@article{21998, abstract = {Little Red Dots (LRDs), among the most enigmatic high-redshift discoveries by JWST, are commonly believed to be powered by accreting supermassive black holes. Here, we explore the possibility that these sources are globular clusters in formation, with rest-frame UV arising from a very young stellar population and rest-frame optical from a short-lived supermassive (>104 M⊙) star. The spectral profiles of LRDs are broadly consistent with this scenario, though the observed temperatures and bolometric luminosities favor emission reprocessed by optically thick continuum-driven winds not fully captured by current models. The LRD z ∼ 5−7 UV luminosity function naturally evolves, under standard evolutionary and mass-loss prescriptions, into a present-day mass function with a turnover at log10(M*/M⊙) = 5.3 and an exponential cutoff at high masses, consistent with local globular cluster populations. We estimate the total present-day number density of LRDs formed across all redshifts to be ≈0.3 Mpc−3, similar within uncertainties to local globular clusters. The observed LRD redshift range matches the age distribution of metal-poor globular clusters, without current LRD counterparts to the metal-rich population. If LRDs are globular clusters in formation, we predict chemical abundance patterns characteristic of multiple stellar populations, including enhanced He and N, and potential Na–O and Al–Mg anticorrelations. These results offer a local perspective to explore this surprisingly abundant population of distant sources, and a potential new window into extreme stellar astrophysics in the early Universe.}, author = {Chisholm, John and Berg, Danielle A. and Boylan-Kolchin, Michael and De Graaff, Anna and Furtak, Lukas J. and Kokorev, Vasily and Matthee, Jorryt J and Muñoz, Julian B. and Naidu, Rohan P. and Sander, Andreas A.C.}, issn = {2041-8213}, journal = {The Astrophysical Journal Letters}, number = {1}, publisher = {IOP Publishing}, title = {{Little Red Dots as globular clusters in formation}}, doi = {10.3847/2041-8213/ae6dae}, volume = {1004}, year = {2026}, } @article{21999, abstract = {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.}, author = {Fei, Qinyue and Fujimoto, Seiji and Naidu, Rohan P. and Chisholm, John and Atek, Hakim and Brammer, Gabriel and Asada, Yoshihisa and Berg, Danielle A. and Bromm, Volker and Furtak, Lukas J. and Greene, Jenny E. and Hsiao, Tiger Yu Yang and Jeon, Junehyoung and Kokorev, Vasily and Matthee, Jorryt J and Natarajan, Priyamvada and Pan, Richard and Richard, Johan and Saldana-Lopez, Alberto and Schaerer, Daniel and Volonteri, Marta and Zitrin, Adi}, issn = {1538-4357}, journal = {The Astrophysical Journal}, number = {2}, publisher = {IOP Publishing}, title = {{A GLIMPSE of intermediate mass Black Holes in the epoch of reionization: Witnessing the descendants of direct collapse?}}, doi = {10.3847/1538-4357/ae6248}, volume = {1003}, year = {2026}, } @article{21038, abstract = {Little Red Dots (LRDs) are compact sources at z > 5 discovered through James Webb Space Telescope spectroscopy. Their spectra exhibit broad Balmer emission lines (>~1000 km s^−1), alongside absorption features and a pronounced Balmer break – evidence for a dense, neutral hydrogen medium, in which the n = 2 state is significantly populated. When interpreted as arising from active galactic nucleus broad-line regions, inferred black hole masses from local scaling relations exceed expectations given their stellar masses, challenging models of early black hole–galaxy co-evolution. However, radiative transfer effects in dense media may also impact the formation of hydrogen emission lines. We model three scattering processes shaping hydrogen line profiles: resonance scattering by hydrogen in the n = 2 state, Raman scattering of ultraviolet (UV) radiation by ground-state hydrogen, and Thomson scattering by free electrons. Using 3D Monte Carlo radiative transfer simulations, we examine their imprint on line shapes and ratios. Resonance scattering produces strong deviations from Case B flux ratios, clear differences between Hα and Hβ, and encodes gas kinematics in line profiles but cannot broaden Hβ due to conversion to Paα. While Raman scattering can yield broad wings, scattering of the UV continuum is disfavoured given the absence of strong full width at half-maximum variations across transitions. Raman scattering of higher Lyman-series emission can produce Hα/Hβ wing width ratios of >~1.28, agreeing with observations. Thomson scattering can reproduce the observed >~ 1000 km s^−1 wings under plausible conditions – e.g. Te ∼ 10^4 K and Ne ∼ 10^24 cm^−2 – and lead to black hole mass overestimates by factors 10. Our results provide a framework for interpreting hydrogen lines in LRDs and similar systems.