbalis et al. 2024; R. Maiolino et al. 2024; H. B. Akins et al. 2025b; D. D. Kocevski et al. 2025; A. J. Taylor et al. 2025), found to accrete at sub-Eddington rates. However, recent works examining LRDs with extreme Balmer breaks derive accretion rates that exceed the Eddington limit (E. Lambrides et al. 2024; A. de Graaff et al. 2025b; R. P. Naidu et al. 2025).\r\n\r\nA recent work examining multiwavelength LRD data suggests that the bolometric luminosity emerges predominantly from the rest-frame optical, with X-ray and radio contributions being largely subdominant (J. E. Greene et al. 2026). Given the suggested dominance of optical light in LRDs, the much lower bolometric corrections (×7–10 lower) would imply lower black hole masses and total bolometric luminosities (e.g., those derived from Hα) than standard AGN prescriptions (e.g., J. E. Greene & L. C. Ho 2005) might suggest. This adjustment would lower both the inferred black hole masses and bolometric luminosities. Because these two quantities scale together, the implied super-Eddington nature of GLIMPSE-17775 would remain unchanged, although the black hole mass could decrease to ∼105.5–105.8M⊙. This interpretation is consistent with dense-gas (BH*) models, which generically predict Eddington or super-Eddington accretion in heavily obscured environments (e.g., D. Kido et al. 2025; H. Liu et al. 2025; A. Sneppen et al. 2026). A more detailed reassessment of bolometric corrections for LRDs is clearly warranted, but such an analysis lies beyond the scope of this work. For consistency with previous studies, we adopt standard AGN bolometric corrections throughout, with all derived parameters listed in Table 1.\r\n\r\nFinally, we estimate an upper limit on the stellar mass in GLIMPSE-17775. Previous studies have modeled LRDs using joint galaxy+AGN SED decomposition (e.g., V. Kokorev et al. 2023; L. J. Furtak et al. 2024), and more recently, within the BH* framework, have assumed that most of the rest-UV flux arises from the host galaxy (R. P. Naidu et al. 2025; A. J. Taylor et al. 2025). Our spatial decomposition (Figure 4) supports this assumption: The extended component contributes >80% of the rest-UV light, implying that the bulk of the stellar mass resides in this resolved structure. Given this, we adopt a simple empirical approach using the MUV–M* relation (e.g., D. P. Stark et al. 2009; I. Labbé et al. 2013) and obtain a conservative upper limit on the stellar mass of M* ≲ 107.5M⊙. This in turn gives us a black hole-to-host mass ratio of ≲0.14, which is significantly elevated from local expectations (J. E. Greene & L. C. Ho 2005), but is not as extreme as some other LRDs reported in the literature (V. Kokorev et al. 2023; L. J. Furtak et al. 2024; R. Maiolino et al. 2024).\r\n\r\n6. Discussion and Summary\r\n6.1. Dense and Ionized Gas Surrounding the AGN\r\nOur NIRSpec G395M observations of GLIMPSE-17775 reveal a remarkably consistent picture: Across independent tracers, the line emission requires an environment of extremely high density and partial ionization.\r\n\r\nFirst, the broad permitted lines are universally better fit by exponential wings, a hallmark of electron scattering in gas with ne ≳ 108 cm−3 and column densities approaching Ne ∼ 1024 cm−2. Such profiles are not reproduced by Doppler broadening alone and point to an ionized scattering medium enveloping the source. The fact that hydrogen and O i lines share consistent FWHM values further anchors this interpretation, as charge exchange tightly couples neutral oxygen to the ionization and kinematics of hydrogen.