[{"status":"public","citation":{"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>.","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.","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>","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>.","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).","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>","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."},"OA_type":"gold","month":"06","type":"journal_article","issue":"2","doi":"10.3847/1538-4357/ae6248","article_number":"244","intvolume":"      1003","article_processing_charge":"Yes","ddc":["520"],"title":"A GLIMPSE of intermediate mass Black Holes in the epoch of reionization: Witnessing the descendants of direct collapse?","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","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","file_date_updated":"2026-06-22T08:03:55Z","date_created":"2026-06-14T22:01:43Z","_id":"21999","publication":"The Astrophysical Journal","quality_controlled":"1","day":"01","article_type":"original","oa":1,"researchdata_availability":"yes","oa_version":"Published Version","publication_identifier":{"eissn":["1538-4357"],"issn":["0004-637X"]},"PlanS_conform":"1","scopus_import":"1","OA_place":"publisher","supplementarymaterial":"yes","author":[{"full_name":"Fei, Qinyue","last_name":"Fei","first_name":"Qinyue"},{"full_name":"Fujimoto, Seiji","last_name":"Fujimoto","first_name":"Seiji"},{"full_name":"Naidu, Rohan P.","last_name":"Naidu","first_name":"Rohan P."},{"first_name":"John","last_name":"Chisholm","full_name":"Chisholm, John"},{"last_name":"Atek","full_name":"Atek, Hakim","first_name":"Hakim"},{"first_name":"Gabriel","last_name":"Brammer","full_name":"Brammer, Gabriel"},{"full_name":"Asada, Yoshihisa","last_name":"Asada","first_name":"Yoshihisa"},{"first_name":"Danielle A.","last_name":"Berg","full_name":"Berg, Danielle A."},{"last_name":"Bromm","full_name":"Bromm, Volker","first_name":"Volker"},{"full_name":"Furtak, Lukas J.","last_name":"Furtak","first_name":"Lukas J."},{"last_name":"Greene","full_name":"Greene, Jenny E.","first_name":"Jenny E."},{"full_name":"Hsiao, Tiger Yu Yang","last_name":"Hsiao","first_name":"Tiger Yu Yang"},{"first_name":"Junehyoung","last_name":"Jeon","full_name":"Jeon, Junehyoung"},{"last_name":"Kokorev","full_name":"Kokorev, Vasily","first_name":"Vasily"},{"full_name":"Matthee, Jorryt J","last_name":"Matthee","orcid":"0000-0003-2871-127X","first_name":"Jorryt J","id":"7439a258-f3c0-11ec-9501-9df22fe06720"},{"last_name":"Natarajan","full_name":"Natarajan, Priyamvada","first_name":"Priyamvada"},{"first_name":"Richard","last_name":"Pan","full_name":"Pan, Richard"},{"full_name":"Richard, Johan","last_name":"Richard","first_name":"Johan"},{"full_name":"Saldana-Lopez, Alberto","last_name":"Saldana-Lopez","first_name":"Alberto"},{"full_name":"Schaerer, Daniel","last_name":"Schaerer","first_name":"Daniel"},{"first_name":"Marta","last_name":"Volonteri","full_name":"Volonteri, Marta"},{"first_name":"Adi","full_name":"Zitrin, Adi","last_name":"Zitrin"}],"DOAJ_listed":"1","publication_status":"published","year":"2026","das_tickbox":"0","volume":1003,"has_accepted_license":"1","date_updated":"2026-06-22T11:34:52Z","publisher":"IOP Publishing","file":[{"file_size":19681834,"creator":"dernst","file_id":"22112","date_updated":"2026-06-22T08:03:55Z","success":1,"content_type":"application/pdf","file_name":"2026_AstrophysicalJour_Fei.pdf","relation":"main_file","checksum":"b04247996b8dcd0eb5387581706d1106","access_level":"open_access","date_created":"2026-06-22T08:03:55Z"}],"tmp":{"legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","short":"CC BY (4.0)","image":"/images/cc_by.png"},"external_id":{"arxiv":["2509.20452"]},"department":[{"_id":"JoMa"}],"license":"https://creativecommons.org/licenses/by/4.0/","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."}],"date_published":"2026-06-01T00:00:00Z","arxiv":1,"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.","language":[{"iso":"eng"}],"fulldoi":"https://doi.org/10.3847/1538-4357/ae6248"},{"title":"An eclipsing 8.56 minutes orbital period mass-transferring binary","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","day":"01","quality_controlled":"1","article_type":"original","oa":1,"file_date_updated":"2026-05-04T06:36:00Z","date_created":"2026-04-12T22:01:47Z","_id":"21705","publication":"The Astrophysical Journal","type":"journal_article","issue":"2","citation":{"ama":"Chickles ET, Chakraborty J, Burdge KB, et al. An eclipsing 8.56 minutes orbital period mass-transferring binary. <i>The Astrophysical Journal</i>. 2026;1000(2). doi:<a href=\"https://doi.org/10.3847/1538-4357/ae4871\">10.3847/1538-4357/ae4871</a>","ista":"Chickles ET, Chakraborty J, Burdge KB, Dhillon VS, Draghis P, El-Badry K, Green MJ, Householder A, Hughes S, Layden C, Littlefair SP, Munday J, Pelisoli I, Redden MS, Tonry J, van Roestel JC, Angile FE, Brown AJ, Segura NC, Dinsmore J, Dyer M, Furesz G, Gabutti M, Garbutt J, García-Mejía J, Jarvis D, Kennedy MR, Kerry P, Mccormac J, Mo G, Osip D, Parsons S, Pike E, Piotrowski JJ, Romani RW, Sahman D, Simcoe R. 2026. An eclipsing 8.56 minutes orbital period mass-transferring binary. The Astrophysical Journal. 1000(2), 237.","short":"E.T. Chickles, J. Chakraborty, K.B. Burdge, V.S. Dhillon, P. Draghis, K. El-Badry, M.J. Green, A. Householder, S. Hughes, C. Layden, S.P. Littlefair, J. Munday, I. Pelisoli, M.S. Redden, J. Tonry, J.C. van Roestel, F.E. Angile, A.J. Brown, N.C. Segura, J. Dinsmore, M. Dyer, G. Furesz, M. Gabutti, J. Garbutt, J. García-Mejía, D. Jarvis, M.R. Kennedy, P. Kerry, J. Mccormac, G. Mo, D. Osip, S. Parsons, E. Pike, J.J. Piotrowski, R.W. Romani, D. Sahman, R. Simcoe, The Astrophysical Journal 1000 (2026).","chicago":"Chickles, Emma T., Joheen Chakraborty, Kevin B. Burdge, Vik S. Dhillon, Paul Draghis, Kareem El-Badry, Matthew J. Green, et al. “An Eclipsing 8.56 Minutes Orbital Period Mass-Transferring Binary.” <i>The Astrophysical Journal</i>. IOP Publishing, 2026. <a href=\"https://doi.org/10.3847/1538-4357/ae4871\">https://doi.org/10.3847/1538-4357/ae4871</a>.","apa":"Chickles, E. T., Chakraborty, J., Burdge, K. B., Dhillon, V. S., Draghis, P., El-Badry, K., … Simcoe, R. (2026). An eclipsing 8.56 minutes orbital period mass-transferring binary. <i>The Astrophysical Journal</i>. IOP Publishing. <a href=\"https://doi.org/10.3847/1538-4357/ae4871\">https://doi.org/10.3847/1538-4357/ae4871</a>","ieee":"E. T. Chickles <i>et al.</i>, “An eclipsing 8.56 minutes orbital period mass-transferring binary,” <i>The Astrophysical Journal</i>, vol. 1000, no. 2. IOP Publishing, 2026.","mla":"Chickles, Emma T., et al. “An Eclipsing 8.56 Minutes Orbital Period Mass-Transferring Binary.” <i>The Astrophysical Journal</i>, vol. 1000, no. 2, 237, IOP Publishing, 2026, doi:<a href=\"https://doi.org/10.3847/1538-4357/ae4871\">10.3847/1538-4357/ae4871</a>."},"status":"public","OA_type":"gold","month":"04","ddc":["520"],"article_processing_charge":"Yes","intvolume":"      1000","article_number":"237","doi":"10.3847/1538-4357/ae4871","external_id":{"arxiv":["2601.07925"]},"tmp":{"legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","short":"CC BY (4.0)","image":"/images/cc_by.png"},"file":[{"creator":"dernst","file_size":1225916,"file_name":"2026_AstrophysicalJournal_Chickles.pdf","date_created":"2026-05-04T06:36:00Z","access_level":"open_access","checksum":"c8f64a78f36224d8e0ea1f324e43e389","relation":"main_file","file_id":"21782","date_updated":"2026-05-04T06:36:00Z","success":1,"content_type":"application/pdf"}],"fulldoi":"https://doi.org/10.3847/1538-4357/ae4871","arxiv":1,"acknowledgement":"This work has made use of data from the Asteroid Terrestrial-impact Last Alert System (ATLAS) project. The Asteroid Terrestrial-impact Last Alert System (ATLAS) project is primarily funded to search for near-Earth asteroids through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogs from the survey area. This work was partially funded by Kepler/K2 grant J1944/80NSSC19K0112 and HST GO-15889 and STFC grants ST/T000198/1 and ST/S006109/1. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, the Queen’s University Belfast, the Space Telescope Science Institute, the South African Astronomical Observatory, and the Millennium Institute of Astrophysics (MAS), Chile. VSD and ULTRACAM are supported by STFC grant ST/Z000033/1. J.G.M. gratefully acknowledges support from the Heising-Simons Foundation and the Pappalardo family through the MIT Pappalardo Fellowship in Physics.","language":[{"iso":"eng"}],"date_published":"2026-04-01T00:00:00Z","department":[{"_id":"IlCa"}],"abstract":[{"lang":"eng","text":"We report the discovery of ATLAS J101342.5−451656.8 (hereafter ATLAS J1013−4516), an 8.56 minute orbital-period mass-transferring AM Canum Venaticorum (AM CVn) binary with a mean Gaia magnitude of G = 19.51, identified via periodic variability in light curves from the Asteroid Terrestrial-impact Last Alert System (ATLAS) of Gaia white dwarf candidates. Follow-up with the Large Lenslet Array Magellan Spectrograph shows a helium-dominated accretion disk, and high-speed ULTRACAM photometry reveals pronounced primary and secondary eclipses. We construct a decade-long timing baseline leveraging light curves from the ATLAS and Gaia surveys, as well as the high-speed imagers ULTRACAM on the New Energy Telescope and proto-Lightspeed on the Magellan Clay telescope. From this timing baseline, we measure an orbital period derivative of P 1.60 0.07 10 = ± × 12 s s−1. Interpreted in the context of stable mass transfer, the magnitude and sign of P indicate that the orbital evolution is governed by the interplay between gravitationalwave-driven angular-momentum losses and mass transfer, directly probing the donor’s structural response to mass loss. We constrain the accretor and donor mass based on stable mass-transfer arguments assuming angularmomentum loss dominated by gravitational-wave emission, allowing us to infer the characteristic gravitational\r\nwave strain of the binary for future space-based GW observatories such as the Laser Interferometer Space Antenna (LISA). We predict a characteristic strain corresponding to a 4 yr LISA signal-to-noise ratio ≳10, establishing ATLAS J1013−4516 as a strong prospective LISA source that will probe long-term orbital evolution in the mass-transferring regime."}],"publication_identifier":{"issn":["0004-637X"],"eissn":["1538-4357"]},"oa_version":"Published Version","has_accepted_license":"1","date_updated":"2026-05-04T06:37:12Z","publisher":"IOP Publishing","year":"2026","volume":1000,"DOAJ_listed":"1","publication_status":"published","scopus_import":"1","OA_place":"publisher","author":[{"last_name":"Chickles","full_name":"Chickles, Emma T.","first_name":"Emma T."},{"first_name":"Joheen","full_name":"Chakraborty, Joheen","last_name":"Chakraborty"},{"full_name":"Burdge, Kevin B.","last_name":"Burdge","first_name":"Kevin B."},{"full_name":"Dhillon, Vik S.","last_name":"Dhillon","first_name":"Vik S."},{"last_name":"Draghis","full_name":"Draghis, Paul","first_name":"Paul"},{"full_name":"El-Badry, Kareem","last_name":"El-Badry","first_name":"Kareem"},{"first_name":"Matthew J.","last_name":"Green","full_name":"Green, Matthew J."},{"first_name":"Aaron","full_name":"Householder, Aaron","last_name":"Householder"},{"first_name":"Sarah","last_name":"Hughes","full_name":"Hughes, Sarah"},{"first_name":"Christopher","last_name":"Layden","full_name":"Layden, Christopher"},{"first_name":"Stuart P.","full_name":"Littlefair, Stuart P.","last_name":"Littlefair"},{"full_name":"Munday, James","last_name":"Munday","first_name":"James"},{"full_name":"Pelisoli, Ingrid","last_name":"Pelisoli","first_name":"Ingrid"},{"first_name":"Maya S.","full_name":"Redden, Maya S.","last_name":"Redden"},{"last_name":"Tonry","full_name":"Tonry, John","first_name":"John"},{"id":"4d122fc8-6083-11f0-87a5-97d68b860333","first_name":"Joannes C","full_name":"van Roestel, Joannes C","last_name":"van Roestel"},{"first_name":"Francesco Elio","last_name":"Angile","full_name":"Angile, Francesco Elio"},{"first_name":"Alex J.","last_name":"Brown","full_name":"Brown, Alex J."},{"full_name":"Segura, Noel Castro","last_name":"Segura","first_name":"Noel Castro"},{"last_name":"Dinsmore","full_name":"Dinsmore, Jack","first_name":"Jack"},{"last_name":"Dyer","full_name":"Dyer, Martin","first_name":"Martin"},{"full_name":"Furesz, Gabor","last_name":"Furesz","first_name":"Gabor"},{"first_name":"Michelle","last_name":"Gabutti","full_name":"Gabutti, Michelle"},{"first_name":"James","last_name":"Garbutt","full_name":"Garbutt, James"},{"last_name":"García-Mejía","full_name":"García-Mejía, Juliana","first_name":"Juliana"},{"first_name":"Daniel","full_name":"Jarvis, Daniel","last_name":"Jarvis"},{"first_name":"Mark R.","full_name":"Kennedy, Mark R.","last_name":"Kennedy"},{"first_name":"Paul","full_name":"Kerry, Paul","last_name":"Kerry"},{"first_name":"James","full_name":"Mccormac, James","last_name":"Mccormac"},{"first_name":"Geoffrey","full_name":"Mo, Geoffrey","last_name":"Mo"},{"first_name":"Dave","full_name":"Osip, Dave","last_name":"Osip"},{"first_name":"Steven","full_name":"Parsons, Steven","last_name":"Parsons"},{"first_name":"Eleanor","full_name":"Pike, Eleanor","last_name":"Pike"},{"full_name":"Piotrowski, John J.","last_name":"Piotrowski","first_name":"John J."},{"first_name":"Roger W.","full_name":"Romani, Roger W.","last_name":"Romani"},{"full_name":"Sahman, David","last_name":"Sahman","first_name":"David"},{"full_name":"Simcoe, Rob","last_name":"Simcoe","first_name":"Rob"}]},{"intvolume":"      1000","doi":"10.3847/1538-4357/ae3b25","article_number":"111","ddc":["520"],"article_processing_charge":"Yes","OA_type":"gold","citation":{"ama":"Papovich C, Cole JW, Hu W, et al. Galaxies in the epoch of reionization are all bark and no bite-plenty of ionizing photons, low escape fractions. <i>The Astrophysical Journal</i>. 2026;1000(1). doi:<a href=\"https://doi.org/10.3847/1538-4357/ae3b25\">10.3847/1538-4357/ae3b25</a>","ista":"Papovich C, Cole JW, Hu W, Finkelstein SL, Shen L, Arrabal Haro P, Amorín RO, Backhaus BE, Bagley MB, Bhatawdekar R, Calabrò A, Carnall AC, Cleri NJ, Daddi E, Dickinson M, Grogin NA, Holwerda BW, Jaskot AE, Koekemoer AM, Llerena M, Lucas RA, Mascia S, Pacucci F, Pentericci L, Pérez-González PG, Pirzkal N, Raghunathan S, Seillé LM, Somerville RS, Yung LYA. 2026. Galaxies in the epoch of reionization are all bark and no bite-plenty of ionizing photons, low escape fractions. The Astrophysical Journal. 1000(1), 111.","chicago":"Papovich, Casey, Justin W. Cole, Weida Hu, Steven L. Finkelstein, Lu Shen, Pablo Arrabal Haro, Ricardo O. Amorín, et al. “Galaxies in the Epoch of Reionization Are All Bark and No Bite-Plenty of Ionizing Photons, Low Escape Fractions.” <i>The Astrophysical Journal</i>. IOP Publishing, 2026. <a href=\"https://doi.org/10.3847/1538-4357/ae3b25\">https://doi.org/10.3847/1538-4357/ae3b25</a>.","short":"C. Papovich, J.W. Cole, W. Hu, S.L. Finkelstein, L. Shen, P. Arrabal Haro, R.O. Amorín, B.E. Backhaus, M.B. Bagley, R. Bhatawdekar, A. Calabrò, A.C. Carnall, N.J. Cleri, E. Daddi, M. Dickinson, N.A. Grogin, B.W. Holwerda, A.E. Jaskot, A.M. Koekemoer, M. Llerena, R.A. Lucas, S. Mascia, F. Pacucci, L. Pentericci, P.G. Pérez-González, N. Pirzkal, S. Raghunathan, L.M. Seillé, R.S. Somerville, L.Y.A. Yung, The Astrophysical Journal 1000 (2026).","apa":"Papovich, C., Cole, J. W., Hu, W., Finkelstein, S. L., Shen, L., Arrabal Haro, P., … Yung, L. Y. A. (2026). Galaxies in the epoch of reionization are all bark and no bite-plenty of ionizing photons, low escape fractions. <i>The Astrophysical Journal</i>. IOP Publishing. <a href=\"https://doi.org/10.3847/1538-4357/ae3b25\">https://doi.org/10.3847/1538-4357/ae3b25</a>","ieee":"C. Papovich <i>et al.</i>, “Galaxies in the epoch of reionization are all bark and no bite-plenty of ionizing photons, low escape fractions,” <i>The Astrophysical Journal</i>, vol. 1000, no. 1. IOP Publishing, 2026.","mla":"Papovich, Casey, et al. “Galaxies in the Epoch of Reionization Are All Bark and No Bite-Plenty of Ionizing Photons, Low Escape Fractions.” <i>The Astrophysical Journal</i>, vol. 1000, no. 1, 111, IOP Publishing, 2026, doi:<a href=\"https://doi.org/10.3847/1538-4357/ae3b25\">10.3847/1538-4357/ae3b25</a>."