}, author = {Chang, Seok Jun and Gronke, Max and Matthee, Jorryt J and Mason, Charlotte}, issn = {1365-2966}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {4}, publisher = {Oxford University Press}, title = {{Impact of resonance, Raman, and Thomson scattering on hydrogen line formation in Little Red Dots}}, doi = {10.1093/mnras/staf2131}, volume = {545}, year = {2026}, } @article{21341, abstract = {We aim to characterise the mass-metallicity relation (MZR) and the 3D correlation between the stellar mass, metallicity, and star formation rate (SFR) known as the fundamental metallicity relation (FMR) for galaxies at 5 < z < 7. Using ∼800 [O III] selected galaxies from deep NIRCam grism surveys, we present our stacked measurements of direct-Te metallicities, which we used to test recent strong-line metallicity calibrations. Our measured direct-Te metallicities (0.1–0.2 Z⊙ for M★ ≈ 5 × 107 − 9 M⊙, respectively) match recent JWST/NIRSpec-based results. However, there are significant inconsistencies between observations and hydrodynamical simulations. We observe a flatter MZR slope than the SPHINX20 and FLARES simulations, which cannot be attributed to selection effects. With simple models, we show that the effect of an [O III] flux-limited sample on the observed shape of the MZR is strongly dependent on the FMR. If the FMR is similar to the one in the local Universe, the intrinsic high-redshift MZR should be even flatter than is observed. In turn, a 3D relation where SFR correlates positively with metallicity at fixed mass would imply an intrinsically steeper MZR. Our measurements indicate that metallicity variations at fixed mass show little dependence on the SFR, suggesting a flat intrinsic MZR. This could indicate that the low-mass galaxies at these redshifts are out of equilibrium and that metal enrichment occurs rapidly in low-mass galaxies. However, being limited by our stacking analysis, we are yet to probe the scatter in the MZR and its dependence on SFR. Large carefully selected samples of galaxies with robust metallicity measurements can put tight constraints on the high-redshift FMR and help us to understand the interplay between gas flows, star formation, and feedback in early galaxies.}, author = {Kotiwale, Gauri and Matthee, Jorryt J and Kashino, Daichi and Vijayan, Aswin P. and Torralba Torregrosa, Alberto and Di Cesare, Claudia and Iani, Edoardo and Bordoloi, Rongmon and Leja, Joel and Maseda, Michael V. and Tacchella, Sandro and Shivaei, Irene and Heintz, Kasper E. and Danhaive, A. Lola and Mascia, Sara and Kramarenko, Ivan and Navarrete, Benjamín and Mackenzie, Ruari and Naidu, Rohan P. and Sobral, David}, issn = {1432-0746}, journal = {Astronomy & Astrophysics}, publisher = {EDP Sciences}, title = {{Rapid, out-of-equilibrium metal enrichment indicated by a flat mass-metallicity relation at z ∼ 6 from NIRCam grism spectroscopy}}, doi = {10.1051/0004-6361/202556597}, volume = {706}, year = {2026}, } @article{21342, abstract = {JWST has revealed a stunning population of bright galaxies at surprisingly early epochs, z > 10, where few such sources were expected. Here we present the most distant example of this class yet – MoM-z14, a luminous (MUV = −20.2) source in the COSMOS legacy field at zspec = 14.44+0.02−0.02 that expands the observational frontier to a mere 280 million years after the Big Bang. The redshift is confirmed with NIRSpec/prism spectroscopy through a sharp Lyman-α break and ≈ 3σ detections of five rest-UV emission lines. The number density of bright zspec ≈ 14 − 15 sources implied by our “Mirage or Miracle” survey spanning ≈ 350 arcmin2 is > 100× larger (182+329 −105×) than pre-JWST consensus models. The high EWs of UV lines (≈15−35˚A) signal a rising star-formation history, with a ≈10× increase in the last 5 Myr (SFR5Myr/SFR50Myr = 9.9 +3.0 −5.8). The source is extremely compact (circularized re = 74+15 −12 pc), and yet elongated (b/a = 0.25+0.11−0.06), suggesting an AGN is not the dominant source of UV light. The steep UV slope (β = −2.5 +0.2 −0.2) implies negligible dust attenuation and a young stellar population. The absence of a strong damping wing provides tentative evidence that the immediate surroundings of MoM-z14 may be partially ionized at a redshift where virtually every reionization model predicts a ≈ 100% neutral fraction. The nitrogen emission and highly supersolar [N/C]> 1 hint at an abundance pattern similar to local globular clusters that may have once hosted luminous supermassive stars. Since this abundance pattern is also common among the most ancient stars born in the Milky Way, we may be directly witnessing the formation of such stars in dense clusters, connecting galaxy evolution across the entire sweep of cosmic time. }, author = {Naidu, Rohan P. and Oesch, Pascal A. and Brammer, Gabriel and Weibel, Andrea and Li, Yijia and Matthee, Jorryt J and Chisholm, John and Pollock, Clara L. and Heintz, Kasper E. and Johnson, Benjamin D. and Shen, Xuejian and Hviding, Raphael E. and Leja, Joel and Tacchella, Sandro and Ganguly, Arpita and Witten, Callum and Atek, Hakim and Belli, Sirio and Bose, Sownak and Bouwens, Rychard and Dayal, Pratika and Decarli, Roberto and De Graaff, Anna and Fudamoto, Yoshinobu and Giovinazzo, Emma and Greene, Jenny E. and Illingworth, Garth and Inoue, Akio K. and Kane, Sarah G. and Labbe, Ivo and Leonova, Ecaterina and Marques-Chaves, Rui and Meyer, Romain A. and Nelson, Erica J. and Roberts-Borsani, Guido and Schaerer, Daniel and Simcoe, Robert A. and Stefanon, Mauro and Sugahara, Yuma and Toft, Sune and Van Der Wel, Arjen and Van Dokkum, Pieter and Walter, Fabian and Watson, Darach and Weaver, John R. and Whitaker, Katherine E.