\r\n\r\nSecond, the detection of blueshifted Balmer absorption and a significant Balmer break both require high n = 2 populations and densities n ∼ 109 cm−3. Helium transitions provide a complementary view: The triplet lines λ7065 and λ10830 are both strongly enhanced relative to the singlet states and show deep blueshifted absorption, consistent with resonant scattering from the metastable 23S level. Their systematically narrower widths compared to hydrogen and oxygen suggest stratification, with helium arising from denser, more compact layers of the cocoon.\r\n\r\nThird, the O i λ8446–λ11290 pair confirms Lyβ fluorescence, requiring both a bright Lyβ radiation field and a dense reservoir of neutral gas. The absence of other permitted O i lines not fed by Lyβ strengthens this conclusion. Finally, the detection of 16 Fe ii lines, forming an incredibly rich iron forest in this LRD, matches predictions from Lyα fluorescence models, again demanding an intense radiation field and very high densities.\r\n\r\nBecause the BLR is unresolved in essentially all AGN, broad-line widths are traditionally interpreted as virial tracers of the black hole potential. In GLIMPSE-17775, the virial story alone is insufficient: The issue is not how broad the lines are, but how they broaden. The profiles exhibit extended, nearly linear wings in velocity space that are incompatible with a Gaussian. Instead, the lines are systematically and significantly better described by a model consisting of a narrow Gaussian core (virial motion) plus exponential wings, the hallmark of Thomson scattering in a dense ionized medium. Thus, the line shape encodes both gravitational kinematics and radiative-transfer physics in the surrounding cocoon. Our schematic (Figure 9) summarizes this revised view: In LRDs, broad-line profiles are not set by dynamics alone, but by the scattering environment through which the photons escape.\r\n\r\nZoom InZoom OutReset image size\r\nFigure 9. Physical picture of the dense cocoon around GLIMPSE-17775. The inner region (1) corresponds to the dense, highly ionized broad-line region (BLR) where electron scattering (orange lines) produces exponential wings, H and O I share coupled kinematics (via charge exchange and Bowen fluorescence), and strong Balmer absorption/break signatures arise. The outer layer (2) represents an intermediate-density ionized medium, where He I triplet lines show resonant absorption from the metastable 23S level and Fe II emission is driven by Lyα fluorescence. Together, these zones form a stratified cocoon enshrouding the accreting black hole. The bottom-right panel shows stacked line profiles of H, O i, He i, and Fe ii.\r\n\r\nDownload figure:\r\n\r\nStandard imageHigh-resolution image\r\nSuch conditions—high optical depths, large column densities, and evidence for radiation-dominated gas—are precisely those expected in super-Eddington accretion flows. In this regime, radiation pressure inflates the inner accretion structure, driving powerful winds and forming the very dense, partially ionized envelope we infer here. The low X-ray luminosities and weak radio emission commonly observed in LRDs (e.g., T. T. Ananna et al. 2024; M. Yue et al. 2024; H. B. Akins et al. 2025a; M. Kokubo & Y. Harikane 2025) are consistent with this picture: The X-rays are likely absorbed or thermalized within the optically thick cocoon, while dust cannot survive in such an intense radiation field (e.g., E. Lambrides et al. 2024; A. de Graaff et al. 2025b; K. Inayoshi & R. Maiolino 2025; R. P. Naidu et al. 2025; A. J. Taylor et al. 2025). Thus, the spectroscopic signatures observed in GLIMPSE-17775—exponential wings, absorption features, and fluorescence-driven metal lines—fit naturally into a scenario where super-Eddington accretion onto a low-mass black hole powers the luminous yet heavily reprocessed emission.