},"month":"03","status":"public","type":"journal_article","issue":"1","file_date_updated":"2026-05-04T10:40:07Z","date_created":"2026-04-12T22:01:49Z","_id":"21710","publication":"The Astrophysical Journal","quality_controlled":"1","article_type":"original","day":"20","oa":1,"user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","title":"Galaxies in the epoch of reionization are all bark and no bite-plenty of ionizing photons, low escape fractions","publication_status":"published","scopus_import":"1","OA_place":"publisher","author":[{"first_name":"Casey","full_name":"Papovich, Casey","last_name":"Papovich"},{"first_name":"Justin W.","full_name":"Cole, Justin W.","last_name":"Cole"},{"first_name":"Weida","full_name":"Hu, Weida","last_name":"Hu"},{"first_name":"Steven L.","last_name":"Finkelstein","full_name":"Finkelstein, Steven L."},{"full_name":"Shen, Lu","last_name":"Shen","first_name":"Lu"},{"last_name":"Arrabal Haro","full_name":"Arrabal Haro, Pablo","first_name":"Pablo"},{"first_name":"Ricardo O.","last_name":"Amorín","full_name":"Amorín, Ricardo O."},{"last_name":"Backhaus","full_name":"Backhaus, Bren E.","first_name":"Bren E."},{"last_name":"Bagley","full_name":"Bagley, Micaela B.","first_name":"Micaela B."},{"last_name":"Bhatawdekar","full_name":"Bhatawdekar, Rachana","first_name":"Rachana"},{"first_name":"Antonello","last_name":"Calabrò","full_name":"Calabrò, Antonello"},{"first_name":"Adam C.","full_name":"Carnall, Adam C.","last_name":"Carnall"},{"last_name":"Cleri","full_name":"Cleri, Nikko J.","first_name":"Nikko J."},{"first_name":"Emanuele","last_name":"Daddi","full_name":"Daddi, Emanuele"},{"last_name":"Dickinson","full_name":"Dickinson, Mark","first_name":"Mark"},{"last_name":"Grogin","full_name":"Grogin, Norman A.","first_name":"Norman A."},{"full_name":"Holwerda, Benne W.","last_name":"Holwerda","first_name":"Benne W."},{"full_name":"Jaskot, Anne E.","last_name":"Jaskot","first_name":"Anne E."},{"first_name":"Anton M.","last_name":"Koekemoer","full_name":"Koekemoer, Anton M."},{"first_name":"Mario","full_name":"Llerena, Mario","last_name":"Llerena"},{"first_name":"Ray A.","last_name":"Lucas","full_name":"Lucas, Ray A."},{"last_name":"Mascia","full_name":"Mascia, Sara","id":"edaf889c-c7cd-11ef-ab1b-bb28c431bd29","first_name":"Sara"},{"first_name":"Fabio","full_name":"Pacucci, Fabio","last_name":"Pacucci"},{"last_name":"Pentericci","full_name":"Pentericci, Laura","first_name":"Laura"},{"first_name":"Pablo G.","last_name":"Pérez-González","full_name":"Pérez-González, Pablo G."},{"first_name":"Nor","last_name":"Pirzkal","full_name":"Pirzkal, Nor"},{"full_name":"Raghunathan, Srinivasan","last_name":"Raghunathan","first_name":"Srinivasan"},{"full_name":"Seillé, Lise Marie","last_name":"Seillé","first_name":"Lise Marie"},{"first_name":"Rachel S.","last_name":"Somerville","full_name":"Somerville, Rachel S."},{"full_name":"Yung, L. Y.Aaron","last_name":"Yung","first_name":"L. Y.Aaron"}],"has_accepted_license":"1","date_updated":"2026-05-04T10:44:57Z","publisher":"IOP Publishing","year":"2026","volume":1000,"oa_version":"Published Version","publication_identifier":{"eissn":["1538-4357"],"issn":["0004-637X"]},"date_published":"2026-03-20T00:00:00Z","department":[{"_id":"JoMa"}],"abstract":[{"lang":"eng","text":"Early results from JWST suggest that Epoch of Reionization (EoR) galaxies produce copious ionizing photons, which, if they escape efficiently, could cause reionization to occur too early. We study this problem using JWST imaging and prism spectroscopy for 412 galaxies at 4.5 < z < 9.0. We fit these data simultaneously with stellar population and nebular emission models that include a parameter for the fraction of ionizing photons that escape the galaxy, fesc. We find that the ionization production efficiency, ξion = Q(H0)/LUV, increases with redshift and decreasing UV luminosity, but shows significant scatter, (log ion z, MUV) 0.3 dex. The inferred escape fractions averaged over the population are low, ranging from〈fesc〉 ≃ 2.6% ± 1.4% at 6 < z < 9 to 6.5% ± 2.2% at 4.5 < z < 6, with weak or no indication of evolution with redshift. This implies that in our models most of the ionizing photons need to be absorbed to account for the nebular emission. We compute the impact of our results on reionization, including the distributions for ξion and fesc, and the evolution and uncertainty of the UV luminosity function. Considering galaxies brighter than MUV < −16 mag would produce an intergalactic medium hydrogen-ionized fraction of xe = 0.5 at 5.3 < z < 5.8, possibly too late compared to constraints from from quasistellar\r\nobject (QSO) sight lines. Including fainter galaxies, MUV < −14 mag, we obtain xe = 0.5 at 6.0 < z < 8.1, fully consistent with QSO and cosmic microwave background data. This implies that EoR galaxies produce plenty of ionizing photons, but that these do not efficiently escape. This may be a result of high gas column densities combined with burstier star formation histories, which limit the time massive stars are able to clear channels through the gas for ionizing photons to escape."}],"fulldoi":"https://doi.org/10.3847/1538-4357/ae3b25","language":[{"iso":"eng"}],"acknowledgement":"We wish to thank our colleagues in the CEERS collaboration for their hard work and valuable contributions on this project. We extend our sincerest thanks to the anonymous referee whose critical and constructive report improved the quality of this manuscript. We also thank the JADES team for providing an excellent dataset for science. We with to thank colleagues for valuable discussions, feedback, and suggestions, including John Chisholm, Kevin Huffenberger, Jessica\r\nMeh, Julian Muñoz, Irene Shivaei, Justin Spilker, Aaron Smith, and Romain Teyssier.\r\nPortions of this research were conducted with the advanced computing resources provided by Texas A&M High Performance Research Computing (HPRC, http://hprc.tamu.edu). This work benefited from support from the George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy at Texas A&M University. CP thanks Marsha and Ralph Schilling for generous support of this research. This work was partially support by the Future Investigators in NASA Earth and Space Science and Technology (FINESST) program grant No. 80NSSC23K1487. R.A. acknowledges support of grant PID2023-147386NB-I00 funded by MICIU/AEI/10.13039/501100011033 and by ERDF/EU, and the Severo Ochoa grant CEX2021-001131-S funded by MCIN/AEI/10.13039/50110001103. A.C.C. acknowledges support from a UKRI Frontier Research Guarantee Grant (PI Carnall; grant reference EP/Y037065/1) This work acknowledges support from the NASA/ESA/CSA James Webb Space Telescope through the\r\nSpace Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-03127. Support for program JWST-ERS-01345.009-A, JWST-GO-02079.013-A, JWST-GO-06368.011-A, and JWST-GO-01837.030-A, 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. This work made use of v2.2 of the Binary Population\r\nand Spectral Synthesis (BPASS) models as described in E. R. Stanway & J. J. Eldridge (2018).","arxiv":1,"file":[{"date_updated":"2026-05-04T10:40:07Z","success":1,"file_id":"21791","content_type":"application/pdf","file_name":"2026_AstrophysicalJour_Papovich.pdf","relation":"main_file","access_level":"open_access","checksum":"0031a6f197a3fa8c2845de10b6bdc696","date_created":"2026-05-04T10:40:07Z","file_size":6670398,"creator":"dernst"}],"external_id":{"arxiv":["2505.08870"]},"tmp":{"legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","short":"CC BY (4.0)","image":"/images/cc_by.png"}},{"tmp":{"legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","short":"CC BY (4.0)","image":"/images/cc_by.png"},"file":[{"file_id":"21789","success":1,"date_updated":"2026-05-04T10:24:49Z","content_type":"application/pdf","file_name":"2026_AstrophysicalJour_Lin.pdf","access_level":"open_access","date_created":"2026-05-04T10:24:49Z","checksum":"5162d1539ef7d10927ef73d8b4500017","relation":"main_file","file_size":2619679,"creator":"dernst"}],"acknowledgement":"M.C. acknowledges support by the European Union (ERC; MMMonsters, 101117624). This work was also supported in part by NASA grants 80NSSC24K0440 and 80NSSC22K0822. This research used the resources of the Center for Institutional Research Computing at Washington State University.","language":[{"iso":"eng"}],"fulldoi":"https://doi.org/10.3847/1538-4357/ae29a7","department":[{"_id":"ZoHa"}],"abstract":[{"text":"Supermassive black hole binary (SMBHB) systems are expected to form as a consequence of galaxy mergers. At subparsec separations, SMBHBs can be identified as quasars with periodic variability, with previous periodicity searches uncovering significant candidates. However, these searches focused primarily on sinusoidal signals, while theoretical models and hydrodynamical simulations predict that binaries produce more complex non-sinusoidal pulse shapes. Here we examine the efficacy of the Lomb–Scargle periodogram (LSP; one of the most popular tools for periodicity searches in unevenly sampled lightcurves) to detect periodicities with a sawtooth shape mimicking results of hydrodynamical simulations. We simulate idealized well-sampled lightcurves, lightcurves that mimic the data in the Palomar Transient Factory (PTF) analyzed in M. Charisi et al. (2016), and lightcurves that resemble our expectations for single-band data in the upcoming Legacy Survey of Space and Time (LSST) of the Rubin Observatory. We approximate quasar variability with a damped random walk (DRW) model, inject sinusoidal and sawtooth pulse shapes, and assess their statistical significance. We find that in the presence of red noise, the LSP detects a relatively low fraction of the sinusoidal signals (∼45%, ∼24%, and ∼23%, in the PTF-like, idealized, and LSST-like lightcurves, respectively). The fraction is significantly reduced for sawtooth periodicity (with only ∼9% in PTF-like and ∼1% in idealized and LSST-like lightcurves). These low recovery rates imply that previous searches have missed the large majority of binaries. They also have significant implications for the detection of SMBHBs in upcoming LSST necessitating the development of advanced tools that go beyond the simple LSP.","lang":"eng"}],"date_published":"2026-02-01T00:00:00Z","publication_identifier":{"issn":["0004-637X"],"eissn":["1538-4357"]},"oa_version":"Published Version","year":"2026","volume":997,"date_updated":"2026-05-04T10:26:59Z","has_accepted_license":"1","publisher":"IOP Publishing","OA_place":"publisher","scopus_import":"1","author":[{"first_name":"Allison","last_name":"Lin","full_name":"Lin, Allison"},{"last_name":"Charisi","full_name":"Charisi, Maria","first_name":"Maria"},{"id":"7c006e8c-cc0d-11ee-8322-cb904ef76f36","first_name":"Zoltán","orcid":"0000-0003-3633-5403","full_name":"Haiman, Zoltán","last_name":"Haiman"}],"DOAJ_listed":"1","publication_status":"published","title":"Lomb-scargle periodogram struggles with non-sinusoidal supermassive Black Hole binary signatures in quasar lightcurves","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","day":"01","quality_controlled":"1","article_type":"original","oa":1,"file_date_updated":"2026-05-04T10:24:49Z","date_created":"2026-04-12T22:01:49Z","_id":"21712","publication":"The Astrophysical Journal","type":"journal_article","issue":"2","OA_type":"gold","month":"02","status":"public","citation":{"apa":"Lin, A., Charisi, M., &#38; Haiman, Z. (2026). Lomb-scargle periodogram struggles with non-sinusoidal supermassive Black Hole binary signatures in quasar lightcurves. <i>The Astrophysical Journal</i>. IOP Publishing. <a href=\"https://doi.org/10.3847/1538-4357/ae29a7\">https://doi.org/10.3847/1538-4357/ae29a7</a>","ieee":"A. Lin, M. Charisi, and Z. Haiman, “Lomb-scargle periodogram struggles with non-sinusoidal supermassive Black Hole binary signatures in quasar lightcurves,” <i>The Astrophysical Journal</i>, vol. 997, no. 2. IOP Publishing, 2026.","mla":"Lin, Allison, et al. “Lomb-Scargle Periodogram Struggles with Non-Sinusoidal Supermassive Black Hole Binary Signatures in Quasar Lightcurves.” <i>The Astrophysical Journal</i>, vol. 997, no. 2, 316, IOP Publishing, 2026, doi:<a href=\"https://doi.org/10.3847/1538-4357/ae29a7\">10.3847/1538-4357/ae29a7</a>.","ama":"Lin A, Charisi M, Haiman Z. Lomb-scargle periodogram struggles with non-sinusoidal supermassive Black Hole binary signatures in quasar lightcurves. <i>The Astrophysical Journal</i>. 2026;997(2). doi:<a href=\"https://doi.org/10.3847/1538-4357/ae29a7\">10.3847/1538-4357/ae29a7</a>","ista":"Lin A, Charisi M, Haiman Z. 2026. Lomb-scargle periodogram struggles with non-sinusoidal supermassive Black Hole binary signatures in quasar lightcurves. The Astrophysical Journal. 997(2), 316.","short":"A. Lin, M. Charisi, Z. Haiman, The Astrophysical Journal 997 (2026).","chicago":"Lin, Allison, Maria Charisi, and Zoltán Haiman. “Lomb-Scargle Periodogram Struggles with Non-Sinusoidal Supermassive Black Hole Binary Signatures in Quasar Lightcurves.” <i>The Astrophysical Journal</i>. IOP Publishing, 2026. <a href=\"https://doi.org/10.3847/1538-4357/ae29a7\">https://doi.org/10.3847/1538-4357/ae29a7</a>."},"article_processing_charge":"Yes","ddc":["520"],"article_number":"316","intvolume":"       997","doi":"10.3847/1538-4357/ae29a7"},{"user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","title":"What you see is what you get: Empirically measured bolometric luminosities of Little Red Dots","project":[{"grant_number":"101076224","_id":"bd9b2118-d553-11ed-ba76-db24564edfea","name":"Young galaxies as tracers and agents of cosmic reionization"}],"oa":1,"quality_controlled":"1","day":"10","article_type":"original","publication":"The Astrophysical Journal","_id":"21715","date_created":"2026-04-12T22:01:50Z","file_date_updated":"2026-05-04T11:19:48Z","issue":"2","type":"journal_article","citation":{"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>","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.","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>","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>.","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)."},"status":"public","month":"01","OA_type":"gold","ddc":["520"],"article_processing_charge":"Yes","doi":"10.3847/1538-4357/ae1836","intvolume":"       996","article_number":"129","external_id":{"arxiv":["2509.05434"]},"tmp":{"legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","short":"CC BY (4.0)","image":"/images/cc_by.png"},"file":[{"creator":"dernst","file_size":684400,"date_created":"2026-05-04T11:19:48Z","checksum":"7b3cb025d4bcaa35c6e52bd0c8fb6cf4","access_level":"open_access","relation":"main_file","file_name":"2026_AstrophysicalJour_Greene.pdf","content_type":"application/pdf","file_id":"21792","success":1,"date_updated":"2026-05-04T11:19:48Z"}],"fulldoi":"https://doi.org/10.3847/1538-4357/ae1836","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.”","language":[{"iso":"eng"}],"arxiv":1,"date_published":"2026-01-10T00:00:00Z","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."}],"department":[{"_id":"JoMa"}],"PlanS_conform":"1","publication_identifier":{"eissn":["1538-4357"],"issn":["0004-637X"]},"oa_version":"Published Version","publisher":"IOP Publishing","date_updated":"2026-05-04T11:20:42Z","has_accepted_license":"1","volume":996,"year":"2026","publication_status":"published","DOAJ_listed":"1","author":[{"full_name":"Greene, Jenny E.","last_name":"Greene","first_name":"Jenny E."},{"first_name":"David J.","last_name":"Setton","full_name":"Setton, 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."},{"last_name":"Volonteri","full_name":"Volonteri, Marta","first_name":"Marta"},{"first_name":"Pratika","last_name":"Dayal","full_name":"Dayal, Pratika"},{"first_name":"Ivo","full_name":"Labbe, Ivo","last_name":"Labbe"},{"last_name":"Van Dokkum","full_name":"Van Dokkum, Pieter","first_name":"Pieter"},{"first_name":"Rachel","last_name":"Bezanson","full_name":"Bezanson, Rachel"},{"full_name":"Brammer, Gabriel","last_name":"Brammer","first_name":"Gabriel"},{"first_name":"Sam E.","last_name":"Cutler","full_name":"Cutler, Sam E."},{"full_name":"Glazebrook, Karl","last_name":"Glazebrook","first_name":"Karl"},{"first_name":"Anna","full_name":"De Graaff, Anna","last_name":"De Graaff"},{"last_name":"Hirschmann","full_name":"Hirschmann, Michaela","first_name":"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"},{"first_name":"Hanpu","full_name":"Liu, Hanpu","last_name":"Liu"},{"full_name":"Ma, Yilun","last_name":"Ma","first_name":"Yilun"},{"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":"Nanayakkara, Themiya","last_name":"Nanayakkara","first_name":"Themiya"},{"first_name":"Pascal A.","full_name":"Oesch, Pascal A.","last_name":"Oesch"},{"first_name":"Richard","full_name":"Pan, Richard","last_name":"Pan"},{"first_name":"Sedona H.","last_name":"Price","full_name":"Price, Sedona H."