}, issn = {2565-6120}, journal = {The Open Journal of Astrophysics}, publisher = {Maynooth Academic Publishing}, title = {{A cosmic miracle: A remarkably luminous galaxy at zspec = 14.44 confirmed with JWST}}, doi = {10.33232/001c.156033}, volume = {9}, year = {2026}, } @article{21371, abstract = {There may be a newly identified early phase of supermassive black hole growth}, author = {Matthee, Jorryt J}, issn = {1095-9203}, journal = {Science}, number = {6787}, pages = {767--768}, publisher = {AAAS}, title = {{Black holes disguised as little red dots}}, doi = {10.1126/science.adz8603}, volume = {391}, year = {2026}, } @article{21380, abstract = {Context. Extreme emission line galaxies (EELGs) are believed to significantly contribute to the star formation activity and mass assembly in galaxies. EELGs likely also play a leading role in the cosmic re-ionization as their interstellar medium may allow a significant fraction of their ionizing photons to escape (> 5%). Finding low-redshift analogues of these high-z galaxies is therefore essential to characterizing the physical conditions in the interstellar medium of these galaxies and understanding the processes that re-ionized the Universe. Aims. We aimed to develop a robust and efficient method for the photometric identification of EELGs using the J-PAS survey. J-PAS will cover approximately 8500 deg2 of the sky with 54 narrow-band filters in the optical range plus i-SDSS, enabling detailed studies of the physical properties of these galaxies. In this work we focused on an initial subset of the survey: a 30 square degree area with complete observations in all bands. Methods. We combine equivalent width (EW) measurements from J-PAS narrow-band photometry with artificial intelligence techniques to identify galaxies with emission lines exceeding 300 Å. We validated our selection using spectroscopic data from DESI DR1 and characterized the selected sample through spectral energy distribution fitting with CIGALE. Results. We identify 917 EELGs up to z = 0.8 over 30 deg2, achieving a purity of 95% and a completeness of 96% for i-SDSS < 22.5 mag. Importantly, active galactic nucleus contamination was carefully considered and is estimated to be around 5%. Furthermore, a cross-match with DESI yielded 79 counterparts; their redshifts are in excellent agreement with our photometric estimates, thereby confirming the reliability of our redshift determination. In addition, the derived emission line fluxes are in good agreement with spectroscopic measurements. Moreover, the selected sample reveals strong correlations between the ionizing photon production efficiency (ξion) and EW(Hβ), which are consistent with previous observational studies at low and high redshifts and theoretical expectations. Finally, most of the sources surpass the ionizing efficiency threshold required for re-ionization, highlighting their relevance as local analogues of early-Universe galaxies.}, author = {Giménez-Alcázar, A. and Amorín, R. and Vílchez, J. M. and Hernán-Caballero, A. and González-Otero, M. and Arroyo-Polonio, A. and Iglesias-Páramo, J. and Lumbreras-Calle, A. and Fernández-Ontiveros, J. A. and López-Sanjuan, C. and Bonatto, L. and González Delgado, R. M. and Kehrig, C. and Torralba Torregrosa, Alberto and Rahna, P. T. and Jiménez-Teja, Y. and Márquez, I. and Breda, I. and Álvarez-Candal, A. and Abramo, R. and Alcaniz, J. and Benitez, N. and Bonoli, S. and Carneiro, S. and Cenarro, J. and Cristóbal-Hornillos, D. and Dupke, R. and Ederoclite, A. and Hernández-Monteagudo, C. and Marín-Franch, A. and Mendes de Oliveira, C. and Moles, M. and Sodré, L. and Taylor, K. and Varela, J. and Vázquez Ramió, H.}, issn = {1432-0746}, journal = {Astronomy & Astrophysics}, publisher = {EDP Sciences}, title = {{J-PAS: First identification, physical properties, and ionization efficiency of extreme emission line galaxies}}, doi = {10.1051/0004-6361/202557358}, volume = {706}, year = {2026}, } @article{21451, abstract = {The population of the little red dots (LRDs) may represent a key phase of supermassive black hole (SMBH) growth. A cocoon of dense excited gas is emerging as a key component to explain the most striking properties of LRDs, such as strong Balmer breaks and Balmer absorption, as well as the weak IR emission. To dissect the structure of LRDs, we analyzed new deep JWST/NIRSpec PRISM and G395H spectra of FRESCO-GN-9771, one of the most luminous known LRDs at z = 5.5. These spectra reveal a strong Balmer break, broad Balmer lines, and very narrow [O III] emission. We revealed a forest of optical [Fe II] lines, which we argue are emerging from a dense (nH = 109 − 10 cm−3) warm layer with electron temperature Te ≈ 7000 K. The broad wings of Hα and Hβ have an exponential profile due to electron scattering in this same layer. The high Hα : Hβ : Hγ flux ratio of ≈10.4 : 1 : 0.14 is an indicator of collisional excitation and resonant scattering dominating the Balmer line emission. A narrow Hγ component, unseen in the other two Balmer lines due to outshining by the broad components, could trace the ISM of a normal host galaxy with a star formation rate of ∼5 M⊙ yr−1. The warm layer is mostly opaque to Balmer transitions, producing a characteristic P Cygni profile in the line centers suggesting outflowing motions. This same layer is responsible for shaping the Balmer break. The broadband spectrum can be reasonably matched by a simple photoionized slab model that dominates the λ > 1500 Å continuum and a low-mass (∼108 M⊙) galaxy that could explain the narrow [O III], with only a subdominant contribution to the UV continuum. Our findings indicate that Balmer lines are not directly tracing the gas kinematics near the SMBH and that the BH mass scale is likely much lower than virial indicators suggest.}, author = {Torralba Torregrosa, Alberto and Matthee, Jorryt J and Pezzulli, Gabriele and Naidu, Rohan P. and Ishikawa, Yuzo and Brammer, Gabriel B. and Chang, Seok Jun and Chisholm, John and De Graaff, Anna and D’Eugenio, Francesco and Di Cesare, Claudia and Eilers, Anna Christina and Greene, Jenny E. and Gronke, Max and Iani, Edoardo and Kokorev, Vasily and Kotiwale, Gauri and Kramarenko, Ivan and Ma, Yilun and Mascia, Sara and Navarrete, Benjamín and Nelson, Erica and Oesch, Pascal and Simcoe, Robert A. and Wuyts, Stijn}, issn = {1432-0746}, journal = {Astronomy & Astrophysics}, publisher = {EDP Sciences}, title = {{The warm outer layer of a little red dot as the source of [Fe ii] and collisional Balmer lines with scattering wings}}, doi = {10.1051/0004-6361/202557537}, volume = {707}, year = {2026}, } @article{21452, abstract = {Galaxies exhibit a tight correlation between their star formation rate (SFR) and stellar mass over a wide redshift range known as the star-forming main sequence (SFMS). With JWST, the SFMS can now be investigated at high redshifts down to masses of ∼106 M⊙, using sensitive star formation rate tracers such as the Hα emission, which allow us to probe the variability in the star formation histories. We present inferences of the SFMS based on 316 Hα-selected galaxies at z ∼ 4 − 5 with log(M★/M⊙) = 6.4 − 10.6. These galaxies were identified behind the Abell 2744 lensing cluster with NIRCam grism spectroscopy from the survey All the Little Things (ALT). At face value, our data suggest a shallow slope in the SFMS (SFR ∝ M★α, with α = 0.45). After we corrected this for the Hα-flux limited nature of our survey using a Bayesian framework, the slope steepened to α = 0.59+0.10−0.09, whereas current data on their own are inconclusive on the mass dependence of the scatter. These slopes differ significantly from the slope of ∼1 that is expected from the observed evolution of the galaxy stellar mass function and from simulations. When we fixed the slope to α = 1, we found evidence for a decreasing intrinsic scatter with stellar mass (from ∼0.5 dex at M★ = 108 M⊙ to 0.4 dex at M★ = 1010 M⊙). This difference might be explained by a (combination of) luminosity-dependent SFR(Hα) calibration, a population of (mini)-quenched low-mass galaxies, or underestimated dust attenuation in high-mass galaxies. Future deep observations with different facilities can quantify these processes, which will enable us to achieve better insights into the variability of the star formation histories.}, author = {Di Cesare, Claudia and Matthee, Jorryt J and Naidu, Rohan P. and Torralba, Alberto and Kotiwale, Gauri and Kramarenko, Ivan and Blaizot, Jeremy and Rosdahl, Joakim and Leja, Joel and Iani, Edoardo and Adamo, Angela and Covelo-Paz, Alba and Furtak, Lukas J. and Heintz, Kasper E. and Mascia, Sara and Navarrete, Benjamín and Oesch, Pascal A. and Romano, Michael and Shivaei, Irene and Tacchella, Sandro}, issn = {1432-0746}, journal = {Astronomy & Astrophysics}, publisher = {EDP Sciences}, title = {{The slope and scatter of the star-forming main sequence at z ∼ 5: Reconciling observations with simulations}}, doi = {10.1051/0004-6361/202557790}, volume = {707}, year = {2026}, } @article{21481, abstract = {The Hα emission line in galaxies is a powerful tracer of their recent star formation activity. With the advent of JWST, we are now able to routinely observe Hα in galaxies at high redshift (z ≳ 3) and thus measure their star formation rates (SFRs). However, using classical SFR(Hα) calibrations to derive the SFRs leads to biased results because high-redshift galaxies are commonly characterized by low metallicities and bursty star formation histories, affecting the conversion factor between the Hα luminosity (LHα) and the SFR. We developed a set of new SFR(Hα) calibrations