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1. Little Red Dots on FIRE: The Ability of Bursty Galaxies to Host an Abundant Population of High-redshift AGN

   https://doi.org/10.3847/2041-8213/ae5d45  

   Marszewski, Andrew; Faucher-Giguère, Claude-André; Sun, Guochao; Anglés-Alcázar, Daniel; Feldmann, Robert; Su, Kung-Yi; Miller, Tim B; Roy, Niranjan Chandra (April 2026, The Astrophysical Journal Letters)

   Abstract The James Webb Space Telescope has unveiled an abundant population of potential active galactic nuclei (AGN) at high redshift (z ≳ 4) known as little red dots (LRDs), which are likely hosted in relatively low-mass galaxies. However, previous theoretical models have highlighted the difficulty in continuously feeding massive black holes in the central regions of bursty, high-redshift galaxies because of repeated gas evacuation by stellar feedback. We analyze galaxies in high-redshift FIRE-2 simulations to understand whether they are capable of hosting the observed abundant population of high-redshift AGN. We use a gravitational torque-driven accretion (GTDA) model and a simple freefall accretion model to derive black hole accretion rates and construct predicted AGN bolometric luminosity functions forz = 5–7. The GTDA model and the freefall model with black holes accreting ≲1% of their central gas supply (<100 pc) per freefall time predict AGN abundances that are more than sufficient to explain the most recent LRD observations. The fiducial models, in fact, overpredict the number of low-luminosity AGN as compared with observations. We explore possible resolutions of this tension. A plausible, though likely not unique, scenario for alleviating the AGN overpredictions, which also provides a good match to the host-galaxy UV luminosity distribution, suggests that LRDs are super-Eddington-accreting, Eddington-luminosity-limited,M_BH ≳ 2 × 10⁵M_⊙black holes residing inM_⋆ ≳ 2 × 10⁷M_⊙galaxies. We show that, under simple assumptions, mock observations of such sources can reproduce key observed LRD characteristics. 

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2. Little Red Dots as Globular Clusters in Formation

   https://doi.org/10.3847/2041-8213/ae6dae  

   Chisholm, John; Berg, Danielle A; Boylan-Kolchin, Michael; de_Graaff, Anna; Furtak, Lukas J; Kokorev, Vasily; Matthee, Jorryt; Muñoz, Julian B; Naidu, Rohan P; Sander, Andreas_A C (June 2026, The Astrophysical Journal Letters)

   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 LRDz ∼ 5−7 UV luminosity function naturally evolves, under standard evolutionary and mass-loss prescriptions, into a present-day mass function with a turnover at ${\log }_{10}($ 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. 

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3. Cross-correlation of Luminous Red Galaxies with Machine Learning Selected Active Galactic Nuclei in HSC-SSP: Unobscured AGN Residing in More Massive Halos

   https://doi.org/10.3847/1538-4357/ad8342  

   Córdova_Rosado, Rodrigo; Goulding, Andy D; Greene, Jenny E; Petter, Grayson C; Hickox, Ryan C; Kokron, Nickolas; Strauss, Michael A; Givans, Jahmour J; Toba, Yoshiki; Henderson, Cassandra Starr (December 2024, The Astrophysical Journal)

   Abstract Active galactic nuclei (AGN) are the signposts of black hole growth, and likely play an important role in galaxy evolution. An outstanding question is whether AGN of different spectral types indicate different evolutionary stages in the coevolution of black holes and galaxies. We present the angular correlation function between an AGN sample selected from Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) optical photometry and Wide-field Infrared Survey Explorer mid-IR photometry and a luminous red galaxy (LRG) sample from HSC-SSP. We investigate AGN clustering strength as a function of luminosity and spectral features across three independent HSC fields totaling ∼600 deg², forz∈ 0.6 −1.2 and AGN withL_6μm> 3 × 10⁴⁴erg s⁻¹. There are ∼28,500 AGN and ∼1.5 million LRGs in our primary analysis. We determine the average halo mass for the full AGN sample (M_h≈ 10^12.9h⁻¹M_⊙), and note that it does not evolve significantly as a function of redshift (over this narrow range) or luminosity. We find that, on average, unobscured AGN (M_h≈ 10^13.3h⁻¹M_⊙) occupy ∼4.5× more massive halos than obscured AGN (M_h≈ 10^12.6h⁻¹M_⊙), at 5σstatistical significance using 1D uncertainties, and at 3σusing the full covariance matrix, suggesting a physical difference between unobscured and obscured AGN, beyond the line-of-sight viewing angle. Furthermore, we find evidence for a halo mass dependence on reddening level within the Type I AGN population, which could support the existence of a dust-obscured phase. However, we also find that quite small systematic shifts in the redshift distributions of the AGN sample could explain current and previously observed differences inM_h. 