},{"first_name":"Justin S.","last_name":"Spilker","full_name":"Spilker, Justin S."},{"first_name":"Bingjie","full_name":"Wang, Bingjie","last_name":"Wang"},{"first_name":"John R.","full_name":"Weaver, John R.","last_name":"Weaver"},{"full_name":"Whitaker, Katherine E.","last_name":"Whitaker","first_name":"Katherine E."},{"first_name":"Christina C.","last_name":"Williams","full_name":"Williams, Christina C."},{"full_name":"Zitrin, Adi","last_name":"Zitrin","first_name":"Adi"}],"scopus_import":"1","OA_place":"publisher"},{"file":[{"creator":"dernst","file_size":19310053,"relation":"main_file","checksum":"65a8237a519188af83b6dc4d47ad85fa","access_level":"open_access","date_created":"2026-04-13T08:36:50Z","file_name":"2026_AstrophysicalJournal_Miller.pdf","content_type":"application/pdf","date_updated":"2026-04-13T08:36:50Z","file_id":"21733","success":1}],"external_id":{"arxiv":["2510.24877"]},"tmp":{"legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","short":"CC BY (4.0)","image":"/images/cc_by.png"},"date_published":"2026-01-01T00:00:00Z","department":[{"_id":"IlCa"}],"abstract":[{"text":"The initial–final mass relation (IFMR) links a star’s birth mass to the mass of its white dwarf (WD) remnant, providing key constraints on stellar evolution. Open clusters offer the most straightforward way to empirically determine the IFMR, as their well-defined ages allow for direct progenitor lifetime estimates. We construct the most comprehensive open cluster WD IFMR to date by combining new spectroscopy of 22 WDs with an extensive literature review of WDs with strong cluster associations. To minimize systematics, we restrict our analysis to spectroscopically confirmed hydrogen-atmosphere (DA) WDs consistent with single-stellar origins. We separately analyze a subset with reliable Gaia-based astrometric membership assessments, as well as a full sample that adds WDs with strong cluster associations whose membership cannot be reliably assessed with Gaia. The Gaia-based sample includes 69 spectroscopically confirmed DA WDs, more than doubling the sample size of previous Gaia-based open cluster IFMRs. The full sample, which includes 53 additional literature WDs,\r\nincreases the total number of cluster WDs by over 50% relative to earlier works. We provide functional forms for both the Gaia-based and full-sample IFMRs. The Gaia-based result useful for Mi � 2.67 M⊙ is Mf = [0.179 0.100H (Mi 3.84 M )] × (Mi 3.84 M ) + 0.628 M , where H(x) is the Heaviside step function. Comparing our IFMR to recent literature, we identify significant deviations from best-fit IFMRs derived from both Gaia-based volume-limited samples of field WDs and double WD binaries, with the largest discrepancy occurring for initial masses of about 5 M⊙.","lang":"eng"}],"fulldoi":"https://doi.org/10.3847/1538-4357/ae18c8","arxiv":1,"acknowledgement":"The authors would like to thank the anonymous referee for their constructive feedback, which helped improve the clarify of the manuscript. This work was supported in part by the Natural Sciences and Engineering Research Council of Canada Discovery grants Nos. DG-RGPIN-2022-03051 and DG-RGPIN-2023-04486. This research received funding from the European Research Council under the European Union’s Horizon 2020 research and innovation program number 101002408 (MOS100PC). This work includes results based on observations obtained at the international Gemini Observatory, a program of NSF’s NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation on behalf of the Gemini Observatory partnership: the National Science Foundation (United States), National Research Council (Canada), Agencia Nacional de Investigación y Desarrollo (Chile), Ministerio de Ciencia, Tecnología e Innovación (Argentina), Ministério da Ciência, Tecnologia, Inovações e Comunicações (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea). This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Gemini spectra were processed using the DRAGONS package (K. Labrie et al. 2023). LRIS spectra were reduced using the Lpipe pipeline (D. A. Perley 2019).\r\n\r\nFacilities: Gaia - (DR2 & DR3), Gemini:Gillett - Gillett Gemini North Telescope (GMOS-N), Gemini:South - Gemini South Telescope (GMOS-S), Keck:I - KECK I Telescope (LRIS).\r\n\r\nSoftware: Astropy (Astropy Collaboration et al. 2013,2018, 2022), emcee (D. Foreman-Mackey et al. 2013).","language":[{"iso":"eng"}],"oa_version":"Published Version","PlanS_conform":"1","publication_identifier":{"eissn":["1538-4357"],"issn":["0004-637X"]},"DOAJ_listed":"1","publication_status":"published","scopus_import":"1","OA_place":"publisher","author":[{"first_name":"David R.","last_name":"Miller","full_name":"Miller, David R."},{"last_name":"Caiazzo","full_name":"Caiazzo, Ilaria","orcid":"0000-0002-4770-5388","first_name":"Ilaria","id":"8ae5b6e7-2a03-11ee-914d-b58ed7a3b47d"},{"full_name":"Heyl, Jeremy","last_name":"Heyl","first_name":"Jeremy"},{"full_name":"Richer, Harvey B.","last_name":"Richer","first_name":"Harvey B."},{"full_name":"Hollands, Mark A.","last_name":"Hollands","first_name":"Mark A."},{"full_name":"Tremblay, Pier Emmanuel","last_name":"Tremblay","first_name":"Pier Emmanuel"},{"first_name":"Kareem","last_name":"El-Badry","full_name":"El-Badry, Kareem"},{"full_name":"Rodriguez, Antonio C.","last_name":"Rodriguez","first_name":"Antonio C."},{"full_name":"Vanderbosch, Zachary P.","last_name":"Vanderbosch","first_name":"Zachary P."}],"has_accepted_license":"1","date_updated":"2026-04-13T08:39:39Z","publisher":"IOP Publishing","year":"2026","volume":996,"user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","title":"The White Dwarf initial–final mass relation from open clusters in Gaia DR3","keyword":["White dwarf stars","Open star clusters","Compact objects","Stellar evolution"],"date_created":"2026-04-12T22:01:52Z","file_date_updated":"2026-04-13T08:36:50Z","publication":"The Astrophysical Journal","_id":"21725","article_type":"original","day":"01","quality_controlled":"1","oa":1,"status":"public","month":"01","OA_type":"gold","citation":{"ama":"Miller DR, Caiazzo I, Heyl J, et al. The White Dwarf initial–final mass relation from open clusters in Gaia DR3. <i>The Astrophysical Journal</i>. 2026;996(1). doi:<a href=\"https://doi.org/10.3847/1538-4357/ae18c8\">10.3847/1538-4357/ae18c8</a>","ista":"Miller DR, Caiazzo I, Heyl J, Richer HB, Hollands MA, Tremblay PE, El-Badry K, Rodriguez AC, Vanderbosch ZP. 2026. The White Dwarf initial–final mass relation from open clusters in Gaia DR3. The Astrophysical Journal. 996(1), 69.","chicago":"Miller, David R., Ilaria Caiazzo, Jeremy Heyl, Harvey B. Richer, Mark A. Hollands, Pier Emmanuel Tremblay, Kareem El-Badry, Antonio C. Rodriguez, and Zachary P. Vanderbosch. “The White Dwarf Initial–Final Mass Relation from Open Clusters in Gaia DR3.” <i>The Astrophysical Journal</i>. IOP Publishing, 2026. <a href=\"https://doi.org/10.3847/1538-4357/ae18c8\">https://doi.org/10.3847/1538-4357/ae18c8</a>.","short":"D.R. Miller, I. Caiazzo, J. Heyl, H.B. Richer, M.A. Hollands, P.E. Tremblay, K. El-Badry, A.C. Rodriguez, Z.P. Vanderbosch, The Astrophysical Journal 996 (2026).","apa":"Miller, D. R., Caiazzo, I., Heyl, J., Richer, H. B., Hollands, M. A., Tremblay, P. E., … Vanderbosch, Z. P. (2026). The White Dwarf initial–final mass relation from open clusters in Gaia DR3. <i>The Astrophysical Journal</i>. IOP Publishing. <a href=\"https://doi.org/10.3847/1538-4357/ae18c8\">https://doi.org/10.3847/1538-4357/ae18c8</a>","ieee":"D. R. Miller <i>et al.</i>, “The White Dwarf initial–final mass relation from open clusters in Gaia DR3,” <i>The Astrophysical Journal</i>, vol. 996, no. 1. IOP Publishing, 2026.","mla":"Miller, David R., et al. “The White Dwarf Initial–Final Mass Relation from Open Clusters in Gaia DR3.” <i>The Astrophysical Journal</i>, vol. 996, no. 1, 69, IOP Publishing, 2026, doi:<a href=\"https://doi.org/10.3847/1538-4357/ae18c8\">10.3847/1538-4357/ae18c8</a>."},"issue":"1","type":"journal_article","intvolume":"       996","article_number":"69","doi":"10.3847/1538-4357/ae18c8","ddc":["520"],"article_processing_charge":"Yes"},{"tmp":{"legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","short":"CC BY (4.0)","image":"/images/cc_by.png"},"external_id":{"arxiv":["2509.07678"]},"file":[{"file_name":"2026_AstrophysicalJournal_PerezCouto.pdf","relation":"main_file","access_level":"open_access","checksum":"c3daf49261a9933c079854c38eec316f","date_created":"2026-04-28T13:06:00Z","file_id":"21773","date_updated":"2026-04-28T13:06:00Z","success":1,"content_type":"application/pdf","creator":"dernst","file_size":2905627}],"acknowledgement":"We thank the anonymous referee for a careful reading of the manuscript and for constructive comments that improved the paper. X.P.C. and S.T. thank J.L. Gragera-Más and Ylva Götberg for their valuable feedback and comments. X.P.C. acknowledges financial support from the Spanish National Programme for the Promotion of Talent and its Employability grant PRE2022-104959 cofunded by the European Social Fund. S.T. acknowledges the funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No. 101034413. E.V. acknowledges support from the DISCOBOLO project funded by the Spanish Ministerio de Ciencia, Innovación y Universidades under grant PID2021-127289NB-I00. A.J.M. acknowledges support from the Swedish National Space Agency (Career grant 2023-00146). X.P.C. and M.M. acknowledge support from the Spanish Ministerio de Ciencia, Innovaciòn y Universidades under grants PID2021122842OB-C22 and PID2024-157964OB-C22; from the Xunta de Galicia and the European Union (FEDER Galicia 2021-2027 Program) Ref. ED431B 2024/21, ED431B 2024/02, and CITIC ED431G 2023/01. This work has made use of data from the European Space Agency (ESA) Gaia mission and processed by the Gaia Data Processing and Analysis Consortium (DPAC). Funding for the DPAC has been provided by national institutions, particularly the institutions participating in the Gaia Multilateral Agreement.","arxiv":1,"language":[{"iso":"eng"}],"fulldoi":"https://doi.org/10.3847/1538-4357/ae56ff","department":[{"_id":"LiBu"}],"abstract":[{"text":"3I/ATLAS is the third interstellar object discovered to date, following 1I/‘Oumuamua and 2I/Borisov. Its unusually high excess velocity and active cometary nature make it a key probe of the Galactic population of icy planetesimals. Understanding its origin requires its past trajectory through the Galaxy to be traced and the possible role of stellar encounters to be assessed, both as a potential origin and a perturber to its orbit. We integrated the orbit of 3I/ATLAS backward in time for 10 Myr, together with a sample of Gaia DR3 stars with high-quality astrometry and radial velocities, to identify close passages within 2 pc. We identify 93 nominal encounters, 62 of which are significant at the 2σ level. However, none of these encounters produced any meaningful perturbation. The strongest perturber Gaia DR3 6863591389529611264 at 0.30 pc and with a relative velocity of 35 km s−1, imparted only a velocity change of ∣Δv∣  ≃  5  ×  10−4 km s−1 to the orbit of 3I/ATLAS. Our results indicate that no stellar flybys within the past 10 Myr and 500 pc contained in Gaia DR3 can account for the present trajectory of 3I/ATLAS or be associated with its origin. We further show that 3I/ATLAS is kinematically consistent with a thin-disk population, despite its large peculiar velocity.","lang":"eng"}],"date_published":"2026-04-20T00:00:00Z","publication_identifier":{"eissn":["1538-4357"],"issn":["0004-637X"]},"PlanS_conform":"1","oa_version":"Published Version","year":"2026","volume":1001,"has_accepted_license":"1","date_updated":"2026-04-28T13:08:39Z","publisher":"IOP Publishing","OA_place":"publisher","scopus_import":"1","author":[{"first_name":"X.","full_name":"Pérez-Couto, X.","last_name":"Pérez-Couto"},{"orcid":"0000-0002-3150-8988","full_name":"Torres Rodriguez, Santiago","last_name":"Torres Rodriguez","id":"a8df4360-4328-11ee-8f1a-e502d0c83fc2","first_name":"Santiago"},{"full_name":"Villaver, E.","last_name":"Villaver","first_name":"E."},{"full_name":"Mustill, A. J.","last_name":"Mustill","first_name":"A. J."},{"last_name":"Manteiga","full_name":"Manteiga, M.","first_name":"M."}],"DOAJ_listed":"1","publication_status":"published","title":"3I/ATLAS: In search of the witnesses to its voyage","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","article_type":"original","quality_controlled":"1","day":"20","oa":1,"project":[{"grant_number":"101034413","call_identifier":"H2020","_id":"fc2ed2f7-9c52-11eb-aca3-c01059dda49c","name":"IST-BRIDGE: International postdoctoral program"}],"file_date_updated":"2026-04-28T13:06:00Z","date_created":"2026-04-26T22:01:46Z","_id":"21760","publication":"The Astrophysical Journal","type":"journal_article","issue":"2","month":"04","citation":{"apa":"Pérez-Couto, X., Torres Rodriguez, S., Villaver, E., Mustill, A. J., &#38; Manteiga, M. (2026). 3I/ATLAS: In search of the witnesses to its voyage. <i>The Astrophysical Journal</i>. IOP Publishing. <a href=\"https://doi.org/10.3847/1538-4357/ae56ff\">https://doi.org/10.3847/1538-4357/ae56ff</a>","mla":"Pérez-Couto, X., et al. “3I/ATLAS: In Search of the Witnesses to Its Voyage.” <i>The Astrophysical Journal</i>, vol. 1001, no. 2, 146, IOP Publishing, 2026, doi:<a href=\"https://doi.org/10.3847/1538-4357/ae56ff\">10.3847/1538-4357/ae56ff</a>.","ieee":"X. Pérez-Couto, S. Torres Rodriguez, E. Villaver, A. J. Mustill, and M. Manteiga, “3I/ATLAS: In search of the witnesses to its voyage,” <i>The Astrophysical Journal</i>, vol. 1001, no. 2. IOP Publishing, 2026.","ama":"Pérez-Couto X, Torres Rodriguez S, Villaver E, Mustill AJ, Manteiga M. 3I/ATLAS: In search of the witnesses to its voyage. <i>The Astrophysical Journal</i>. 2026;1001(2). doi:<a href=\"https://doi.org/10.3847/1538-4357/ae56ff\">10.3847/1538-4357/ae56ff</a>","ista":"Pérez-Couto X, Torres Rodriguez S, Villaver E, Mustill AJ, Manteiga M. 2026. 3I/ATLAS: In search of the witnesses to its voyage. The Astrophysical Journal. 1001(2), 146.","chicago":"Pérez-Couto, X., Santiago Torres Rodriguez, E. Villaver, A. J. Mustill, and M. Manteiga. “3I/ATLAS: In Search of the Witnesses to Its Voyage.” <i>The Astrophysical Journal</i>. IOP Publishing, 2026. <a href=\"https://doi.org/10.3847/1538-4357/ae56ff\">https://doi.org/10.3847/1538-4357/ae56ff</a>.","short":"X. Pérez-Couto, S. Torres Rodriguez, E. Villaver, A.J. Mustill, M. Manteiga, The Astrophysical Journal 1001 (2026)."