that allowed us to predict the SFRs of Hα-emitters at z ≳ 3 with very little error. We used the SPHINX cosmological simulations to select a sample of star-forming galaxies representative of the Hα-emitter population observed with JWST. We then derived linear corrections to the classical SFR(Hα) calibrations that took variations in the physical properties (e.g., stellar metallicities) among individual galaxies into account. We obtained two new SFR(Hα) calibrations that compared to the classical calibrations reduce the root mean squared error (RMSE) in the predicted SFRs by ΔRMSE ≈ 0.04 dex and ΔRMSE ≈ 0.06 dex, respectively. Using the recent JWST NIRCam/grism observations of Hα-emitters at z ∼ 6, we show that the new calibrations affect the high-redshift galaxy population statistics: (i) the estimated cosmic SFR density decreases by ΔρSFR ≈ 12%, and (ii) the observed slope of the star formation main sequence increases by Δ∂logSFR/∂logM★ = 0.08 ± 0.02.}, author = {Kramarenko, Ivan and Rosdahl, J. and Blaizot, J. and Matthee, Jorryt J and Katz, H. and Di Cesare, Claudia}, issn = {1432-0746}, journal = {Astronomy & Astrophysics}, publisher = {EDP Sciences}, title = {{H α as a tracer of star formation in the SPHINX cosmological simulations}}, doi = {10.1051/0004-6361/202557114}, volume = {707}, year = {2026}, } @article{21709, abstract = {JWST’s “little red dots” (LRDs) are increasingly interpreted as active galactic nuclei (AGN) obscured by dense thermalized gas rather than dust as evidenced by their X-ray weakness, blackbody-like continua, and Balmer line profiles. Key questions are how LRDs connect to standard UV-luminous AGN, whether transitional phases exist, and whether they are observable. We present the “X-ray dot” (XRD), a compact source at z = 3.28 observed by the NIRSpec Wide Guaranteed Time Observation survey. The XRD exhibits LRD hallmarks: a blackbody-like (Teff ≃ 6400 K) red continuum, a faint but blue rest-UV excess, falling mid-IR emission, and broad Balmer lines (FWHM ∼ 2700–3200 km s−1). Unlike LRDs, however, it is remarkably X-ray luminous (L2−10 keV = 1044.18 erg s−1) and has a continuum inflection that is blueward of the Balmer limit. We find that the red rest-optical and blue mid-IR continuum cannot be reproduced by standard dust-attenuated AGN models without invoking extremely steep extinction curves, nor can the weak mid-IR emission be reconciled with well-established X-ray–torus scaling relations. We therefore consider an alternative scenario: the XRD may be an LRD in transition, where the gas envelope dominates the optical continuum but optically thin sight lines allow X-rays to escape. The XRD may thus provide a physical link between LRDs and standard AGN, offering direct evidence that LRDs are powered by supermassive black holes and providing insight into their accretion properties.}, author = {Hviding, Raphael E. and De Graaff, Anna and Liu, Hanpu and Goulding, Andy D. and Ma, Yilun and Greene, Jenny E. and Boogaard, Leindert A. and Bunker, Andrew J. and Cleri, Nikko J. and Franx, Marijn and Hirschmann, Michaela and Leja, Joel and Matthee, Jorryt J and Naidu, Rohan P. and Setton, David J. and Übler, Hannah and Venturi, Giacomo and Wang, Bingjie}, issn = {2041-8213}, journal = {The Astrophysical Journal Letters}, number = {1}, publisher = {IOP Publishing}, title = {{The X-ray dot: Exotic dust or a late-stage Little Red Dot?}}, doi = {10.3847/2041-8213/ae4c88}, volume = {1000}, year = {2026}, } @article{21710, abstract = {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 object (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.}, author = {Papovich, Casey and Cole, Justin W. and Hu, Weida and Finkelstein, Steven L. and Shen, Lu and Arrabal Haro, Pablo and Amorín, Ricardo O. and Backhaus, Bren E. and Bagley, Micaela B. and Bhatawdekar, Rachana and Calabrò, Antonello and Carnall, Adam C. and Cleri, Nikko J. and Daddi, Emanuele and Dickinson, Mark and Grogin, Norman A. and Holwerda, Benne W. and Jaskot, Anne E. and Koekemoer, Anton M. and Llerena, Mario and Lucas, Ray A. and Mascia, Sara and Pacucci, Fabio and Pentericci, Laura and Pérez-González, Pablo G. and Pirzkal, Nor and Raghunathan, Srinivasan and Seillé, Lise Marie and Somerville, Rachel S. and Yung, L. Y.Aaron}, issn = {1538-4357}, journal = {The Astrophysical Journal}, number = {1}, publisher = {IOP Publishing}, title = {{Galaxies in the epoch of reionization are all bark and no bite-plenty of ionizing photons, low escape fractions}}, doi = {10.3847/1538-4357/ae3b25}, volume = {1000}, year = {2026}, } @article{21715, abstract = {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.