\r\n\r\nTaken together, the exponential wings, Balmer and helium absorption, Bowen oxygen lines, and Lyα-pumped iron forest all converge on the same physical picture: GLIMPSE-17775 is enshrouded in a dense, partially ionized cocoon of gas.\r\n\r\n6.2. Final Remarks\r\nUsing a combination of the intrinsically deepest NIRCam photometry and NIRSpec G395M observations of the lensed AS1063 field, we present a detailed investigation of a LRD at z = 3.501. The spectrum of GLIMPSE-17775 is exceptionally rich, with more than 40 detected features, allowing us to probe the physical conditions of the gas with unprecedented detail. Multiple independent diagnostics converge on the presence of a dense, partially ionized cocoon heated by a powerful ionizing source.\r\n\r\nTypical of other LRDs, GLIMPSE-17775 is extremely compact in the rest-optical (reff < 300 pc) but exhibits more extended structure in the rest-UV (reff ∼ 1000 pc; Figure 1). It shows unmistakable AGN signatures through broad permitted lines (e.g., D. D. Kocevski et al. 2023; V. Kokorev et al. 2023; J. E. Greene et al. 2024; L. J. Furtak et al. 2024). The uniquely deep G395M spectrum further reveals clues to the physical origin of both its continuum and line-emission properties: We detect exponential broad-line wings, Balmer and helium absorption, Bowen-pumped O i, Fe ii emission produced by Lyα fluorescence, and evidence for rapid, potentially super-Eddington growth.\r\n\r\nTogether, these diagnostics provide one of the clearest cases yet for the BH* “dense cocoon” scenario (A. de Graaff et al. 2025b; K. Inayoshi & R. Maiolino 2025; R. P. Naidu et al. 2025; A. J. Taylor et al. 2025). The same ingredients we observe—exponential broad wings, Balmer-break absorption, He i absorption, and rich Fe ii and O i fluorescence—have been detected individually in several other bright LRDs with medium- and high-resolution spectroscopy (e.g., L. J. Furtak et al. 2024; I. Juodžbalis et al. 2024; I. Labbe et al. 2024; F. D’Eugenio et al. 2025; E. Lambrides et al. 2025; B. Wang et al. 2025; A. Torralba et al. 2026), suggesting that dense, optically thick gas may be a common feature of the population rather than an anomaly. What distinguishes GLIMPSE-17775 is that all signatures are captured simultaneously and at high S/N, allowing a self-consistent physical interpretation. If such cocoons are widespread, then super-Eddington accretion may be a typical pathway for black hole growth in LRDs, especially among the most luminous systems. Establishing how these signatures vary with luminosity and redshift will be essential for determining whether dense cocoons represent a dominant mode of early black hole assembly.\r\n\r\nThe convergence of five independent diagnostics—exponential scattering wings, Balmer-limit absorption, helium triplet physics, and two distinct fluorescence channels—leaves little doubt: GLIMPSE-17775 hosts a dense (n ∼ 108−9 cm−3), optically thick (Ne ∼ 1024 cm−2) cocoon of partially ionized gas surrounding a super-Eddington accreting black hole. This represents some of the most direct and comprehensive spectroscopic evidence to date for the dense cocoon scenario in LRDs.