},"status":"public","OA_type":"gold","article_processing_charge":"Yes","ddc":["520"],"doi":"10.3847/1538-4357/ae56ff","article_number":"146","ec_funded":1,"intvolume":"      1001"},{"oa_version":"Published Version","publication_identifier":{"eissn":["1538-4357"],"issn":["0004-637X"]},"PlanS_conform":"1","OA_place":"publisher","scopus_import":"1","author":[{"first_name":"Kohei","full_name":"Inayoshi, Kohei","last_name":"Inayoshi"},{"last_name":"Shangguan","full_name":"Shangguan, Jinyi","first_name":"Jinyi"},{"full_name":"Chen, Xian","last_name":"Chen","first_name":"Xian"},{"first_name":"Luis C.","full_name":"Ho, Luis C.","last_name":"Ho"},{"first_name":"Zoltán","id":"7c006e8c-cc0d-11ee-8322-cb904ef76f36","last_name":"Haiman","full_name":"Haiman, Zoltán","orcid":"0000-0003-3633-5403"}],"DOAJ_listed":"1","publication_status":"published","year":"2026","volume":1002,"date_updated":"2026-05-11T07:09:12Z","has_accepted_license":"1","publisher":"IOP Publishing","file":[{"content_type":"application/pdf","file_id":"21853","date_updated":"2026-05-11T07:07:22Z","success":1,"checksum":"b4506dfef3dd6da335775071d8f2a0a6","access_level":"open_access","date_created":"2026-05-11T07:07:22Z","relation":"main_file","file_name":"2026_AstrophysicalJour_Inayoshi.pdf","file_size":3041897,"creator":"dernst"}],"tmp":{"legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","short":"CC BY (4.0)","image":"/images/cc_by.png"},"external_id":{"arxiv":["2505.05322"]},"department":[{"_id":"ZoHa"}],"abstract":[{"text":"Little red dots (LRDs) are a newly identified class of broad-line active galactic nuclei (AGNs) with a distinctive V-shaped spectrum characterized by red optical and blue UV continuum emission. Their high abundance at redshifts of z ∼ 6–8 and decline at lower redshifts suggest a transient origin. We propose that the spectral shape of LRDs originates from compact binary black hole systems, in which each black hole is surrounded by a mini-disk and embedded within a larger circumbinary disk. With a binary separation of ≲103 Schwarzschild radii, the Wien tail of a T ≃ 5000 K blackbody spectrum at the inner edge of the circumbinary disk produces the red optical emission, while the mini-disks power the UV continuum. Binary torques carve out a gap between the circumbinary disk and the mini-disks, setting the turnover wavelength of the V-shaped spectrum around the Balmer limit. This scenario naturally reproduces LRD spectra requiring only modest dust attenuation (AV ≲ 1 mag), resolving overestimated luminosities for LRDs in previous studies and alleviating a tension with the so-called Sołtan argument. This model predicts distinct spectral evolution as the binary orbit decays through binary disk interactions and gravitational-wave (GW) emission, linking early-stage “proto-LRD” binaries to the broader AGN population and late-stage “LRD descendants” to coalescing binaries detectable in GW experiments.","lang":"eng"}],"date_published":"2026-05-01T00:00:00Z","acknowledgement":"We greatly thank Kenta Hotokezaka and Hanpu Liu for constructive discussions. K.I., J.S., X.C., and L.C.H. acknowledge support from National Natural Science Foundation of China (grant Nos. 12573015, 1251101148, 12233001, and 12473037), the Beijing Natural Science Foundation (grant No. IS25003), and the China Manned Space Program (grant No. CMS-CSST-2025-A09). J.S. is also supported by “The Fundamental Research Funds for the Central Universities, Peking University” (grant No. 7100604896). Z.H. acknowledges support by US NSF grant AST-2006176 and by NASA grant Nos. 80NSSC24K0440 and 80NSSC22K0822.","language":[{"iso":"eng"}],"arxiv":1,"fulldoi":"https://doi.org/10.3847/1538-4357/ae548d","OA_type":"gold","month":"05","status":"public","citation":{"short":"K. Inayoshi, J. Shangguan, X. Chen, L.C. Ho, Z. Haiman, The Astrophysical Journal 1002 (2026).","chicago":"Inayoshi, Kohei, Jinyi Shangguan, Xian Chen, Luis C. Ho, and Zoltán Haiman. “The Emergence of Little Red Dots from Binary Massive Black Holes.” <i>The Astrophysical Journal</i>. IOP Publishing, 2026. <a href=\"https://doi.org/10.3847/1538-4357/ae548d\">https://doi.org/10.3847/1538-4357/ae548d</a>.","ama":"Inayoshi K, Shangguan J, Chen X, Ho LC, Haiman Z. The emergence of Little Red Dots from binary massive black holes. <i>The Astrophysical Journal</i>. 2026;1002(1). doi:<a href=\"https://doi.org/10.3847/1538-4357/ae548d\">10.3847/1538-4357/ae548d</a>","ista":"Inayoshi K, Shangguan J, Chen X, Ho LC, Haiman Z. 2026. The emergence of Little Red Dots from binary massive black holes. The Astrophysical Journal. 1002(1), 25.","ieee":"K. Inayoshi, J. Shangguan, X. Chen, L. C. Ho, and Z. Haiman, “The emergence of Little Red Dots from binary massive black holes,” <i>The Astrophysical Journal</i>, vol. 1002, no. 1. IOP Publishing, 2026.","mla":"Inayoshi, Kohei, et al. “The Emergence of Little Red Dots from Binary Massive Black Holes.” <i>The Astrophysical Journal</i>, vol. 1002, no. 1, 25, IOP Publishing, 2026, doi:<a href=\"https://doi.org/10.3847/1538-4357/ae548d\">10.3847/1538-4357/ae548d</a>.","apa":"Inayoshi, K., Shangguan, J., Chen, X., Ho, L. C., &#38; Haiman, Z. (2026). The emergence of Little Red Dots from binary massive black holes. <i>The Astrophysical Journal</i>. IOP Publishing. <a href=\"https://doi.org/10.3847/1538-4357/ae548d\">https://doi.org/10.3847/1538-4357/ae548d</a>"},"type":"journal_article","issue":"1","intvolume":"      1002","article_number":"25","doi":"10.3847/1538-4357/ae548d","article_processing_charge":"Yes","ddc":["520"],"user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","title":"The emergence of Little Red Dots from binary massive black holes","file_date_updated":"2026-05-11T07:07:22Z","date_created":"2026-05-10T22:02:14Z","_id":"21844","publication":"The Astrophysical Journal","day":"01","article_type":"original","quality_controlled":"1","oa":1},{"PlanS_conform":"1","publication_identifier":{"eissn":["1538-4357"],"issn":["0004-637X"]},"oa_version":"Published Version","publisher":"IOP Publishing","has_accepted_license":"1","date_updated":"2026-05-18T08:18:39Z","volume":1003,"year":"2026","publication_status":"published","DOAJ_listed":"1","author":[{"first_name":"Bingjie","last_name":"Wang","full_name":"Wang, Bingjie"},{"last_name":"Leja","full_name":"Leja, Joel","first_name":"Joel"},{"last_name":"Katz","full_name":"Katz, Harley","first_name":"Harley"},{"last_name":"Inayoshi","full_name":"Inayoshi, Kohei","first_name":"Kohei"},{"last_name":"Cleri","full_name":"Cleri, Nikko J.","first_name":"Nikko J."},{"full_name":"De Graaff, Anna","last_name":"De Graaff","first_name":"Anna"},{"full_name":"Hviding, Raphael E.","last_name":"Hviding","first_name":"Raphael E."},{"last_name":"Van Dokkum","full_name":"Van Dokkum, Pieter","first_name":"Pieter"},{"first_name":"Jenny E.","last_name":"Greene","full_name":"Greene, Jenny E."},{"last_name":"Labbé","full_name":"Labbé, Ivo","first_name":"Ivo"},{"id":"7439a258-f3c0-11ec-9501-9df22fe06720","first_name":"Jorryt J","orcid":"0000-0003-2871-127X","full_name":"Matthee, Jorryt J","last_name":"Matthee"},{"first_name":"Ian","full_name":"Mcconachie, Ian","last_name":"Mcconachie"},{"first_name":"Rohan P.","full_name":"Naidu, Rohan P.","last_name":"Naidu"},{"last_name":"Nelson","full_name":"Nelson, Erica J.","first_name":"Erica J."}],"scopus_import":"1","OA_place":"publisher","external_id":{"arxiv":["2508.18358"]},"tmp":{"legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","short":"CC BY (4.0)","image":"/images/cc_by.png"},"file":[{"file_size":2584417,"creator":"dernst","date_updated":"2026-05-18T08:17:26Z","file_id":"21891","success":1,"content_type":"application/pdf","file_name":"2026_AstrophysicalJourn_Wang.pdf","access_level":"open_access","date_created":"2026-05-18T08:17:26Z","checksum":"ee9ebc8ae2304fec04f24b82ebaac8bc","relation":"main_file"}],"fulldoi":"https://doi.org/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.","language":[{"iso":"eng"}],"arxiv":1,"date_published":"2026-05-01T00:00:00Z","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."}],"department":[{"_id":"JoMa"}],"issue":"1","type":"journal_article","citation":{"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>.","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>","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.","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.","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>"},"month":"05","OA_type":"gold","status":"public","ddc":["520"],"article_processing_charge":"Yes","doi":"10.3847/1538-4357/ae5bab","intvolume":"      1003","article_number":"10","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","title":"The missing hard photons of Little Red Dots: Their incident ionizing spectra resemble massive stars","oa":1,"quality_controlled":"1","article_type":"original","day":"01","publication":"The Astrophysical Journal","_id":"21882","date_created":"2026-05-17T22:02:10Z","file_date_updated":"2026-05-18T08:17:26Z"},{"OA_place":"publisher","scopus_import":"1","author":[{"first_name":"Danielle A.","full_name":"Berg, Danielle A.","last_name":"Berg"},{"first_name":"Rohan P.","last_name":"Naidu","full_name":"Naidu, Rohan P."},{"last_name":"Chisholm","full_name":"Chisholm, John","first_name":"John"},{"last_name":"Atek","full_name":"Atek, Hakim","first_name":"Hakim"},{"first_name":"Seiji","full_name":"Fujimoto, Seiji","last_name":"Fujimoto"},{"last_name":"Kokorev","full_name":"Kokorev, Vasily","first_name":"Vasily"},{"first_name":"Lukas J.","full_name":"Furtak, Lukas J.","last_name":"Furtak"},{"last_name":"Kobayashi","full_name":"Kobayashi, Chiaki","first_name":"Chiaki"},{"first_name":"Daniel","full_name":"Schaerer, Daniel","last_name":"Schaerer"},{"last_name":"Adamo","full_name":"Adamo, Angela","first_name":"Angela"},{"full_name":"Fei, Qinyue","last_name":"Fei","first_name":"Qinyue"},{"full_name":"Korber, Damien","last_name":"Korber","first_name":"Damien"},{"first_name":"Jorryt J","id":"7439a258-f3c0-11ec-9501-9df22fe06720","last_name":"Matthee","full_name":"Matthee, Jorryt J","orcid":"0000-0003-2871-127X"},{"full_name":"Marques-Chaves, Rui","last_name":"Marques-Chaves","first_name":"Rui"},{"full_name":"Martinez, Zorayda","last_name":"Martinez","first_name":"Zorayda"},{"full_name":"Mcquinn, Kristen B.W.","last_name":"Mcquinn","first_name":"Kristen B.W."},{"first_name":"Julian B.","last_name":"Muñoz","full_name":"Muñoz, Julian B."},{"full_name":"Oesch, Pascal A.","last_name":"Oesch","first_name":"Pascal A."},{"first_name":"Alberto","last_name":"Saldana-Lopez","full_name":"Saldana-Lopez, Alberto"},{"first_name":"Daniel P.","full_name":"Stark, Daniel P.","last_name":"Stark"},{"first_name":"Mabel G.","last_name":"Stephenson","full_name":"Stephenson, Mabel G."},{"first_name":"Tiger Yu Yang","full_name":"Hsiao, Tiger Yu Yang","last_name":"Hsiao"}],"DOAJ_listed":"1","publication_status":"published","year":"2026","volume":1003,"date_updated":"2026-06-02T08:46:20Z","has_accepted_license":"1","publisher":"IOP Publishing","oa_version":"Published Version","publication_identifier":{"issn":["0004-637X"],"eissn":["1538-4357"]},"PlanS_conform":"1","department":[{"_id":"JoMa"}],"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."}],"date_published":"2026-05-20T00:00:00Z","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.","arxiv":1,"language":[{"iso":"eng"}],"fulldoi":"https://doi.org/10.3847/1538-4357/ae5e4c","file":[{"file_name":"2026_AstrophysicalJour_Berg.pdf","date_created":"2026-06-02T08:46:08Z","access_level":"open_access","checksum":"1058555fdede45e10fca25d74e7977bc","relation":"main_file","file_id":"21938","date_updated":"2026-06-02T08:46:08Z","success":1,"content_type":"application/pdf","creator":"dernst","file_size":21249354}],"tmp":{"legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","short":"CC BY (4.0)","image":"/images/cc_by.png"},"external_id":{"arxiv":["2511.13591"]},"intvolume":"      1003","doi":"10.3847/1538-4357/ae5e4c","article_number":"112","article_processing_charge":"Yes","ddc":["520"],"citation":{"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>.","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.","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>","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>.","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).","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.","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>"},"month":"05","OA_type":"gold","status":"public","issue":"2","type":"journal_article","file_date_updated":"2026-06-02T08:46:08Z","date_created":"2026-05-31T22:02:12Z","publication":"The Astrophysical Journal","_id":"21930","quality_controlled":"1","article_type":"original","day":"20","oa":1,"title":"A fleeting GLIMPSE of N/O enrichment at cosmic dawn: Evidence for Wolf Rayet N stars in a z = 6.1 galaxy","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87"},{"article_number":"159","doi":"10.3847/1538-4357/ae7bfc","intvolume":"      1005","ddc":["520"],"article_processing_charge":"Yes","status":"public","citation":{"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>","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.","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>.","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>","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.","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).","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>."},"OA_type":"gold","month":"07","issue":"2","type":"journal_article","_id":"22264","publication":"The Astrophysical Journal","file_date_updated":"2026-07-13T07:35:16Z","date_created":"2026-07-12T22:02:17Z","oa":1,"day":"10","quality_controlled":"1","article_type":"original","title":"The mass–metallicity relation and its observational effects at z ∼ 3–6","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","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","keyword":["Galaxy evolution","Chemical enrichment","Metallicity","Galaxy abundances","Scaling relations"],"publication_status":"published","DOAJ_listed":"1","author":[{"full_name":"Lewis, Zach","last_name":"Lewis","first_name":"Zach"},{"first_name":"Michael V.","full_name":"Maseda, Michael V.","last_name":"Maseda"},{"last_name":"De Graaff","full_name":"De Graaff, Anna","first_name":"Anna"},{"last_name":"Leja","full_name":"Leja, Joel","first_name":"Joel"},{"first_name":"Bingjie","full_name":"Wang, Bingjie","last_name":"Wang"},{"full_name":"Rix, Hans Walter","last_name":"Rix","first_name":"Hans Walter"},{"first_name":"Ian","last_name":"Mcconachie","full_name":"Mcconachie, Ian"},{"last_name":"Cleri","full_name":"Cleri, Nikko J.","first_name":"Nikko J."},{"last_name":"Bezanson","full_name":"Bezanson, Rachel","first_name":"Rachel"},{"last_name":"Boogaard","full_name":"Boogaard, Leindert A.","first_name":"Leindert A."},{"first_name":"Gabriel","full_name":"Brammer, Gabriel","last_name":"Brammer"},{"first_name":"Jenny E.","last_name":"Greene","full_name":"Greene, Jenny E."},{"full_name":"Hirschmann, Michaela","last_name":"Hirschmann","first_name":"Michaela"},{"first_name":"Harley","last_name":"Katz","full_name":"Katz, Harley"},{"first_name":"Ivo","last_name":"Labbé","full_name":"Labbé, Ivo"},{"id":"7439a258-f3c0-11ec-9501-9df22fe06720","first_name":"Jorryt J","orcid":"0000-0003-2871-127X","last_name":"Matthee","full_name":"Matthee, Jorryt J"},{"first_name":"Tim B.","last_name":"Miller","full_name":"Miller, Tim B."},{"full_name":"Naidu, Rohan P.","last_name":"Naidu","first_name":"Rohan P."},{"last_name":"Oesch","full_name":"Oesch, Pascal A.","first_name":"Pascal A."},{"last_name":"Setton","full_name":"Setton, David J.","first_name":"David J."},{"last_name":"Suess","full_name":"Suess, Katherine A.","first_name":"Katherine A."},{"last_name":"Weibel","full_name":"Weibel, Andrea","first_name":"Andrea"},{"last_name":"Whitaker","full_name":"Whitaker, Katherine E.","first_name":"Katherine E."},{"first_name":"Christina C.","full_name":"Williams, Christina C.","last_name":"Williams"}],"OA_place":"publisher","scopus_import":"1","supplementarymaterial":"no","publisher":"IOP Publishing","date_updated":"2026-07-13T07:40:41Z","has_accepted_license":"1","volume":1005,"year":"2026","das_tickbox":"1","oa_version":"Published Version","researchdata_availability":"yes","PlanS_conform":"1","publication_identifier":{"eissn":["1538-4357"],"issn":["0004-637X"]},"date_published":"2026-07-10T00:00:00Z","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."}],"department":[{"_id":"JoMa"}],"fulldoi":"https://doi.org/10.3847/1538-4357/ae7bfc","language":[{"iso":"eng"}],"arxiv":1,"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 ","file":[{"file_size":1854628,"creator":"dernst","date_updated":"2026-07-13T07:35:16Z","file_id":"22273","success":1,"content_type":"application/pdf","file_name":"2026_AstrophysicalJour_Lewis.pdf","access_level":"open_access","checksum":"9b13fbbc5e5e921c04676ebc532d9c42","date_created":"2026-07-13T07:35:16Z","relation":"main_file"}],"external_id":{"arxiv":["2512.03134"]},"tmp":{"legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","short":"CC BY (4.0)","image":"/images/cc_by.png"}},{"PlanS_conform":"1","publication_identifier":{"eissn":["1538-4357"],"issn":["0004-637X"]},"researchdata_availability":"yes","oa_version":"Published Version","publisher":"IOP Publishing","date_updated":"2026-07-13T08:16:25Z","has_accepted_license":"1","volume":1005,"das_tickbox":"1","year":"2026","publication_status":"published","DOAJ_listed":"1","author":[{"first_name":"Nils B.","last_name":"De Vries","full_name":"De Vries, Nils B."