}, author = {Greene, Jenny E. and Setton, David J. and Furtak, Lukas J. and Naidu, Rohan P. and Volonteri, Marta and Dayal, Pratika and Labbe, Ivo and Van Dokkum, Pieter and Bezanson, Rachel and Brammer, Gabriel and Cutler, Sam E. and Glazebrook, Karl and De Graaff, Anna and Hirschmann, Michaela and Hviding, Raphael E. and Kokorev, Vasily and Leja, Joel and Liu, Hanpu and Ma, Yilun and Matthee, Jorryt J and Nanayakkara, Themiya and Oesch, Pascal A. and Pan, Richard and Price, Sedona H. and Spilker, Justin S. and Wang, Bingjie and Weaver, John R. and Whitaker, Katherine E. and Williams, Christina C. and Zitrin, Adi}, issn = {1538-4357}, journal = {The Astrophysical Journal}, number = {2}, publisher = {IOP Publishing}, title = {{What you see is what you get: Empirically measured bolometric luminosities of Little Red Dots}}, doi = {10.3847/1538-4357/ae1836}, volume = {996}, year = {2026}, } @article{21846, abstract = {We compile a sample of 83 little red dots (LRDs) with JWST imaging and find that a substantial fraction (∼43%, rising to ≳80% for the most luminous LRDs) host one or more spatially offset, UV-bright companions at projected separations of 0.5 kpc ≲ d ≲ 5 kpc, with median 〈d〉 = 1.0 kpc. This fraction is even higher when smaller spatial scales are probed at high signal-to-noise ratio: the two most strongly lensed LRDs, A383-LRD1 and the newly discovered A68-LRD1, both have UV-bright companions at separations of only d ∼ 0.3 kpc, below the resolution limit of most unlensed JWST samples. We explore whether these ubiquitous red/blue configurations may be physically linked to the formation of LRDs, in analogy with the “synchronized pair” scenario originally proposed for direct-collapse black hole formation. In this picture, UV radiation from the companions, with typically modest stellar masses (M∗ ∼ 108−109 M⊙), suppresses molecular hydrogen cooling in nearby gas, allowing nearly isothermal collapse and the formation of extremely compact objects, such as massive black holes, supermassive stars, or quasi-stars. Using component-resolved photometry and spectral energy distribution modeling, we infer Lyman–Werner radiation fields of J21,LW ∼ 102.5–105 at the locations of the red components, comparable to those required in direct-collapse models, suggesting that the necessary photodissociation conditions are realized in many LRD systems. This framework provides a simple and self-consistent explanation for the extreme compactness and distinctive spectral properties of LRDs and links long-standing theoretical models for early compact object formation directly to a population now observed with JWST in the early Universe.}, author = {Baggen, Josephine F.W. and Scoggins, Matthew T. and Van Dokkum, Pieter and Haiman, Zoltán and Torralba Torregrosa, Alberto and Matthee, Jorryt J}, issn = {2041-8213}, journal = {The Astrophysical Journal Letters}, number = {1}, publisher = {IOP Publishing}, title = {{Connecting the dots: UV-bright companions of Little Red Dots as Lyman–Werner sources enabling direct-collapse Black Hole formation}}, doi = {10.3847/2041-8213/ae58a5}, volume = {1002}, year = {2026}, } @article{21882, abstract = {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.}, author = {Wang, Bingjie and Leja, Joel and Katz, Harley and Inayoshi, Kohei and Cleri, Nikko J. and De Graaff, Anna and Hviding, Raphael E. and Van Dokkum, Pieter and Greene, Jenny E. and Labbé, Ivo and Matthee, Jorryt J and Mcconachie, Ian and Naidu, Rohan P. and Nelson, Erica J.}, issn = {1538-4357}, journal = {The Astrophysical Journal}, number = {1}, publisher = {IOP Publishing}, title = {{The missing hard photons of Little Red Dots: Their incident ionizing spectra resemble massive stars}}, doi = {10.3847/1538-4357/ae5bab}, volume = {1003}, year = {2026}, } @article{21898, abstract = {We investigate the nature and spectroscopic diversity of early galaxies from a sample of 41 sources at $z\geqslant 10$ with James Webb Space Telescope (JWST)/NIRSpec prism observations. We compare the properties of strong ultraviolet (UV) line emitters, traced by intense C iv emission, with those of more ‘typical’ sources with weak or undetected C iv. The more typical (or ‘C iv-weak’) sources reveal significant scatter in their C iii] line strengths, UV continuum slopes, and physical sizes, spanning C iii] equivalent widths (EWs) of $\sim$1–51 Å, UV slopes of $\beta \sim -1.6$ to $-2.6$, and half-light radii of $\sim$50–1000 pc. In contrast, C iv-strong sources occupy the tail of these distributions, with C iii] EWs of 16–51 Å, UV slopes $\beta \lesssim -2.5$, compact morphologies ($r_{\rm 50} \lesssim 100$ pc), and elevated star formation surface densities ($\Sigma _{\rm SFR} \gtrsim 100\, M_\odot \, \mathrm{yr}^{-1}\, \mathrm{kpc}^{-2}$). These properties suggest concentrated starbursts that temporarily outshine the host galaxy. Comparing average properties from composite spectra, we find the diversity of the sample is primarily driven by bursty star formation on very short time-scales ($\le$3 Myr), with strong C iv emitters observed at the apex of the bursts and sources devoid of emission lines during relative inactivity. An apparent association between strong C iv and enhanced nitrogen abundance suggests both may be modulated by the same duty cycle, reflecting a generic mode of star formation. We show that active galactic nuclei are unlikely to contribute significantly to this duty cycle based on UV line diagnostics and photoionization models. Our results support a picture whereby brief bursts and lulls can explain the spectral diversity and early growth of bright galaxies in the first 500 Myr.