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4. COSMOS-Web: Intrinsically Luminous z ≳ 10 Galaxy Candidates Test Early Stellar Mass Assembly

   https://doi.org/10.3847/1538-4357/ad2075  

   Casey, Caitlin M; Akins, Hollis B; Shuntov, Marko; Ilbert, Olivier; Paquereau, Louise; Franco, Maximilien; Hayward, Christopher C; Finkelstein, Steven L; Boylan-Kolchin, Michael; Robertson, Brant E; et al (April 2024, The Astrophysical Journal)

   Abstract We report the discovery of 15 exceptionally luminous 10 ≲z≲ 14 candidate galaxies discovered in the first 0.28 deg²of JWST/NIRCam imaging from the COSMOS-Web survey. These sources span rest-frame UV magnitudes of −20.5 >M_UV> −22, and thus constitute the most intrinsically luminousz≳ 10 candidates identified by JWST to date. Selected via NIRCam imaging, deep ground-based observations corroborate their detection and help significantly constrain their photometric redshifts. We analyze their spectral energy distributions using multiple open-source codes and evaluate the probability of low-redshift solutions; we conclude that 12/15 (80%) are likely genuinez≳ 10 sources and 3/15 (20%) likely low-redshift contaminants. Three of ourz∼ 12 candidates push the limits of early stellar mass assembly: they have estimated stellar masses ∼ 5 × 10⁹M_⊙, implying an effective stellar baryon fraction ofϵ_⋆∼ 0.2−0.5, whereϵ_⋆≡M_⋆/(f_bM_halo). The assembly of such stellar reservoirs is made possible due to rapid, burst-driven star formation on timescales < 100 Myr where the star formation rate may far outpace the growth of the underlying dark matter halos. This is supported by the similar volume densities inferred forM_⋆∼ 10¹⁰M_⊙galaxies relative toM_⋆∼ 10⁹M_⊙—both about 10⁻⁶Mpc⁻³—implying they live in halos of comparable mass. At such high redshifts, the duty cycle for starbursts would be of order unity, which could cause the observed change in the shape of the UV luminosity function from a double power law to a Schechter function atz≈ 8. Spectroscopic redshift confirmation and ensuing constraints of their masses will be critical to understand how, and if, such early massive galaxies push the limits of galaxy formation in the Lambda cold dark matter paradigm. 

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5. Rise of the Forsaken Relics: Connecting Present-day Stellar Streams and Phase-mixed Galaxies to the Epoch of Reionization

   https://doi.org/10.3847/1538-4357/ae32eb  

   Kundu, Aritra; Sanderson, Robyn; Lidz, Adam; Gandhi, Pratik J; Wetzel, Andrew; Feldmann, Robert; Panithanpaisal, Nondh; Singh, Jasjeev; Boylan-Kolchin, Michael (February 2026, The Astrophysical Journal)

   The “near–far” approach to studying reionization leverages the star formation histories of the Milky Way (MW) or Local Group (LG) galaxies, derived from resolved photometry, to infer the low-mass/faint end of the stellar mass functions (SMFs) or the ultraviolet luminosity functions (UVLFs) of high-redshift galaxies (z≳ 6), beyond the current James Webb Space Telescope detection limits (M_UV≳ −15). Previous works considered only intact low-mass galaxies in the MW and LG, neglecting disrupted galaxies such as stellar streams and phase-mixed objects. Using the FIRE-2 simulations, we show that these disrupted galaxies contribute up to ∼50% of the total stellar-mass budget of the proto-MW/LG atz= 6−9. Including all the progenitors of these disrupted galaxies improves the normalization of the recovered SMFs/UVLFs by factors of ∼2–3 and reduces the halo-to-halo variation in the slope by ∼20%–40%. This enables robust constraints down to at least the resolution limit of the simulations, nearM_⋆∼ 10⁵M_⊙orM_UV∼ −10 atz≳ 6. We also show that “fossil-record” reconstructions—which assume each present-day system descends from a single reionization-era progenitor—are sensitive to the stellar-mass/UV-magnitude thresholds, which introduces bias in the inferred slopes at the low-mass/faint end. Additionally, we demonstrate that neglecting disrupted systems underestimates the contribution of galaxies withM_UV≲ −15 to the reionization-era UV luminosity density. Finally, we estimate that a significant fraction (∼50%) of streams withM_⋆≳ 10⁶M_⊙atz= 0 should be detectable from upcoming Rubin Observatory and Roman Space Telescope observations. 

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