},{"last_name":"Le Saux","full_name":"Le Saux, Arthur","first_name":"Arthur"},{"full_name":"Baraffe, Isabelle","last_name":"Baraffe","first_name":"Isabelle"},{"first_name":"Thomas","last_name":"Guillet","full_name":"Guillet, Thomas"},{"first_name":"Richard H.D.","full_name":"Townsend, Richard H.D.","last_name":"Townsend"},{"id":"2a1fb1fc-f373-11ef-901a-87cee43a1217","first_name":"Armand","full_name":"Leclerc, Armand","last_name":"Leclerc"},{"first_name":"Adrien","full_name":"Morison, Adrien","last_name":"Morison"}],"OA_place":"publisher","supplementarymaterial":"yes","scopus_import":"1","external_id":{"arxiv":["2606.07125"]},"tmp":{"legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","short":"CC BY (4.0)","image":"/images/cc_by.png"},"file":[{"access_level":"open_access","date_created":"2026-07-13T08:14:01Z","checksum":"d32061d2341bac3adeb404975c6bd59e","relation":"main_file","file_name":"2026_AstrophysicalJour_deVries.pdf","content_type":"application/pdf","success":1,"file_id":"22275","date_updated":"2026-07-13T08:14:01Z","creator":"dernst","file_size":14866194}],"fulldoi":"https://doi.org/10.3847/1538-4357/ae7a3c","arxiv":1,"acknowledgement":"We would like to thank the referee for their careful reading of the manuscript and their constructive comments that helped improve the paper. N.B.V. would like to thank K. Belkacem and J. Philidet for helpful discussions. N.B.V. is supported by STFC grant ST/Y002164/1. A.L.S. acknowledges support from the European Research Council (ERC) under the Horizon Europe program (Synergy grant agreement 101071505: 4D-STAR) from the CNES SOHO-GOLF and PLATO grants at CEA-DAp, and from ATPS (CNRS/INSU). Part of this work was supported by the ERC grant No. 787361-COBOM. R.H.D.T. acknowledges support from NASA grants 80NSSC24K0895 and 80NSSC23K1517, and NSF grant 2407636. A.L. is supported by ERC Starting Grant 101165631 (“Calcifer”). The authors would like to acknowledge the use of the University of Exeter High-Performance Computing (HPC) facility, ISCA, in carrying out this work. This work used the DiRAC Memory Intensive service (Cosma8) at Durham University, managed by the Institute for Computational Cosmology, and the DiRAC Data Intensive service (DIaL3) at the University of Leicester, managed by the University of Leicester Research Computing Service. These facilities are managed on behalf of the STFC DiRAC HPC (www.dirac.ac.uk). The DiRAC services at Durham and Leicester were funded by BEIS, UKRI, and STFC capital funding, and STFC operations grants. The service at Durham received funding from Durham University. DiRAC is part of the UKRI Digital Research Infrastructure.","language":[{"iso":"eng"}],"date_published":"2026-07-10T00:00:00Z","abstract":[{"text":"Mixed modes are observed in many low-mass evolved stars. They provide information about core rotation rates of these stars, which are lower than predicted by stellar evolution models. The mixed modes themselves have been invoked as an angular momentum (AM) transport mechanism, but estimating their transport efficiency requires knowledge of their amplitudes. We constrain, for the first time, the mixed-mode amplitudes in 2D hydrodynamical simulations of a 1.3M⊙ red giant using the code MUSIC. We perform two simulations with outer radial truncations at fractional radii ro/r⋆ = 0.90 and 0.98. We compare the modes in the simulation with those found using both GYRE and a Dedalus eigenvalue solver. Excellent frequency agreement is found for all p-dominated modes, with minor discrepancies for g-dominated modes, especially in the frequency range [60, 240] μHz. We find excellent eigenfunction agreement for all modes except those in this frequency range. According to empirical predictions, the largest kinetic energies are located around Vmax= 312.μHz, but in both simulations, the modes with frequencies of ν < 50 μHz have the largest kinetic energies. In the simulation with r/r⋆ = 0.98, the simulated modes have extrapolated surface velocities comparable to the empirical predictions, with the highest surface velocities in a bell-shaped curve peaking around ν = 700 μHz. The extrapolated surface velocities of the low-frequency modes are small and thus hard to observe, but their large kinetic energies deeper in the interior could significantly impact AM transport, which has not yet been investigated.","lang":"eng"}],"department":[{"_id":"LiBu"}],"issue":"2","type":"journal_article","status":"public","OA_type":"gold","citation":{"apa":"De Vries, N. B., Le Saux, A., Baraffe, I., Guillet, T., Townsend, R. H. D., Leclerc, A., &#38; Morison, A. (2026). Revealing mixed modes in compressible hydrodynamical simulations of red giant stars. <i>The Astrophysical Journal</i>. IOP Publishing. <a href=\"https://doi.org/10.3847/1538-4357/ae7a3c\">https://doi.org/10.3847/1538-4357/ae7a3c</a>","ieee":"N. B. De Vries <i>et al.</i>, “Revealing mixed modes in compressible hydrodynamical simulations of red giant stars,” <i>The Astrophysical Journal</i>, vol. 1005, no. 2. IOP Publishing, 2026.","mla":"De Vries, Nils B., et al. “Revealing Mixed Modes in Compressible Hydrodynamical Simulations of Red Giant Stars.” <i>The Astrophysical Journal</i>, vol. 1005, no. 2, 154, IOP Publishing, 2026, doi:<a href=\"https://doi.org/10.3847/1538-4357/ae7a3c\">10.3847/1538-4357/ae7a3c</a>.","ama":"De Vries NB, Le Saux A, Baraffe I, et al. Revealing mixed modes in compressible hydrodynamical simulations of red giant stars. <i>The Astrophysical Journal</i>. 2026;1005(2). doi:<a href=\"https://doi.org/10.3847/1538-4357/ae7a3c\">10.3847/1538-4357/ae7a3c</a>","ista":"De Vries NB, Le Saux A, Baraffe I, Guillet T, Townsend RHD, Leclerc A, Morison A. 2026. Revealing mixed modes in compressible hydrodynamical simulations of red giant stars. The Astrophysical Journal. 1005(2), 154.","chicago":"De Vries, Nils B., Arthur Le Saux, Isabelle Baraffe, Thomas Guillet, Richard H.D. Townsend, Armand Leclerc, and Adrien Morison. “Revealing Mixed Modes in Compressible Hydrodynamical Simulations of Red Giant Stars.” <i>The Astrophysical Journal</i>. IOP Publishing, 2026. <a href=\"https://doi.org/10.3847/1538-4357/ae7a3c\">https://doi.org/10.3847/1538-4357/ae7a3c</a>.","short":"N.B. De Vries, A. Le Saux, I. Baraffe, T. Guillet, R.H.D. Townsend, A. Leclerc, A. Morison, The Astrophysical Journal 1005 (2026)."},"month":"07","ddc":["520"],"article_processing_charge":"Yes","doi":"10.3847/1538-4357/ae7a3c","article_number":"154","intvolume":"      1005","dataavailabilitystatement":"The kinetic energies and surface velocities shown in Figure 4, as well as the underlying spectral data of this work, can be found in a Zenodo repository at doi:10.5281/zenodo.18661976.","keyword":["Stellar physics","Stellar interiors","Asteroseismology","Stellar oscillations","Hydrodynamical simulations"],"title":"Revealing mixed modes in compressible hydrodynamical simulations of red giant stars","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","project":[{"name":"Unveiling the mysteries of stellar dynamics: a pioneering journey in magnetoasteroseismology","_id":"914d8549-16d5-11f0-9cad-bbe6324c93a9","grant_number":"101165631"}],"oa":1,"day":"10","article_type":"original","quality_controlled":"1","_id":"22262","publication":"The Astrophysical Journal","date_created":"2026-07-12T22:02:17Z","file_date_updated":"2026-07-13T08:14:01Z"},{"oa_version":"Published Version","researchdata_availability":"no","publication_identifier":{"eissn":["1538-4357"],"issn":["0004-637X"]},"author":[{"last_name":"Kokorev","full_name":"Kokorev, Vasily","first_name":"Vasily"},{"first_name":"John","full_name":"Chisholm, John","last_name":"Chisholm"},{"first_name":"Rohan P.","full_name":"Naidu, Rohan P.","last_name":"Naidu"},{"first_name":"Seiji","full_name":"Fujimoto, Seiji","last_name":"Fujimoto"},{"last_name":"Atek","full_name":"Atek, Hakim","first_name":"Hakim"},{"last_name":"Brammer","full_name":"Brammer, Gabriel","first_name":"Gabriel"},{"first_name":"Steven L.","last_name":"Finkelstein","full_name":"Finkelstein, Steven L."},{"full_name":"Akins, Hollis B.","last_name":"Akins","first_name":"Hollis B."},{"last_name":"Berg","full_name":"Berg, Danielle A.","first_name":"Danielle A."},{"full_name":"Furtak, Lukas J.","last_name":"Furtak","first_name":"Lukas J."},{"last_name":"Fei","full_name":"Fei, Qinyue","first_name":"Qinyue"},{"last_name":"Hsiao","full_name":"Hsiao, Tiger Yu-Yang","first_name":"Tiger Yu-Yang"},{"first_name":"Ivo","last_name":"Labbé","full_name":"Labbé, Ivo"},{"first_name":"Jorryt J","id":"7439a258-f3c0-11ec-9501-9df22fe06720","full_name":"Matthee, Jorryt J","last_name":"Matthee","orcid":"0000-0003-2871-127X"},{"full_name":"Muñoz, Julian B.","last_name":"Muñoz","first_name":"Julian B."},{"first_name":"Pascal A.","last_name":"Oesch","full_name":"Oesch, Pascal A."},{"full_name":"Pan, Richard","last_name":"Pan","first_name":"Richard"},{"first_name":"Pierluigi","full_name":"Rinaldi, Pierluigi","last_name":"Rinaldi"},{"first_name":"Alberto","last_name":"Saldana-Lopez","full_name":"Saldana-Lopez, Alberto"},{"last_name":"Schaerer","full_name":"Schaerer, Daniel","first_name":"Daniel"},{"full_name":"Volonteri, Marta","last_name":"Volonteri","first_name":"Marta"},{"full_name":"Zitrin, Adi","last_name":"Zitrin","first_name":"Adi"}],"OA_place":"publisher","supplementarymaterial":"no","scopus_import":"1","publication_status":"published","DOAJ_listed":"1","volume":1004,"das_tickbox":"1","year":"2026","publisher":"IOP Publishing","date_updated":"2026-07-13T13:25:09Z","has_accepted_license":"1","file":[{"file_size":2435643,"creator":"dernst","content_type":"application/pdf","success":1,"date_updated":"2026-07-13T13:23:11Z","file_id":"22313","relation":"main_file","date_created":"2026-07-13T13:23:11Z","checksum":"464e60013bf14d087eb0968e9c81a269","access_level":"open_access","file_name":"2026_AstrophysicalJour_Kokorev.pdf"}],"tmp":{"legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","short":"CC BY (4.0)","image":"/images/cc_by.png"},"external_id":{"arxiv":["2511.07515"]},"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"}],"department":[{"_id":"JoMa"}],"date_published":"2026-06-10T00:00:00Z","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).","language":[{"iso":"eng"}],"arxiv":1,"fulldoi":"https://doi.org/10.3847/1538-4357/ae4ed7","OA_type":"gold","status":"public","month":"06","citation":{"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>","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.","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>.","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>","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>.","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)."},"issue":"2","type":"journal_article","article_number":"153","doi":"10.3847/1538-4357/ae4ed7","intvolume":"      1004","article_processing_charge":"Yes","ddc":["520"],"user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","title":"The Deepest GLIMPSE of a dense gas cocoon enshrouding a Little Red Dot","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).","_id":"22296","publication":"The Astrophysical Journal","file_date_updated":"2026-07-13T13:23:11Z","date_created":"2026-07-13T09:48:38Z","oa":1,"day":"10","article_type":"original","quality_controlled":"1"},{"status":"public","OA_type":"gold","month":"07","citation":{"apa":"Venditti, A., Graziani, L., Schneider, R., Bromm, V., Muñoz, J. B., Di Cesare, C., … Chisholm, J. (2026). Catching the nebular needle in a polluted haystack: Line-emission signatures from population III-forming pockets around massive galaxies at the end of reionization. <i>The Astrophysical Journal</i>. IOP Publishing. <a href=\"https://doi.org/10.3847/1538-4357/ae7b2c\">https://doi.org/10.3847/1538-4357/ae7b2c</a>","mla":"Venditti, Alessandra, et al. “Catching the Nebular Needle in a Polluted Haystack: Line-Emission Signatures from Population III-Forming Pockets around Massive Galaxies at the End of Reionization.” <i>The Astrophysical Journal</i>, vol. 1005, no. 2, 226, IOP Publishing, 2026, doi:<a href=\"https://doi.org/10.3847/1538-4357/ae7b2c\">10.3847/1538-4357/ae7b2c</a>.","ieee":"A. Venditti <i>et al.</i>, “Catching the nebular needle in a polluted haystack: Line-emission signatures from population III-forming pockets around massive galaxies at the end of reionization,” <i>The Astrophysical Journal</i>, vol. 1005, no. 2. IOP Publishing, 2026.","ista":"Venditti A, Graziani L, Schneider R, Bromm V, Muñoz JB, Di Cesare C, Valiante R, Calabrò A, Maiolino R, Finkelstein SL, Parente M, Saggini M, Chisholm J. 2026. Catching the nebular needle in a polluted haystack: Line-emission signatures from population III-forming pockets around massive galaxies at the end of reionization. The Astrophysical Journal. 1005(2), 226.","ama":"Venditti A, Graziani L, Schneider R, et al. Catching the nebular needle in a polluted haystack: Line-emission signatures from population III-forming pockets around massive galaxies at the end of reionization. <i>The Astrophysical Journal</i>. 2026;1005(2). doi:<a href=\"https://doi.org/10.3847/1538-4357/ae7b2c\">10.3847/1538-4357/ae7b2c</a>","short":"A. Venditti, L. Graziani, R. Schneider, V. Bromm, J.B. Muñoz, C. Di Cesare, R. Valiante, A. Calabrò, R. Maiolino, S.L. Finkelstein, M. Parente, M. Saggini, J. Chisholm, The Astrophysical Journal 1005 (2026).","chicago":"Venditti, Alessandra, Luca Graziani, Raffaella Schneider, Volker Bromm, Julian B. Muñoz, Claudia Di Cesare, Rosa Valiante, et al. “Catching the Nebular Needle in a Polluted Haystack: Line-Emission Signatures from Population III-Forming Pockets around Massive Galaxies at the End of Reionization.” <i>The Astrophysical Journal</i>. IOP Publishing, 2026. <a href=\"https://doi.org/10.3847/1538-4357/ae7b2c\">https://doi.org/10.3847/1538-4357/ae7b2c</a>."},"issue":"2","type":"journal_article","intvolume":"      1005","article_number":"226","doi":"10.3847/1538-4357/ae7b2c","article_processing_charge":"Yes","ddc":["520"],"title":"Catching the nebular needle in a polluted haystack: Line-emission signatures from population III-forming pockets around massive galaxies at the end of reionization","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","dataavailabilitystatement":"Software: dustyGadget (L. Graziani et al. 2020), BPASSv2.2.134 (J. J. Eldridge et al. 2017; E. R. Stanway & J. J. Eldridge 2018), Yggdrasil35 (E. Zackrisson et al. 2011), Cloudy22.0136 (G. J. Ferland et al. 2017), NumPy37 (S. van der Walt et al. 2011; C. R. Harris et al. 2020), matplotlib38 (J. D. Hunter 2007), SciPy39 (Jones et al. 2001; P. Virtanen et al. 2020).","publication":"The Astrophysical Journal","_id":"22364","date_created":"2026-07-19T22:01:46Z","file_date_updated":"2026-07-20T13:05:27Z","oa":1,"article_type":"original","day":"10","quality_controlled":"1","project":[{"grant_number":"101076224","_id":"bd9b2118-d553-11ed-ba76-db24564edfea","name":"Young galaxies as tracers and agents of cosmic reionization"}],"oa_version":"Published Version","researchdata_availability":"no","publication_identifier":{"issn":["0004-637X"],"eissn":["1538-4357"]},"PlanS_conform":"1","author":[{"first_name":"Alessandra","last_name":"Venditti","full_name":"Venditti, Alessandra"},{"first_name":"Luca","last_name":"Graziani","full_name":"Graziani, Luca"},{"last_name":"Schneider","full_name":"Schneider, Raffaella","first_name":"Raffaella"},{"first_name":"Volker","full_name":"Bromm, Volker","last_name":"Bromm"},{"first_name":"Julian B.","full_name":"Muñoz, Julian B.","last_name":"Muñoz"},{"last_name":"Di Cesare","full_name":"Di Cesare, Claudia","id":"2d002343-372f-11ef-98ec-a164d20427cb","first_name":"Claudia"},{"full_name":"Valiante, Rosa","last_name":"Valiante","first_name":"Rosa"},{"first_name":"Antonello","last_name":"Calabrò","full_name":"Calabrò, Antonello"},{"first_name":"Roberto","full_name":"Maiolino, Roberto","last_name":"Maiolino"},{"first_name":"Steven L.","last_name":"Finkelstein","full_name":"Finkelstein, Steven L."