}, author = {Roberts-Borsani, Guido and Oesch, Pascal A and Ellis, Richard and Weibel, Andrea and Giovinazzo, Emma and Bouwens, Rychard and Dayal, Pratika and Fontana, Adriano and Heintz, Kasper E and Matthee, Jorryt J and Meyer, Romain A and Pentericci, Laura and Shapley, Alice and Tacchella, Sandro and Treu, Tommaso and Walter, Fabian and Atek, Hakim and Bose, Sownak and Castellano, Marco and Fudamoto, Yoshinobu and Morishita, Takahiro and Naidu, Rohan P and Sanders, Ryan L and van der Wel, Arjen}, issn = {1365-2966}, journal = {Monthly Notices of the Royal Astronomical Society}, number = {3}, publisher = {Oxford University Press}, title = {{JWST spectroscopic insights into the diversity of galaxies in the first 500 Myr: Short-lived snapshots along a common evolutionary pathway}}, doi = {10.1093/mnras/stag701}, volume = {548}, year = {2026}, } @article{21930, abstract = {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 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 ( 12 + log(O/H) = 7.753 ± 0.025 ), and a nonuniform elemental enrichment pattern of extreme N/O enhancement ( log(N/O) = 0.391 ± 0.037 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.}, author = {Berg, Danielle A. and Naidu, Rohan P. and Chisholm, John and Atek, Hakim and Fujimoto, Seiji and Kokorev, Vasily and Furtak, Lukas J. and Kobayashi, Chiaki and Schaerer, Daniel and Adamo, Angela and Fei, Qinyue and Korber, Damien and Matthee, Jorryt J and Marques-Chaves, Rui and Martinez, Zorayda and Mcquinn, Kristen B.W. and Muñoz, Julian B. and Oesch, Pascal A. and Saldana-Lopez, Alberto and Stark, Daniel P. and Stephenson, Mabel G. and Hsiao, Tiger Yu Yang}, issn = {1538-4357}, journal = {The Astrophysical Journal}, number = {2}, publisher = {IOP Publishing}, title = {{A fleeting GLIMPSE of N/O enrichment at cosmic dawn: Evidence for Wolf Rayet N stars in a z = 6.1 galaxy}}, doi = {10.3847/1538-4357/ae5e4c}, volume = {1003}, year = {2026}, } @article{21934, abstract = {An accurate characterisation of the physical properties of galaxies at cosmic dawn is key to understanding the origin of the high abundance of UV-bright galaxies at z≳10. We exploit deep (9.1-hour exposure time) NIRSpec PRISM observations of GHZ2 to constrain the sources of ionising radiation and the properties of the interstellar medium (ISM) in this bright, compact, and highly ionising galaxy at z=12.3. We measure with high significance the prominent N IV, C IV, He II, O III, C III, O II, and Ne III emission features previously detected in shallower observations, and confirm the detection of the N III] λ1750 multiplet, yielding tight constraints on the N/O ratio, which is found to be ≃2 times the solar value. We also detect the Mg II λ2800, [Fe IV] λ2833 and Si II λ1812 doublets, the H8+HeI λλ3889 blend, and the Si IV+O IV] λλ1400 absorption complex. The O III λ3133 fluorescence line is only detected in the first observing epoch, implying variability on a rest-frame time span of 19 days, strongly suggesting the presence of an active nucleus. Combining the NIRSpec dataset with available optical and far-infrared constraints from MIRI and ALMA, we show that the emission spectrum of GHZ2 cannot be reproduced by single-density spectro-photometric models, even under extreme assumptions on the ionisation parameter and electron density. Multi-zone photoionisation modelling performed with the HOMERUN code demonstrates that star formation must be occurring in a strongly stratified ISM, where both low-/intermediate-density gas and high-density regions (log(ne/cm−3 ) ≳ 4) coexist. The GHZ2 emission landscape is consistent with either a composite star-formation plus AGN scenario, or with star formation occurring in a combination of radiation- and matter-bounded regions. Purely radiation-bounded stellar models fail to reproduce the observed He II emission, making an additional hard ionising component unavoidable.}, author = {Castellano, M. and Napolitano, L. and Moreschini, B. and Calabrò, A. and Christensen, L. and Llerena, M. and Bakx, T. J.L.C. and Belfiore, F. and Bevacqua, D. and Dickinson, M. and Fontana, A. and Gandolfi, G. and Gasparetto, T. and Marconi, A. and Mascia, Sara and Merlin, E. and Morishita, T. and Nanayakkara, T. and Paris, D. and Pentericci, L. and Pérez-Díaz, B. and Roberts-Borsani, G. and Rojas-Ruiz, S. and Santini, P. and Treu, T. and Vanzella, E. and Vulcani, B. and Wang, X. and Yoon, I. and Zavala, J.