\r\n\r\nAcknowledgments\r\nThe authors would like to thank Aaron Sigut and Anil Pradhan for their help with understanding iron emission in active galactic nuclei. The authors would like to acknowledge the National Institute of Standards and Technology (NIST) database of spectral lines (A. Kramida et al. 2024), which made identification of less-known emission features possible. V.K., J.C., S.F., D.B., L.F., T.H., and J.M. acknowledge support from the University of Texas at Austin Cosmic Frontier Center. A.Z. acknowledges support by the Israel Science Foundation grant No. 864/23. This work is based on observations made with the NASA/ESA/CSA James Webb Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-03127. The JWST data presented in this article were obtained from the Mikulski Archive for Space Telescopes (MAST) at the Space Telescope Science Institute. The specific observations analyzed can be accessed via doi:10.17909/4byn-fe55 and doi:10.17909/zq0c-8t87. These observations are associated with programs GO #3293 and DDT #9223.\r\n\r\nFacilities: JWST - James Webb Space Telescope, HST - Hubble Space Telescope satellite.\r\n\r\nSoftware: EAZY (G. B. Brammer et al. 2008), grizli (G. Brammer 2023), msaexp (G. Brammer 2022), photutils (L. Bradley et al. 2020), pysersic (I. Pasha & T. B. Miller 2023), sep (K. Barbary 2016), SExtractor (E. Bertin & S. Arnouts1996).","doi":"10.3847/1538-4357/ae4ed7","file":[{"checksum":"464e60013bf14d087eb0968e9c81a269","file_name":"2026_AstrophysicalJour_Kokorev.pdf","file_size":2435643,"creator":"dernst","success":1,"file_id":"22313","relation":"main_file","date_updated":"2026-07-13T13:23:11Z","date_created":"2026-07-13T13:23:11Z","content_type":"application/pdf","access_level":"open_access"}],"oa_version":"Published Version","publication_status":"published","volume":1004,"article_number":"153","DOAJ_listed":"1","type":"journal_article","fulldoi":"https://doi.org/10.3847/1538-4357/ae4ed7","dataavailabilitystatement":"The specific observations analyzed can be accessed via doi:10.17909/4byn-fe55 and doi:10.17909/zq0c-8t87. These observations are associated with programs GO #3293 and DDT #9223.\r\n\r\nFacilities: JWST - James Webb Space Telescope, HST - Hubble Space Telescope satellite.\r\n\r\nSoftware: EAZY (G. B. Brammer et al. 2008), grizli (G. Brammer 2023), msaexp (G. Brammer 2022), photutils (L. Bradley et al. 2020), pysersic (I. Pasha & T. B. Miller 2023), sep (K. Barbary 2016), SExtractor (E. Bertin & S. Arnouts1996).","scopus_import":"1","publisher":"IOP Publishing","tmp":{"name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","image":"/images/cc_by.png","short":"CC BY (4.0)","legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode"},"author":[{"last_name":"Kokorev","first_name":"Vasily","full_name":"Kokorev, Vasily"},{"full_name":"Chisholm, John","first_name":"John","last_name":"Chisholm"},{"full_name":"Naidu, Rohan P.","last_name":"Naidu","first_name":"Rohan P."},{"last_name":"Fujimoto","first_name":"Seiji","full_name":"Fujimoto, Seiji"},{"full_name":"Atek, Hakim","last_name":"Atek","first_name":"Hakim"},{"full_name":"Brammer, Gabriel","last_name":"Brammer","first_name":"Gabriel"},{"last_name":"Finkelstein","first_name":"Steven L.","full_name":"Finkelstein, Steven L."},{"full_name":"Akins, Hollis B.","last_name":"Akins","first_name":"Hollis B."},{"full_name":"Berg, Danielle A.","last_name":"Berg","first_name":"Danielle A."},{"full_name":"Furtak, Lukas J.","first_name":"Lukas J.","last_name":"Furtak"},{"full_name":"Fei, Qinyue","last_name":"Fei","first_name":"Qinyue"},{"last_name":"Hsiao","first_name":"Tiger Yu-Yang","full_name":"Hsiao, Tiger Yu-Yang"},{"full_name":"Labbé, Ivo","first_name":"Ivo","last_name":"Labbé"},{"orcid":"0000-0003-2871-127X","full_name":"Matthee, Jorryt J","first_name":"Jorryt J","id":"7439a258-f3c0-11ec-9501-9df22fe06720","last_name":"Matthee"},{"first_name":"Julian B.","last_name":"Muñoz","full_name":"Muñoz, Julian B."