},{"first_name":"Massimiliano","full_name":"Parente, Massimiliano","last_name":"Parente"},{"last_name":"Saggini","full_name":"Saggini, Matteo","first_name":"Matteo"},{"first_name":"John","full_name":"Chisholm, John","last_name":"Chisholm"}],"OA_place":"publisher","scopus_import":"1","supplementarymaterial":"yes","publication_status":"published","DOAJ_listed":"1","volume":1005,"year":"2026","das_tickbox":"1","publisher":"IOP Publishing","has_accepted_license":"1","date_updated":"2026-07-20T13:07:08Z","file":[{"file_name":"2026_AstrophysicalJour_Venditti.pdf","date_created":"2026-07-20T13:05:27Z","checksum":"e783c9c10cf773482ac2f3b340ad130b","access_level":"open_access","relation":"main_file","date_updated":"2026-07-20T13:05:27Z","success":1,"file_id":"22375","content_type":"application/pdf","creator":"dernst","file_size":2267572}],"tmp":{"legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","short":"CC BY (4.0)","image":"/images/cc_by.png"},"external_id":{"arxiv":["2603.27582"]},"abstract":[{"lang":"eng","text":"Finding the first generation of (Population III or Pop III) stars is one of the most ambitious and exciting challenges of astrophysics. JWST opened concrete prospects for their detection during the Epoch of Reionization, where increasing evidence suggests that residual Pop III formation may persist, even within pristine pockets of high-mass halos, due to inhomogeneous enrichment. However, the identification of Pop III stars within globally enriched environments will be challenging. We investigate the detectability of a subdominant Pop III component in/around massive (M⋆ ≳ 10^9 M⊙) galaxies at z ≈ 6.5–9 from the dustyGadget cosmological simulation suite, and the confusion arising from second-generation (Pop II) stars in their surroundings. We find that young (≲1 Myr), massive (MIII ∼ 6 × 10^5 M⊙) Pop III clusters forming within these galaxy environments are responsible for strong HeII1640 line emission (LHeII1640 ≳ 10^41 erg ^s−1), which would be detectable with ≈10(50) hr of medium-resolution observations with NIRSpec/IFU at z ≈ 6(10). These bright luminosities cannot be produced by standard Pop II populations alone. On the other hand, the dominant Pop II component within massive “hybrid” Pop III hosts powers strong metal line emission (L[OIII]5007 ≳ 10^42 erg s^−1), indicating that the detection of metal lines alone cannot exclude the presence of Pop IIIs in high-z galaxy environments. We further discuss candidate selection strategies based on Lyα, Hα, and Hβ emission, and how spatially resolved observations may enable the detection of isolated, pristine pockets in the outskirts of massive halos."}],"department":[{"_id":"JoMa"}],"date_published":"2026-07-10T00:00:00Z","language":[{"iso":"eng"}],"acknowledgement":"We thank Elka Rusta and Stefania Salvadori for providing predictions of the He II line luminosities from the NEFERTITI model. A.V. acknowledges funding from the Cosmic Frontier Center and the University of Texas at Austin’s College of Natural Sciences. A.V., L.G., and R.S. acknowledge support from the PRIN 2022 MUR project 2022CB3PJ3—First Light And Galaxy aSsembly (FLAGS) funded by the European Union—Next Generation EU. J.B.M. was supported by NSF Grants AST-2307354 and AST-2408637, and by the NSF-Simons AI Institute for Cosmic Origins. This research was also supported in part by grant NSF PHY-2309135 to the Kavli Institute for Theoretical Physics (KITP). R.V. acknowledges support from PRIN MUR “2022935STW” funded by European Union-Next Generation EU, Missione 4 Componente 2 CUP C53D23000950006 and from Bando Ricerca Fondamentale INAF 2023, Theory Grant “Theoretical models for Black Holes Archaeology.\" C.D.C. acknowledges support from the European Union (ERC, AGENTS, 101076224).","arxiv":1,"fulldoi":"https://doi.org/10.3847/1538-4357/ae7b2c"},{"volume":1006,"year":"2026","das_tickbox":"0","publisher":"IOP Publishing","has_accepted_license":"1","date_updated":"2026-08-03T08:00:54Z","author":[{"first_name":"Hiromichi","last_name":"Tagawa","full_name":"Tagawa, Hiromichi"},{"first_name":"Zoltán","id":"7c006e8c-cc0d-11ee-8322-cb904ef76f36","last_name":"Haiman","full_name":"Haiman, Zoltán","orcid":"0000-0003-3633-5403"},{"full_name":"Kimura, Shigeo S.","last_name":"Kimura","first_name":"Shigeo S."},{"full_name":"Yesuf, Hassen M.","last_name":"Yesuf","first_name":"Hassen M."},{"full_name":"Guo, Hengxiao","last_name":"Guo","first_name":"Hengxiao"}],"scopus_import":"1","OA_place":"publisher","supplementarymaterial":"yes","publication_status":"published","DOAJ_listed":"1","publication_identifier":{"eissn":["1538-4357"],"issn":["0004-637X"]},"PlanS_conform":"1","researchdata_availability":"no","oa_version":"Published Version","acknowledgement":"We thank Wen-Biao Han for fruitful discussions on possible scenarios. H.T. is supported by The National Key R&D Program of China (grant No. 2024YFC2207700). S.S.K. was supported by Japan Society for the Promotion of Science (JSPS) KAKENHI grant numbers 22K14028, 21H04487, and 23H04899 and the Tohoku Initiative for Fostering Global Researchers for Interdisciplinary Sciences (TI-FRIS) of MEXT’s Strategic Professional Development Program for Young Researchers. Z.H. was supported by NASA grant 80NSSC22K0822 and NSF grant AST-2006176.","language":[{"iso":"eng"}],"fulldoi":"https://doi.org/10.3847/1538-4357/ae7d29","abstract":[{"text":"Accretion disks in active galactic nuclei (AGN) are promising sites for mergers of stellar-mass black holes (BHs) detectable via gravitational waves (GWs). These environments facilitate both in situ formation and dynamical capture of compact objects and their subsequent mergers. The uncertain origin of GW events detected by LIGO, Virgo, and KAGRA motivates searching for accompanying electromagnetic (EM) signatures. Here, we investigate postmerger EM flares associated with jets launched from merger remnants, as well as from the shocked ambient gas as the jet breaks out of the disk. We find that jet breakout produces luminous gamma-ray emission, detectable with MeV-band telescopes. Cooling emission from a shocked circum-BH minidisk, winds, and background AGN disk peaks in the UV and optical, with durations ranging from about an hour to a month, and can be identified through year-long monitoring of ∼103 AGNs with luminosities ranging from ∼1044 to ∼1045 erg s−1. With a single set of parameters, this postmerger jet model produces gamma-ray, hard X-ray, and optical flares similar to those claimed to be associated with GW events. Furthermore, by incorporating a transition from a high- to low-angular-momentum accretion state after the merger, the model avoids excessive BH growth, alleviating tensions with hyper-Eddington accretion scenarios.","lang":"eng"}],"department":[{"_id":"ZoHa"}],"date_published":"2026-08-01T00:00:00Z","tmp":{"legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","short":"CC BY (4.0)","image":"/images/cc_by.png"},"file":[{"file_size":2873666,"creator":"dernst","content_type":"application/pdf","success":1,"file_id":"22630","date_updated":"2026-08-03T07:58:25Z","access_level":"open_access","date_created":"2026-08-03T07:58:25Z","checksum":"767660c73eb8b0a8bf39f54afe240bc6","relation":"main_file","file_name":"2026_AstrophysicalJournal_Tagawa.pdf"}],"article_processing_charge":"Yes","ddc":["520"],"article_number":"121","doi":"10.3847/1538-4357/ae7d29","intvolume":"      1006","issue":"2","type":"journal_article","status":"public","citation":{"ista":"Tagawa H, Haiman Z, Kimura SS, Yesuf HM, Guo H. 2026. Electromagnetic flares from compact-object mergers in active galactic nucleus disks: Signatures and predictions. The Astrophysical Journal. 1006(2), 121.","ama":"Tagawa H, Haiman Z, Kimura SS, Yesuf HM, Guo H. Electromagnetic flares from compact-object mergers in active galactic nucleus disks: Signatures and predictions. <i>The Astrophysical Journal</i>. 2026;1006(2). doi:<a href=\"https://doi.org/10.3847/1538-4357/ae7d29\">10.3847/1538-4357/ae7d29</a>","short":"H. Tagawa, Z. Haiman, S.S. Kimura, H.M. Yesuf, H. Guo, The Astrophysical Journal 1006 (2026).","chicago":"Tagawa, Hiromichi, Zoltán Haiman, Shigeo S. Kimura, Hassen M. Yesuf, and Hengxiao Guo. “Electromagnetic Flares from Compact-Object Mergers in Active Galactic Nucleus Disks: Signatures and Predictions.” <i>The Astrophysical Journal</i>. IOP Publishing, 2026. <a href=\"https://doi.org/10.3847/1538-4357/ae7d29\">https://doi.org/10.3847/1538-4357/ae7d29</a>.","apa":"Tagawa, H., Haiman, Z., Kimura, S. S., Yesuf, H. M., &#38; Guo, H. (2026). Electromagnetic flares from compact-object mergers in active galactic nucleus disks: Signatures and predictions. <i>The Astrophysical Journal</i>. IOP Publishing. <a href=\"https://doi.org/10.3847/1538-4357/ae7d29\">https://doi.org/10.3847/1538-4357/ae7d29</a>","ieee":"H. Tagawa, Z. Haiman, S. S. Kimura, H. M. Yesuf, and H. Guo, “Electromagnetic flares from compact-object mergers in active galactic nucleus disks: Signatures and predictions,” <i>The Astrophysical Journal</i>, vol. 1006, no. 2. IOP Publishing, 2026.","mla":"Tagawa, Hiromichi, et al. “Electromagnetic Flares from Compact-Object Mergers in Active Galactic Nucleus Disks: Signatures and Predictions.” <i>The Astrophysical Journal</i>, vol. 1006, no. 2, 121, IOP Publishing, 2026, doi:<a href=\"https://doi.org/10.3847/1538-4357/ae7d29\">10.3847/1538-4357/ae7d29</a>."},"month":"08","OA_type":"gold","oa":1,"day":"01","article_type":"original","quality_controlled":"1","_id":"22616","publication":"The Astrophysical Journal","file_date_updated":"2026-08-03T07:58:25Z","date_created":"2026-08-02T22:01:52Z","title":"Electromagnetic flares from compact-object mergers in active galactic nucleus disks: Signatures and predictions","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87"},{"publication_identifier":{"issn":["000-4637X"],"eissn":["1538-4357"]},"PlanS_conform":"1","researchdata_availability":"no","oa_version":"Published Version","year":"2026","das_tickbox":"0","volume":1007,"date_updated":"2026-08-18T09:05:25Z","has_accepted_license":"1","publisher":"IOP Publishing","OA_place":"publisher","supplementarymaterial":"no","scopus_import":"1","author":[{"first_name":"Hiromichi","last_name":"Tagawa","full_name":"Tagawa, Hiromichi"},{"orcid":"0000-0003-3633-5403","last_name":"Haiman","full_name":"Haiman, Zoltán","id":"7c006e8c-cc0d-11ee-8322-cb904ef76f36","first_name":"Zoltán"},{"first_name":"Bence","full_name":"Kocsis, Bence","last_name":"Kocsis"}],"DOAJ_listed":"1","publication_status":"published","tmp":{"legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","short":"CC BY (4.0)","image":"/images/cc_by.png"},"external_id":{"arxiv":["2604.25994"]},"file":[{"file_name":"2026_AstrophysicalJour_Tagawa.pdf","relation":"main_file","access_level":"open_access","checksum":"1531fd5997b054d26e99d44ccc7f8ff5","date_created":"2026-08-18T09:01:50Z","date_updated":"2026-08-18T09:01:50Z","file_id":"22731","success":1,"content_type":"application/pdf","creator":"dernst","file_size":2246236}],"acknowledgement":"H.T. is supported by the National Science and Technology Major Project of China (No. 2024ZD1100601) and the National Key R&D Program of China (grant No.2024YFC2207700). Z.H. was supported by NASA grants 80NSSC22K0822 and 80NSSC24K0440. B.K. is supported by the Science and Technology Facilities Council grant No. ST/W000903/1. Simulations were carried out on Cray XD2000 at the Center for Computational Astrophysics, National Astronomical Observatory of Japan.","language":[{"iso":"eng"}],"arxiv":1,"fulldoi":"https://doi.org/10.3847/1538-4357/ae8760","department":[{"_id":"ZoHa"}],"abstract":[{"lang":"eng","text":"Ground-based gravitational-wave (GW) observatories have detected approximately 200 binary black hole (BH) mergers. The astrophysical origin of these events is debated, with evidence suggesting that at least a subset originated from dynamic environments characterized by frequent close encounters. Accretion disks in active galactic nuclei (AGNs) are of particular interest, as certain observed features could be more readily produced within such environments. In this paper, we investigate the expected properties of mergers in these environments, and their dependence on various parameters, using 1D N-body simulations combined with a comprehensive semianalytical model. In our fiducial model, the distributions of masses (m1 and m2) and mass ratios (q ≡ m2/m1 ≤ 1) are similar to those observed. However, they depend strongly on the lifetime and density of the AGN disk and on the number and accretion efficiency of BHs, with higher masses predicted as these quantities increase. The most massive mergers, such as GW231123, can be produced either by efficient gas accretion or by hierarchical mergers among ≥3 generations of BHs. The observed negative correlation between q and the average effective spin (χeff), along with the positive correlation between χeff and the chirp mass (Mchirp), can be explained by a combination of efficient gas accretion, which promotes spin alignment, and hierarchical mergers, which produce high-∣χeff∣ and low-q binaries. Hierarchical mergers can also explain the negative correlation between q and the dispersion of χeff, as well as the positive correlation between ∣χeff∣and Mchirp. We present a comprehensive study on how the expected distribution of each of these quantities depends on model parameters and assumptions, which will aid the interpretation of observed GW population properties."}],"date_published":"2026-08-10T00:00:00Z","issue":"1","type":"journal_article","citation":{"mla":"Tagawa, Hiromichi, et al. “Properties of Black Hole Mergers in Disks of Active Galactic Nuclei.” <i>The Astrophysical Journal</i>, vol. 1007, no. 1, 67, IOP Publishing, 2026, doi:<a href=\"https://doi.org/10.3847/1538-4357/ae8760\">10.3847/1538-4357/ae8760</a>.","ieee":"H. Tagawa, Z. Haiman, and B. Kocsis, “Properties of black hole mergers in disks of active galactic nuclei,” <i>The Astrophysical Journal</i>, vol. 1007, no. 1. IOP Publishing, 2026.","apa":"Tagawa, H., Haiman, Z., &#38; Kocsis, B. (2026). Properties of black hole mergers in disks of active galactic nuclei. <i>The Astrophysical Journal</i>. IOP Publishing. <a href=\"https://doi.org/10.3847/1538-4357/ae8760\">https://doi.org/10.3847/1538-4357/ae8760</a>","chicago":"Tagawa, Hiromichi, Zoltán Haiman, and Bence Kocsis. “Properties of Black Hole Mergers in Disks of Active Galactic Nuclei.” <i>The Astrophysical Journal</i>. IOP Publishing, 2026. <a href=\"https://doi.org/10.3847/1538-4357/ae8760\">https://doi.org/10.3847/1538-4357/ae8760</a>.","short":"H. Tagawa, Z. Haiman, B. Kocsis, The Astrophysical Journal 1007 (2026).","ama":"Tagawa H, Haiman Z, Kocsis B. Properties of black hole mergers in disks of active galactic nuclei. <i>The Astrophysical Journal</i>. 2026;1007(1). doi:<a href=\"https://doi.org/10.3847/1538-4357/ae8760\">10.3847/1538-4357/ae8760</a>","ista":"Tagawa H, Haiman Z, Kocsis B. 2026. Properties of black hole mergers in disks of active galactic nuclei. The Astrophysical Journal. 1007(1), 67."},"status":"public","OA_type":"gold","month":"08","article_processing_charge":"Yes","ddc":["520"],"article_number":"67","doi":"10.3847/1538-4357/ae8760","intvolume":"      1007","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","title":"Properties of black hole mergers in disks of active galactic nuclei","day":"10","article_type":"original","quality_controlled":"1","oa":1,"file_date_updated":"2026-08-18T09:01:50Z","date_created":"2026-08-16T22:01:43Z","publication":"The Astrophysical Journal","_id":"22713"},{"type":"journal_article","issue":"2","citation":{"mla":"Caputi, Karina I., et al. “Pseudo Little Red Dot: An Active Black Hole Embedded in a Dense and Dusty, Metal-Poor Starburst Galaxy at z = 5.96.” <i>The Astrophysical Journal</i>, vol. 1007, no. 2, 203, IOP Publishing, 2026, doi:<a href=\"https://doi.org/10.3847/1538-4357/ae80b9\">10.3847/1538-4357/ae80b9</a>.","ieee":"K. I. Caputi, R. A. Cooper, P. Rinaldi, R. Navarro-Carrera, E. Iani, and A. A. Tumborang, “Pseudo Little Red Dot: An active black hole embedded in a dense and dusty, metal-poor starburst galaxy at z = 5.96,” <i>The Astrophysical Journal</i>, vol. 1007, no. 2. IOP Publishing, 2026.","apa":"Caputi, K. I., Cooper, R. A., Rinaldi, P., Navarro-Carrera, R., Iani, E., &#38; Tumborang, A. A. (2026). Pseudo Little Red Dot: An active black hole embedded in a dense and dusty, metal-poor starburst galaxy at z = 5.96. <i>The Astrophysical Journal</i>. IOP Publishing. <a href=\"https://doi.org/10.3847/1538-4357/ae80b9\">https://doi.org/10.3847/1538-4357/ae80b9</a>","chicago":"Caputi, Karina I., Ryan A. Cooper, Pierluigi Rinaldi, Rafael Navarro-Carrera, Edoardo Iani, and Abigail A. Tumborang. “Pseudo Little Red Dot: An Active Black Hole Embedded in a Dense and Dusty, Metal-Poor Starburst Galaxy at z = 5.96.” <i>The Astrophysical Journal</i>. IOP Publishing, 2026. <a href=\"https://doi.org/10.3847/1538-4357/ae80b9\">https://doi.org/10.3847/1538-4357/ae80b9</a>.","short":"K.I. Caputi, R.A. Cooper, P. Rinaldi, R. Navarro-Carrera, E. Iani, A.A. Tumborang, The Astrophysical Journal 1007 (2026).","ama":"Caputi KI, Cooper RA, Rinaldi P, Navarro-Carrera R, Iani E, Tumborang AA. Pseudo Little Red Dot: An active black hole embedded in a dense and dusty, metal-poor starburst galaxy at z = 5.96. <i>The Astrophysical Journal</i>. 2026;1007(2). doi:<a href=\"https://doi.org/10.3847/1538-4357/ae80b9\">10.3847/1538-4357/ae80b9</a>","ista":"Caputi KI, Cooper RA, Rinaldi P, Navarro-Carrera R, Iani E, Tumborang AA. 2026. Pseudo Little Red Dot: An active black hole embedded in a dense and dusty, metal-poor starburst galaxy at z = 5.96. The Astrophysical Journal. 