}, issn = {2565-6120}, journal = {The Open Journal of Astrophysics}, publisher = {Maynooth Academic Publishing}, title = {{Investigating ionising sources and the complex interstellar medium of GHZ2 at z=12.3}}, doi = {10.33232/001c.160281}, volume = {9}, year = {2026}, } @article{21951, abstract = {The central engines of Little Red Dots (LRDs) may be “black hole stars” (BH*s), early stages of black hole growth characterized by dense gas envelopes. So far, the most direct evidence for BH*s comes from a handful of sources where the host galaxy is completely outshone as suggested by their remarkably steep Balmer breaks. Here we present a novel scheme to disentangle BH*s from their host galaxies assuming that the [O III]5008˚A line arises exclusively from the host. Using a sample of 98 LRDs (z ≈ 2 − 9) with high quality NIRSpec/PRISM spectra, we demonstrate that the hostsubtracted median stack displays a Balmer break > 2× stronger than massive quiescent galaxies, with the rest-optical continuum resembling a blackbody-like SED (Teff ≈ 4050 K, log(Lbol) ≈ 43.9 erg s−1 , Reff ≈ 1300 au). We measure a steep Balmer decrement (Hα/Hβ > 10) and numerous density-sensitive features (e.g., Fe II, He I, O I). These are hallmark signatures of dense gas envelopes, providing population-level evidence that BH*s indeed power LRDs. In the median LRD, BH*s account for ∼ 20% of the UV emission, ∼ 50% at the Balmer break, and ∼ 90% at wavelengths longer than Hα with the remainder arising from the host. BH*s preferentially reside in low-mass galaxies (M⋆ ≈ 108 M⊙) undergoing recent starbursts, as evidenced by extreme emission line EWs (e.g., [O III]5008˚A≈ 1100˚A, C III]≈ 12˚A), thereby favoring BH* origins linked to star-formation. We show V-shaped LRD selections are biased to high BH*/host fractions (≳ 60% at 5500˚A) – less dominant BH*s may be powering JWST’s blue broad-line AGN. We find BH*s are so commonplace and transient (duty cycle ∼ 1%, lifetime ∼ 10 Myrs) that every massive black hole may have once shone as a BH*. }, author = {Sun, Wendy Q. and Naidu, Rohan P. and Matthee, Jorryt J and De Graaff, Anna and Chisholm, John and Greene, Jenny E. and Oesch, Pascal A. and Torralba Torregrosa, Alberto and Hviding, Raphael E. and Brammer, Gabriel and Simcoe, Robert A. and Bose, Sownak and Bouwens, Rychard and Dayal, Pratika and Eilers, Anna Christina and Fei, Qinyue and Furtak, Lukas J. and Gottumukkala, Rashmi and Goulding, Andy and Heintz, Kasper E. and Hirschmann, Michaela and Kokorev, Vasily and Leja, Joel and Liu, Zhaoran and Natarajan, Priyamvada and Santarelli, Andrew D. and Setton, David J. and Smith, Aaron and Tacchella, Sandro and Volonteri, Marta and Walter, Fabian and Weibel, Andrea and Williams, Christina C.}, issn = {2565-6120}, journal = {The Open Journal of Astrophysics}, publisher = {Maynooth Academic Publishing}, title = {{Little Red Dot - Host Galaxy = Black Hole Star: A gas-enshrouded heart at the center of every Little Red Dot}}, doi = {10.33232/001c.162505}, volume = {9}, year = {2026}, } @article{21045, abstract = {The abundant population of little red dots (LRDs), compact objects with red UV to optical colors and broad Balmer lines at high redshift, is revealing new insights into the properties of early active galactic nuclei (AGN). Perhaps the most surprising features of this population are the presence of Balmer absorption and ubiquitous strong Balmer breaks. Recent models link these features to an active supermassive black hole (SMBH) cocooned in very dense gas (NH ∼ 1024 cm−2). We present a stringent test of such models using VLT/MUSE observations of A2744-45924, the most luminous LRD known to date (LHα ≈ 1044 erg s−1), located behind the Abell-2744 lensing cluster at z = 4.464 (μ = 1.8). We detect a moderately extended Lyα nebula (h ≈ 5.7 pkpc), spatially offset from the point-like Hα seen by JWST by ≈1.6 pkpc. The Lyα emission is narrow (FWHM = 270 ± 15 km s−1), and faint (Lyα = 0.07Hα) compared to Lyα nebulae typically observed around quasars of similar luminosity. We detect compact N IV]λ1486 emission, spatially aligned with Hα, and a spatial shift in the far-UV continuum matching the Lyα offset. We discuss that Hα and Lyα have distinct physical origins: Hα originates from the AGN, while Lyα is powered by star formation. In the environment of A2744-45924, we identified four extended Lyα halos (Δz < 0.02, Δr < 100 pkpc). Their Lyα luminosities match the expectations based on Hα emission, and show no evidence for radiation from A2744-45924 affecting its surroundings. The lack of strong, compact, and broad Lyα and the absence of a luminous extended halo, suggest that the UV AGN light is obscured by dense gas cloaking the SMBH with a covering factor close to unity.}, author = {Torralba Torregrosa, Alberto and Matthee, Jorryt J and Pezzulli, Gabriele and Urrutia, Tanya and Gronke, Max and Mascia, Sara and D’Eugenio, Francesco and Di Cesare, Claudia and Eilers, Anna Christina and Greene, Jenny E. and Iani, Edoardo and Ishikawa, Yuzo and Mackenzie, Ruari and Naidu, Rohan P. and Navarrete, Benjamín and Kotiwale, Gauri}, issn = {1432-0746}, journal = {Astronomy & Astrophysics}, publisher = {EDP Sciences}, title = {{A weak Ly α halo for an extremely bright little red dot. Indications of enshrouded supermassive black hole growth}}, doi = {10.1051/0004-6361/202555596}, volume = {705}, year = {2026}, }