},{"first_name":"Pascal A.","last_name":"Oesch","full_name":"Oesch, Pascal A."},{"first_name":"Richard","last_name":"Pan","full_name":"Pan, Richard"},{"full_name":"Rinaldi, Pierluigi","first_name":"Pierluigi","last_name":"Rinaldi"},{"last_name":"Saldana-Lopez","first_name":"Alberto","full_name":"Saldana-Lopez, Alberto"},{"full_name":"Schaerer, Daniel","last_name":"Schaerer","first_name":"Daniel"},{"full_name":"Volonteri, Marta","last_name":"Volonteri","first_name":"Marta"},{"last_name":"Zitrin","first_name":"Adi","full_name":"Zitrin, Adi"}],"oa":1,"has_accepted_license":"1","month":"06","external_id":{"arxiv":["2511.07515"]},"department":[{"_id":"JoMa"}],"year":"2026","OA_type":"gold","date_created":"2026-07-13T09:48:38Z","citation":{"ieee":"V. Kokorev <i>et al.</i>, “The Deepest GLIMPSE of a dense gas cocoon enshrouding a Little Red Dot,” <i>The Astrophysical Journal</i>, vol. 1004, no. 2. IOP Publishing, 2026.","ista":"Kokorev V, Chisholm J, Naidu RP, Fujimoto S, Atek H, Brammer G, Finkelstein SL, Akins HB, Berg DA, Furtak LJ, Fei Q, Hsiao TY-Y, Labbé I, Matthee JJ, Muñoz JB, Oesch PA, Pan R, Rinaldi P, Saldana-Lopez A, Schaerer D, Volonteri M, Zitrin A. 2026. The Deepest GLIMPSE of a dense gas cocoon enshrouding a Little Red Dot. The Astrophysical Journal. 1004(2), 153.","chicago":"Kokorev, Vasily, John Chisholm, Rohan P. Naidu, Seiji Fujimoto, Hakim Atek, Gabriel Brammer, Steven L. Finkelstein, et al. “The Deepest GLIMPSE of a Dense Gas Cocoon Enshrouding a Little Red Dot.” <i>The Astrophysical Journal</i>. IOP Publishing, 2026. <a href=\"https://doi.org/10.3847/1538-4357/ae4ed7\">https://doi.org/10.3847/1538-4357/ae4ed7</a>.","mla":"Kokorev, Vasily, et al. “The Deepest GLIMPSE of a Dense Gas Cocoon Enshrouding a Little Red Dot.” <i>The Astrophysical Journal</i>, vol. 1004, no. 2, 153, IOP Publishing, 2026, doi:<a href=\"https://doi.org/10.3847/1538-4357/ae4ed7\">10.3847/1538-4357/ae4ed7</a>.","apa":"Kokorev, V., Chisholm, J., Naidu, R. P., Fujimoto, S., Atek, H., Brammer, G., … Zitrin, A. (2026). The Deepest GLIMPSE of a dense gas cocoon enshrouding a Little Red Dot. <i>The Astrophysical Journal</i>. IOP Publishing. <a href=\"https://doi.org/10.3847/1538-4357/ae4ed7\">https://doi.org/10.3847/1538-4357/ae4ed7</a>","short":"V. Kokorev, J. Chisholm, R.P. Naidu, S. Fujimoto, H. Atek, G. Brammer, S.L. Finkelstein, H.B. Akins, D.A. Berg, L.J. Furtak, Q. Fei, T.Y.-Y. Hsiao, I. Labbé, J.J. Matthee, J.B. Muñoz, P.A. Oesch, R. Pan, P. Rinaldi, A. Saldana-Lopez, D. Schaerer, M. Volonteri, A. Zitrin, The Astrophysical Journal 1004 (2026).","ama":"Kokorev V, Chisholm J, Naidu RP, et al. The Deepest GLIMPSE of a dense gas cocoon enshrouding a Little Red Dot. <i>The Astrophysical Journal</i>. 2026;1004(2). doi:<a href=\"https://doi.org/10.3847/1538-4357/ae4ed7\">10.3847/1538-4357/ae4ed7</a>"},"status":"public","issue":"2","day":"10","_id":"22296","language":[{"iso":"eng"}],"arxiv":1,"title":"The Deepest GLIMPSE of a dense gas cocoon enshrouding a Little Red Dot","ddc":["520"],"date_updated":"2026-07-13T13:25:09Z","date_published":"2026-06-10T00:00:00Z","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","intvolume":"      1004","supplementarymaterial":"no","publication_identifier":{"eissn":["1538-4357"],"issn":["0004-637X"]},"file_date_updated":"2026-07-13T13:23:11Z","OA_place":"publisher","das_tickbox":"1"}]