1007(2), 203."},"month":"08","OA_type":"gold","status":"public","ddc":["520"],"article_processing_charge":"Yes","article_number":"203","intvolume":"      1007","doi":"10.3847/1538-4357/ae80b9","title":"Pseudo Little Red Dot: An active black hole embedded in a dense and dusty, metal-poor starburst galaxy at z = 5.96","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","day":"20","quality_controlled":"1","article_type":"original","oa":1,"file_date_updated":"2026-09-09T12:19:36Z","date_created":"2026-09-06T22:01:56Z","_id":"22814","publication":"The Astrophysical Journal","publication_identifier":{"issn":["0004-637X"],"eissn":["1538-4357"]},"oa_version":"Published Version","researchdata_availability":"no","has_accepted_license":"1","date_updated":"2026-09-09T12:19:54Z","publisher":"IOP Publishing","year":"2026","das_tickbox":"0","volume":1007,"DOAJ_listed":"1","publication_status":"published","OA_place":"publisher","supplementarymaterial":"no","scopus_import":"1","author":[{"first_name":"Karina I.","full_name":"Caputi, Karina I.","last_name":"Caputi"},{"full_name":"Cooper, Ryan A.","last_name":"Cooper","first_name":"Ryan A."},{"first_name":"Pierluigi","last_name":"Rinaldi","full_name":"Rinaldi, Pierluigi"},{"last_name":"Navarro-Carrera","full_name":"Navarro-Carrera, Rafael","first_name":"Rafael"},{"orcid":"0000-0001-8386-3546","full_name":"Iani, Edoardo","last_name":"Iani","id":"4053390a-6b68-11ef-9828-a3b8adef8d0a","first_name":"Edoardo"},{"full_name":"Tumborang, Abigail A.","last_name":"Tumborang","first_name":"Abigail A."}],"external_id":{"arxiv":["2601.11466"]},"tmp":{"legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","short":"CC BY (4.0)","image":"/images/cc_by.png"},"file":[{"creator":"dernst","file_size":2636477,"file_name":"2026_AstrophysicalJour_Caputi.pdf","relation":"main_file","checksum":"cf878372382ac61b22f679b558bb4e4e","access_level":"open_access","date_created":"2026-09-09T12:19:36Z","date_updated":"2026-09-09T12:19:36Z","file_id":"22887","success":1,"content_type":"application/pdf"}],"fulldoi":"https://doi.org/10.3847/1538-4357/ae80b9","language":[{"iso":"eng"}],"arxiv":1,"acknowledgement":"We are grateful to Daniela Calzetti, Andrea Ferrara, Kohei Inayoshi, Roberto Maiolino, Gabriele Pezzulli, Fengwu Sun, and Z. Yan for useful discussions; José M. Diego for providing us the most updated magnification value for our source; Raphael Hviding for making his Python package unite public and instructing us regarding its use; and Elka Rusta and Stefania Salvadori for providing us their galaxy SED models with hybrid Pop III stellar populations. We also thank the anonymous referee for a useful and constructive report.\r\n\r\nThis work is based on observations made with the NASA/ESA/CSA JWST. 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 the JWST GTO program PID 1208. The specific observations analyzed here can be accessed via doi:10.17909/pyr9-5r43. Some of the analyzed data products 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. This work is also 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 526555.\r\n\r\nK.I.C. and R.N.C. acknowledge funding from the Dutch Research Council (NWO) through the award of the Vici grant VI.C.212.036.","date_published":"2026-08-20T00:00:00Z","department":[{"_id":"JoMa"}],"abstract":[{"text":"We present a study of a pseudo little red dot with no metal lines (Pseudo-LRD-NOM), a highly magnified lowmass galaxy behind the lensing cluster A370 at z = 5.96. We classify this object as a pseudo-LRD because its red\r\nrest-frame optical color is contaminated by a prominent Hα line (with EW0 ≳ 800 Å) present in its JWST\r\nNIRSpec spectrum. Hα is dominated by a narrow component and also has a minor broad component indicative of\r\nan active black hole with MBH ≈ 5.6 × 10^6 M⊙. A narrow Hβ emission line is also detected (where the signal-tonoise ratio, S/N, is 8), producing a Balmer decrement (narrow) Hα/Hβ = 11. The rest-frame UV spectral slope is ßspec/uv = - 1.20 ± 0.28. All these features can be ascribed to high dust attenuation. However, no [O III]λ5007 or\r\nany other metal lines are detected in the spectrum, so [O III]5007/Hβ < 0.25, at odds with a simple dust attenuation explanation. Accounting for all the spectral properties requires the model of a starburst with moderate\r\ncolor excess E(B − V )≈0.2–0.5, high gas density (nH ≳ 10^6 cm^−3\r\n), and low- to extremely-low gas/stellar\r\nmetallicities (Z = 0.01–0.1 Z⊙). The demagnified stellar mass is\r\n× 2.25+\r\n0\r\n1\r\n.\r\n.\r\n8\r\n3\r\n3\r\n0 10^7 M , and the stellar-mass surface\r\ndensity is = +\r\n* 418 M pc 310\r\n725 2, similar to that of massive/nuclear star clusters. Pseudo-LRD-NOM provides\r\nevidence of massive black-hole growth occurring in a high-density, dusty starburst that is at the early stages of its\r\nchemical enrichment, and is likely a precursor to a real LRD.","lang":"eng"}]},{"date_created":"2026-06-14T22:01:42Z","file_date_updated":"2026-06-19T09:56:29Z","publication":"The Astrophysical Journal","_id":"21997","quality_controlled":"1","day":"10","article_type":"original","oa":1,"user_id":"317138e5-6ab7-11ef-aa6d-ffef3953e345","title":"A path to constraints on common envelope ejection in massive binaries: Full evolutionary reconstruction of three Black Hole X-ray binaries","doi":"10.3847/1538-4357/ae66fd","article_number":"31","intvolume":"      1004","article_processing_charge":"Yes","ddc":["520"],"month":"06","citation":{"short":"Z. Li, D. Wei, S. Jia, H. Chen, H. Ge, Z. Chen, Y. Zhang, X. Chen, Z. Han, The Astrophysical Journal 1004 (2026).","chicago":"Li, Zhenwei, Dandan Wei, Shi Jia, Hailiang Chen, Hongwei Ge, Zhuo Chen, Yangyang Zhang, Xuefei Chen, and Zhanwen Han. “A Path to Constraints on Common Envelope Ejection in Massive Binaries: Full Evolutionary Reconstruction of Three Black Hole X-Ray Binaries.” <i>The Astrophysical Journal</i>. IOP Publishing, 2026. <a href=\"https://doi.org/10.3847/1538-4357/ae66fd\">https://doi.org/10.3847/1538-4357/ae66fd</a>.","ama":"Li Z, Wei D, Jia S, et al. A path to constraints on common envelope ejection in massive binaries: Full evolutionary reconstruction of three Black Hole X-ray binaries. <i>The Astrophysical Journal</i>. 2026;1004(1). doi:<a href=\"https://doi.org/10.3847/1538-4357/ae66fd\">10.3847/1538-4357/ae66fd</a>","ista":"Li Z, Wei D, Jia S, Chen H, Ge H, Chen Z, Zhang Y, Chen X, Han Z. 2026. A path to constraints on common envelope ejection in massive binaries: Full evolutionary reconstruction of three Black Hole X-ray binaries. The Astrophysical Journal. 1004(1), 31.","mla":"Li, Zhenwei, et al. “A Path to Constraints on Common Envelope Ejection in Massive Binaries: Full Evolutionary Reconstruction of Three Black Hole X-Ray Binaries.” <i>The Astrophysical Journal</i>, vol. 1004, no. 1, 31, IOP Publishing, 2026, doi:<a href=\"https://doi.org/10.3847/1538-4357/ae66fd\">10.3847/1538-4357/ae66fd</a>.","ieee":"Z. Li <i>et al.</i>, “A path to constraints on common envelope ejection in massive binaries: Full evolutionary reconstruction of three Black Hole X-ray binaries,” <i>The Astrophysical Journal</i>, vol. 1004, no. 1. IOP Publishing, 2026.","apa":"Li, Z., Wei, D., Jia, S., Chen, H., Ge, H., Chen, Z., … Han, Z. (2026). A path to constraints on common envelope ejection in massive binaries: Full evolutionary reconstruction of three Black Hole X-ray binaries. <i>The Astrophysical Journal</i>. IOP Publishing. <a href=\"https://doi.org/10.3847/1538-4357/ae66fd\">https://doi.org/10.3847/1538-4357/ae66fd</a>"},"OA_type":"gold","status":"public","type":"journal_article","issue":"1","department":[{"_id":"YlGo"}],"abstract":[{"lang":"eng","text":"The massive binary common envelope (CE) phase plays a pivotal role in the formation of close black hole (BH)/neutron star binaries, yet significant uncertainties remain in our understanding of this process. In this study, we aim to constrain the massive binary CE phase by systematically reconstructing three observed BH X-ray binaries (BHXBs): GRO J1655-40, SAX J1819.3-2525, and 4U 1543-47. Through comprehensive binary evolution simulations and parametric supernova modeling, we establish lower limits for the CE efficiency parameters under different energy considerations within the standard energy formalism. Specifically, we derive minimum values for three cases: α0.5U and αU, representing CE efficiencies with half and all of the internal energy contributing to the envelope ejection, respectively, and αH, accounting for the envelope’s enthalpy. Our analysis reveals that the self-consistent formation of these three BHXBs requires CE efficiency parameters satisfying α0.5U ≳ 6.7, αU ≳ 4.2, and αH ≳ 1.7. Notably, we find no viable solutions with CE efficiency values below unity, even when considering the most extreme scenarios, in which the envelope binding energy is significantly reduced through enthalpy inclusion. Our results strongly imply that either additional energy sources are required or the formalism itself must be revised. Furthermore, we quantitatively assess the impact of BH natal kicks on our results. A key finding is that 4U 1543-47’s formation requires substantial natal kicks (≳50 km s−1), as lower kick velocities are incompatible with isolated binary evolution."}],"date_published":"2026-06-10T00:00:00Z","arxiv":1,"acknowledgement":"We deeply thank the referee for a very careful reading and constructive comments that have led to the improvement of the manuscript. The authors are grateful to Poshak Gandhi for his valuable suggestions and feedback on this work. This work is supported by the Natural Science Foundation of China (grant Nos. 12125303, 12525304, 12288102, 12473034, 12103028, 12333008, 12422305, 12090040/3, 12273105, 11703081, 11422324, 12073070, and 12173081), the CAS Project for Young Scientists in Basic Research (YSBR-148), the Strategic Priority Research Program of the Chinese Academy of Sciences (grant Nos. XDB1160303, XDB1160201, and XDB1160000), the National Key R&D Program of China (grant Nos. 2021YFA1600403 and 2021YFA1600400), the Key Research Program of Frontier Sciences of CAS (No. ZDBS-LY-7005), the “CAS Light of West China”, the Yunnan Revitalization Talent Support Program-Science & Technology Champion Project (No. 202305AB350003) and Young Talent Project, the International Centre of Supernovae (ICESUN), Yunnan Key Laboratory of Supernova Research (Nos. 202302AN360001 and 202201BC070003), Yunnan Fundamental Research Projects (No. 202401AT070139), and the Natural Science Foundation of Henan Province (No. 242300420944). X.C. acknowledges the New Cornerstone Science Foundation through the XPLORER PRIZE. The authors gratefully acknowledge the “PHOENIX Supercomputing Platform” jointly operated by the Binary Population Synthesis Group and the Stellar Astrophysics Group at Yunnan Observatories, Chinese Academy of Sciences.","language":[{"iso":"eng"}],"fulldoi":"https://doi.org/10.3847/1538-4357/ae66fd","file":[{"content_type":"application/pdf","date_updated":"2026-06-19T09:56:29Z","file_id":"22099","success":1,"relation":"main_file","access_level":"open_access","checksum":"bb76fbb51f8d2834cb79f19e7932e3bd","date_created":"2026-06-19T09:56:29Z","file_name":"2026_AstrophysicalJour_Li.pdf","file_size":3386217,"creator":"dernst"}],"tmp":{"legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","short":"CC BY (4.0)","image":"/images/cc_by.png"},"external_id":{"arxiv":["2604.10440"]},"scopus_import":"1","supplementarymaterial":"no","OA_place":"publisher","author":[{"first_name":"Zhenwei","full_name":"Li, Zhenwei","last_name":"Li"},{"full_name":"Wei, Dandan","last_name":"Wei","id":"5dd129bd-0601-11ef-b325-833284687b76","first_name":"Dandan"},{"first_name":"Shi","last_name":"Jia","full_name":"Jia, Shi"},{"last_name":"Chen","full_name":"Chen, Hailiang","first_name":"Hailiang"},{"full_name":"Ge, Hongwei","last_name":"Ge","first_name":"Hongwei"},{"first_name":"Zhuo","last_name":"Chen","full_name":"Chen, Zhuo"},{"first_name":"Yangyang","last_name":"Zhang","full_name":"Zhang, Yangyang"},{"first_name":"Xuefei","last_name":"Chen","full_name":"Chen, Xuefei"},{"first_name":"Zhanwen","last_name":"Han","full_name":"Han, Zhanwen"}],"DOAJ_listed":"1","publication_status":"published","year":"2026","das_tickbox":"0","volume":1004,"date_updated":"2026-09-16T08:31:10Z","has_accepted_license":"1","publisher":"IOP Publishing","oa_version":"Published Version","researchdata_availability":"no","publication_identifier":{"eissn":["1538-4357"],"issn":["0004-637X"]},"PlanS_conform":"1"},{"OA_type":"gold","status":"public","month":"12","citation":{"chicago":"Setton, David J., Jenny E. Greene, Anna de Graaff, Yilun 逸伦 Ma, Joel Leja, Jorryt J Matthee, Rachel Bezanson, et al. “Little Red Dots at an Inflection Point: Ubiquitous v-Shaped Turnover Consistently Occurs at the Balmer Limit.” <i>The Astrophysical Journal</i>. IOP Publishing, 2025. <a href=\"https://doi.org/10.3847/1538-4357/ae1500\">https://doi.org/10.3847/1538-4357/ae1500</a>.","short":"D.J. Setton, J.E. Greene, A. de Graaff, Y.逸伦 Ma, J. Leja, J.J. Matthee, R. Bezanson, L.A. Boogaard, N.J. Cleri, H. Katz, I. Labbe, M.V. Maseda, I. McConachie, T.B. Miller, S.H. Price, K.A. Suess, P. van Dokkum, B.冰洁 Wang 王, A. Weibel, K.E. Whitaker, C.C. Williams, The Astrophysical Journal 995 (2025).","ama":"Setton DJ, Greene JE, de Graaff A, et al. Little Red Dots at an inflection point: Ubiquitous v-shaped turnover consistently occurs at the Balmer limit. <i>The Astrophysical Journal</i>. 2025;995(1). doi:<a href=\"https://doi.org/10.3847/1538-4357/ae1500\">10.3847/1538-4357/ae1500</a>","ista":"Setton DJ, Greene JE, de Graaff A, Ma Y逸伦, Leja J, Matthee JJ, Bezanson R, Boogaard LA, Cleri NJ, Katz H, Labbe I, Maseda MV, McConachie I, Miller TB, Price SH, Suess KA, van Dokkum P, Wang 王 B冰洁, Weibel A, Whitaker KE, Williams CC. 2025. Little Red Dots at an inflection point: Ubiquitous v-shaped turnover consistently occurs at the Balmer limit. The Astrophysical Journal. 995(1), 118.","mla":"Setton, David J., et al. “Little Red Dots at an Inflection Point: Ubiquitous v-Shaped Turnover Consistently Occurs at the Balmer Limit.” <i>The Astrophysical Journal</i>, vol. 995, no. 1, 118, IOP Publishing, 2025, doi:<a href=\"https://doi.org/10.3847/1538-4357/ae1500\">10.3847/1538-4357/ae1500</a>.","ieee":"D. J. Setton <i>et al.</i>, “Little Red Dots at an inflection point: Ubiquitous v-shaped turnover consistently occurs at the Balmer limit,” <i>The Astrophysical Journal</i>, vol. 995, no. 1. IOP Publishing, 2025.","apa":"Setton, D. J., Greene, J. E., de Graaff, A., Ma, Y. 逸伦, Leja, J., Matthee, J. J., … Williams, C. C. (2025). Little Red Dots at an inflection point: Ubiquitous v-shaped turnover consistently occurs at the Balmer limit. <i>The Astrophysical Journal</i>. IOP Publishing. <a href=\"https://doi.org/10.3847/1538-4357/ae1500\">https://doi.org/10.3847/1538-4357/ae1500</a>"},"type":"journal_article","issue":"1","intvolume":"       995","article_number":"118","doi":"10.3847/1538-4357/ae1500","article_processing_charge":"Yes","ddc":["520"],"user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","title":"Little Red Dots at an inflection point: Ubiquitous v-shaped turnover consistently occurs at the Balmer limit","file_date_updated":"2026-02-09T06:39:23Z","date_created":"2026-01-28T15:21:47Z","_id":"21057","publication":"The Astrophysical Journal","day":"09","article_type":"original","quality_controlled":"1","oa":1,"oa_version":"Published Version","publication_identifier":{"issn":["0004-637X"],"eissn":["1538-4357"]},"PlanS_conform":"1","scopus_import":"1","OA_place":"publisher","author":[{"last_name":"Setton","full_name":"Setton, David J.","first_name":"David J."},{"first_name":"Jenny E.","last_name":"Greene","full_name":"Greene, Jenny E."},{"first_name":"Anna","last_name":"de Graaff","full_name":"de Graaff, Anna"},{"full_name":"Ma, Yilun 逸伦","last_name":"Ma","first_name":"Yilun 逸伦"},{"first_name":"Joel","full_name":"Leja, Joel","last_name":"Leja"},{"first_name":"Jorryt J","id":"7439a258-f3c0-11ec-9501-9df22fe06720","last_name":"Matthee","full_name":"Matthee, Jorryt J","orcid":"0000-0003-2871-127X"},{"full_name":"Bezanson, Rachel","last_name":"Bezanson","first_name":"Rachel"},{"first_name":"Leindert A.","last_name":"Boogaard","full_name":"Boogaard, Leindert A."},{"last_name":"Cleri","full_name":"Cleri, Nikko J.","first_name":"Nikko J."},{"full_name":"Katz, Harley","last_name":"Katz","first_name":"Harley"},{"first_name":"Ivo","last_name":"Labbe","full_name":"Labbe, Ivo"},{"last_name":"Maseda","full_name":"Maseda, Michael V.","first_name":"Michael V."},{"first_name":"Ian","full_name":"McConachie, Ian","last_name":"McConachie"},{"full_name":"Miller, Tim B.","last_name":"Miller","first_name":"Tim B."},{"full_name":"Price, Sedona H.","last_name":"Price","first_name":"Sedona H."},{"first_name":"Katherine A.","full_name":"Suess, Katherine A.","last_name":"Suess"},{"full_name":"van Dokkum, Pieter","last_name":"van Dokkum","first_name":"Pieter"},{"first_name":"Bingjie 冰洁","full_name":"Wang 王, Bingjie 冰洁","last_name":"Wang 王"},{"last_name":"Weibel","full_name":"Weibel, Andrea","first_name":"Andrea"},{"first_name":"Katherine E.","full_name":"Whitaker, Katherine E.","last_name":"Whitaker"},{"first_name":"Christina C.","full_name":"Williams, Christina C.","last_name":"Williams"}],"DOAJ_listed":"1","publication_status":"published","year":"2025","volume":995,"has_accepted_license":"1","date_updated":"2026-02-09T06:41:48Z","publisher":"IOP Publishing","file":[{"creator":"dernst","file_size":1989640,"file_name":"2025_AstrophysicalJournal_Setton.pdf","date_created":"2026-02-09T06:39:23Z","access_level":"open_access","checksum":"2a424eb43748a6370ff058c98adb15c6","relation":"main_file","file_id":"21163","success":1,"date_updated":"2026-02-09T06:39:23Z","content_type":"application/pdf"}],"tmp":{"legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","short":"CC BY (4.0)","image":"/images/cc_by.png"},"external_id":{"arxiv":["2411.03424"]},"department":[{"_id":"JoMa"}],"abstract":[{"text":"Among the most puzzling early discoveries of JWST are “little red dots” (LRDs), compact red sources that host broad Balmer emission lines, and in many cases exhibit a “V-shaped” change in slope in the rest-optical. The physical properties of LRDs currently have order-of-magnitude uncertainties, because models to explain the continuum of these sources differ immensely. Here, we leverage the complete selection of red sources in the RUBIES program, supplemented with public PRISM spectra, to study the origin of this V shape. By fitting a broken power law with a flexible inflection point, we find that a large fraction of red Hα emitters at 2 < z < 6 exhibit a strong change in slope, and that all strong inflections appear associated with the Balmer limit (0.3645 μm). Using a simple model of a reddened active galactic nucleus (AGN) with an unobscured scattered-light component, we demonstrate that the observed V shape in LRDs is unlikely to occur at any specific wavelength if the entire continuum is dominated by light from a power-law AGN continuum. In contrast, models with an intrinsic feature at the Balmer limit, such as those that are dominated by an evolved stellar population, can produce the observed spectral shapes, provided that a reddened component picks up sufficiently redward of the break. While no model can comfortably explain the full LRD spectral energy distribution, the common inflection location suggests that a single component consistently dominates the rest-frame UV optical in LRDs, and that this component is associated with T ∼ 10^4 K hydrogen.","lang":"eng"}],"date_published":"2025-12-09T00:00:00Z","language":[{"iso":"eng"}],"arxiv":1,"acknowledgement":"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. The specific observations analyzed can be accessed via DOI: 10.17909/0esg-h949. All of the data products presented herein were retrieved from the Dawn JWST Archive (DJA). DJA is an initiative of the Cosmic Dawn Center, which is funded by the Danish National Research Foundation under grant No. 140. We express gratitude toward the members of the GTO, GO, and DDT teams, whose public data we utilized in this work.\r\n\r\nSupport for this work was provided by The Brinson Foundation through a Brinson Prize Fellowship grant. Support for program No. 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. This research was supported by the International Space Science Institute (ISSI) in Bern, through ISSI International Team project No. 562. D.S. acknowledges helpful conversations with Xiaohui Fan and Jared Siegel that contributed to the quality of this work, in addition to aesthetic sign-off from Stephanie Permut on the colors of figures. T.B.M. was supported by a CIERA fellowship. 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.","fulldoi":"https://doi.org/10.3847/1538-4357/ae1500"},{"_id":"21061","publication":"The Astrophysical Journal","file_date_updated":"2026-02-09T07:57:01Z","date_created":"2026-01-28T15:25:17Z","oa":1,"article_type":"original","day":"04","quality_controlled":"1","title":"GLIMPSE: An ultrafaint ≃10^5 M⊙ Pop III galaxy candidate and first constraints on the Pop III UV luminosity function at z ≃  6–7","user_id":"2DF688A6-F248-11E8-B48F-1D18A9856A87","article_number":"46","intvolume":"       989","doi":"10.3847/1538-4357/ade9a1","ddc":["520"],"article_processing_charge":"Yes","citation":{"ama":"Fujimoto S, Naidu RP, Chisholm J, et al. GLIMPSE: An ultrafaint ≃10^5 M⊙ Pop III galaxy candidate and first constraints on the Pop III UV luminosity function at z ≃  6–7. <i>The Astrophysical Journal</i>. 2025;989. doi:<a href=\"https://doi.org/10.3847/1538-4357/ade9a1\">10.3847/1538-4357/ade9a1</a>","ista":"Fujimoto S, Naidu RP, Chisholm J, Atek H, Endsley R, Kokorev V, Furtak LJ, Pan R, Liu B, Bromm V, Venditti A, Visbal E, Sarmento R, Weibel A, Oesch PA, Brammer G, Schaerer D, Adamo A, Berg DA, Bezanson R, Bouwens R, Chemerynska I, Claeyssens A, Dessauges-Zavadsky M, Frebel A, Korber D, Labbe I, Marques-Chaves R, Matthee JJ, McQuinn KBW, Muñoz JB, Natarajan P, Saldana-Lopez A, Suess KA, Volonteri M, Zitrin A. 2025. GLIMPSE: An ultrafaint ≃10^5 M⊙ Pop III galaxy candidate and first constraints on the Pop III UV luminosity function at z ≃  6–7. The Astrophysical Journal. 989, 46.","short":"S. Fujimoto, R.P. Naidu, J. Chisholm, H. Atek, R. Endsley, V. Kokorev, L.J. Furtak, R. Pan, B. Liu, V. Bromm, A. Venditti, E. Visbal, R. Sarmento, A. Weibel, P.A. Oesch, G. Brammer, D. Schaerer, A. Adamo, D.A. Berg, R. Bezanson, R. Bouwens, I. Chemerynska, A. Claeyssens, M. Dessauges-Zavadsky, A. Frebel, D. Korber, I. Labbe, R. Marques-Chaves, J.J. Matthee, K.B.W. McQuinn, J.B. Muñoz, P. Natarajan, A. Saldana-Lopez, K.A. Suess, M. Volonteri, A. Zitrin, The Astrophysical Journal 989 (2025).","chicago":"Fujimoto, Seiji, Rohan P. Naidu, John Chisholm, Hakim Atek, Ryan Endsley, Vasily Kokorev, Lukas J. Furtak, et al. “GLIMPSE: An Ultrafaint ≃10^5 M⊙ Pop III Galaxy Candidate and First Constraints on the Pop III UV Luminosity Function at z ≃  6–7.” <i>The Astrophysical Journal</i>. IOP Publishing, 2025. <a href=\"https://doi.org/10.3847/1538-4357/ade9a1\">https://doi.org/10.3847/1538-4357/ade9a1</a>.","apa":"Fujimoto, S., Naidu, R. P., Chisholm, J., Atek, H., Endsley, R., Kokorev, V., … Zitrin, A. (2025). GLIMPSE: An ultrafaint ≃10^5 M⊙ Pop III galaxy candidate and first constraints on the Pop III UV luminosity function at z ≃  6–7. <i>The Astrophysical Journal</i>. IOP Publishing. <a href=\"https://doi.org/10.3847/1538-4357/ade9a1\">https://doi.org/10.3847/1538-4357/ade9a1</a>","mla":"Fujimoto, Seiji, et al. “GLIMPSE: An Ultrafaint ≃10^5 M⊙ Pop III Galaxy Candidate and First Constraints on the Pop III UV Luminosity Function at z ≃  6–7.” <i>The Astrophysical Journal</i>, vol. 989, 46, IOP Publishing, 2025, doi:<a href=\"https://doi.org/10.3847/1538-4357/ade9a1\">10.3847/1538-4357/ade9a1</a>.","ieee":"S. Fujimoto <i>et al.</i>, “GLIMPSE: An ultrafaint ≃10^5 M⊙ Pop III galaxy candidate and first constraints on the Pop III UV luminosity function at z ≃  6–7,” <i>The Astrophysical Journal</i>, vol. 989. IOP Publishing, 2025."},"month":"08","OA_type":"gold","status":"public","type":"journal_article","date_published":"2025-08-04T00:00:00Z","abstract":[{"text":"Detecting the first generation of stars, Population III (Pop III), has been a long-standing goal in astrophysics, yet they remain elusive even in the JWST era. Here we present a novel NIRCam-based selection method for Pop III galaxies, and carefully validate it through completeness and contamination simulations. We systematically search ≃ 500 arcmin2 across JWST legacy fields for Pop III candidates, including GLIMPSE, which, assisted by gravitational lensing, has produced JWST’s deepest NIRCam imaging thus far. We discover one promising Pop III galaxy candidate (GLIMPSE-16043) at z=6.50 -0.24 +0.03, a moderately lensed galaxy (µ = + 2.9 -0.2 +0.1) with an intrinsic UV magnitude of MUV= -15.89 -0.14 +0.12. It exhibits key Pop III features: strong Hα emission (rest-frame EW 2810 ± 550 Å); a Balmer jump; no dust (UV slope β = −2.34 ± 0.36); and undetectable metal lines (e.g., [O III]; [O III]/Hβ < 0.44), implying a gas-phase metallicity of Zgas/Z⊙ < 0.5%. These properties indicate the presence of a nascent, metal-deficient young stellar population (<5 Myr) with a stellar mass of ≃105 M⊙. Intriguingly, this source deviates significantly from the extrapolated UV–metallicity relation derived from recent JWST observations at z = 4–10, consistent with UV enhancement by a top-heavy Pop III initial mass function or the presence of an extremely metal-poor active galactic nucleus. We also  derive the first observational constraints on the Pop III UV luminosity function at z ≃ 6–7. The volume density of GLIMPSE-16043 (≈10^−4 cMpc−3) is in excellent agreement with theoretical predictions, independently reinforcing its plausibility. This study demonstrates the power of our novel NIRCam method to finally reveal distant galaxies even more pristine than the Milky Way’s most metal-poor satellites, thereby promising to bring us closer to the first generation of stars than we have ever been before.","lang":"eng"}],"department":[{"_id":"JoMa"}],"fulldoi":"https://doi.org/10.3847/1538-4357/ade9a1","acknowledgement":"We are grateful to the CEERS, PRIMER, JOF, UNCOVER, and GLIMPSE teams for developing their NIRCam surveys, and to the various JWST and HST surveys acknowledged in Section 3 that enabled our search. We thank Kimihiko Nakajima and Kohei Inayoshi for sharing Pop III and/or AGN templates, Steven Finkelstein for comments on the completeness and contamination rate simulation, Aaron Yung for SEDs of simulated galaxies, Joel Leja, Ben Johnson, and Sandro Tacchella for advise on SED fitting, and Takashi Kojima and Hiroto Yanagisawa for discussions.\r\n\r\nWe made extensive use of the DAWN JWST Archive for various comparisons presented in this paper. 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. The prism spectra used in this paper were observed as part of the following programs, and we are grateful to these teams for helping build the rich spectroscopic legacy of JWST: 1180, 1181, 1210, 1286, 3215 (A. J. Bunker et al. 2024; F. D’Eugenio et al. 2024); 1211–1215 (M. V. Maseda et al. 2024); 1345 (S. L. Finkelstein et al. 2024); 1433 (T. Y.-Y. Hsiao et al. 2024); 1747 (G. Roberts-Borsani et al. 2025); 2028 (X. Wang et al. 2024); 2073 (PI: J. Hennawi); 2198 (L. Barrufet et al. 2025); 2282 (L. D. Bradley et al. 2023); 2561 (R. Bezanson et al. 2024; S. H. Price et al. 2024); 2565 (T. Nanayakkara et al. 2023); 2750 (P. Arrabal Haro et al. 2023b); 2756 (PI: W. Chen); 2767 (C. C. Williams et al. 2023); 3073 (M. Castellano et al. 2024); 4106 (PI: E. Nelson); 4233 (A. de Graaff et al. 2025); 4446 (B. L. Frye et al. 2024); 4557 (PI: H. Yan); 6541 (PI: E. Egami); 6585 (PI: D. Coulter).\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. The specific observations can be accessed via doi: 10.17909/xpxt-a441. These observations include data associated with program No. 03293. Support for program No. 03293 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.\r\n\r\nThis project has received funding from NASA through the NASA Hubble Fellowship grant HST-HF2-51505.001-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 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. H.A. and I.C. acknowledge 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. I.C. acknowledges funding support from the Initiative Physique des Infinis (IPI), a research training program of the Idex SUPER at Sorbonne Université. 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. P.N. acknowledges support from the Gordon and Betty Moore Foundation and the John Templeton Foundation that fund the black hole Initiative (BHI) at Harvard University, where she serves as one of the PIs. B.L. acknowledges support from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy EXC 2181/1—390900948 (the Heidelberg STRUCTURES Excellence Cluster). Y.S. and G.M. have received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement No. 833925, project STAREX).","language":[{"iso":"eng"}],"file":[{"file_size":14405059,"creator":"dernst","content_type":"application/pdf","success":1,"date_updated":"2026-02-09T07:57:01Z","file_id":"21167","access_level":"open_access","date_created":"2026-02-09T07:57:01Z","checksum":"9e08e77ce6d818fafd074e2b6c30bc43","relation":"main_file","file_name":"2025_AstrophysicalJournal_Fujimoto.pdf"}],"tmp":{"legal_code_url":"https://creativecommons.org/licenses/by/4.0/legalcode","name":"Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)","short":"CC BY (4.0)","image":"/images/cc_by.png"},"publication_status":"published","DOAJ_listed":"1","author":[{"full_name":"Fujimoto, Seiji","last_name":"Fujimoto","first_name":"Seiji"},{"last_name":"Naidu","full_name":"Naidu, Rohan P.","first_name":"Rohan P."},{"last_name":"Chisholm","full_name":"Chisholm, John","first_name":"John"},{"first_name":"Hakim","full_name":"Atek, Hakim","last_name":"Atek"},{"first_name":"Ryan","last_name":"Endsley","full_name":"Endsley, Ryan"},{"full_name":"Kokorev, Vasily","last_name":"Kokorev","first_name":"Vasily"},{"last_name":"Furtak","full_name":"Furtak, Lukas J.","first_name":"Lukas J."},{"full_name":"Pan, Richard","last_name":"Pan","first_name":"Richard"},{"first_name":"Boyuan","last_name":"Liu","full_name":"Liu, Boyuan"},{"last_name":"Bromm","full_name":"Bromm, Volker","first_name":"Volker"},{"first_name":"Alessandra","last_name":"Venditti","full_name":"Venditti, Alessandra"},{"full_name":"Visbal, Eli","last_name":"Visbal","first_name":"Eli"},{"full_name":"Sarmento, Richard","last_name":"Sarmento","first_name":"Richard"},{"first_name":"Andrea","last_name":"Weibel","full_name":"Weibel, Andrea"},{"last_name":"Oesch","full_name":"Oesch, Pascal A.","first_name":"Pascal A."},{"last_name":"Brammer","full_name":"Brammer, Gabriel","first_name":"Gabriel"},{"first_name":"Daniel","full_name":"Schaerer, Daniel","last_name":"Schaerer"},{"first_name":"Angela","full_name":"Adamo, Angela","last_name":"Adamo"},{"first_name":"Danielle A.","last_name":"Berg","full_name":"Berg, Danielle A."},{"last_name":"Bezanson","full_name":"Bezanson, Rachel","first_name":"Rachel"},{"first_name":"Rychard","full_name":"Bouwens, Rychard","last_name":"Bouwens"},{"first_name":"Iryna","full_name":"Chemerynska, Iryna","last_name":"Chemerynska"},{"full_name":"Claeyssens, Adélaïde","last_name":"Claeyssens","first_name":"Adélaïde"},{"full_name":"Dessauges-Zavadsky, Miroslava","last_name":"Dessauges-Zavadsky","first_name":"Miroslava"},{"last_name":"Frebel","full_name":"Frebel, Anna","first_name":"Anna"},{"last_name":"Korber","full_name":"Korber, Damien","first_name":"Damien"},{"first_name":"Ivo","last_name":"Labbe","full_name":"Labbe, Ivo"},{"full_name":"Marques-Chaves, Rui","last_name":"Marques-Chaves","first_name":"Rui"},{"orcid":"0000-0003-2871-127X","last_name":"Matthee","full_name":"Matthee, Jorryt J","id":"7439a258-f3c0-11ec-9501-9df22fe06720","first_name":"Jorryt J"},{"last_name":"McQuinn","full_name":"McQuinn, Kristen B. W.","first_name":"Kristen B. W."},{"last_name":"Muñoz","full_name":"Muñoz, Julian B.","first_name":"Julian B."},{"first_name":"Priyamvada","full_name":"Natarajan, Priyamvada","last_name":"Natarajan"},{"first_name":"Alberto","last_name":"Saldana-Lopez","full_name":"Saldana-Lopez, Alberto"},{"first_name":"Katherine A.","full_name":"Suess, Katherine A.","last_name":"Suess"},{"first_name":"Marta","last_name":"Volonteri","full_name":"Volonteri, Marta"},{"first_name":"Adi","last_name":"Zitrin","full_name":"Zitrin, Adi"}],"OA_place":"publisher","scopus_import":"1","publisher":"IOP Publishing","has_accepted_license":"1","date_updated":"2026-02-09T08:11:01Z","volume":989,"year":"2025","oa_version":"Published Version","PlanS_conform":"1","publication_identifier":{"eissn":["1538-4357"],"issn":["0004-637X"]}}]