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Are the ultra-high-redshift galaxies at z > 10 surprising in the context of standard galaxy formation models?

2026-05-14T11:49:10Z

Title: Are the ultra-high-redshift galaxies at z > 10 surprising in the context of standard galaxy formation models? Authors: Yung, L. Y. Aaron; Somerville, Rachel S.; Finkelstein, Steven L.; Wilkins, Stephen M.; Gardner, Jonathan P. Abstract: A substantial number of ultra-high redshift (8 ≲ z ≲ 17) galaxy candidates have been detected with JWST, posing the question: Are these observational results surprising in the context of current galaxy formation models? We address this question using the well-established Santa Cruz semi-analytic models, implemented within merger trees from the new suite of cosmological N-body simulations gureft, which were carefully designed for ultra-high redshift studies. Using our fiducial models calibrated at z = 0, we present predictions for stellar mass functions, rest-frame UV luminosity functions, and various scaling relations. We find that our (dust-free) models predict galaxy number densities at z ∼ 11 (z ∼ 13) that are an order of magnitude (a factor of ∼30) lower than the observational estimates. We estimate the uncertainty in the observed number densities due to cosmic variance, and find that it leads to a fractional error of ∼20–30 per cent at z = 11 (∼30–80 per cent at z = 14) for a 100 arcmin2 field. We explore which processes in our models are most likely to be rate-limiting for the formation of luminous galaxies at these early epochs, considering the halo formation rate, gas cooling, star formation, and stellar feedback, and conclude that it is mainly efficient stellar-driven winds. We find that a modest boost of a factor of ∼4 to the UV luminosities, which could arise from a top-heavy stellar initial mass function, would bring our current models into agreement with the observations. Adding a stochastic component to the UV luminosity can also reconcile our results with the observations.

CEERS key paper. V. galaxies at 4< z< 9 are bluer than they appear–characterizing galaxy stellar populations from rest-frame∼ 1 μ m imaging

2026-05-13T11:40:25Z

Title: CEERS key paper. V. galaxies at 4< z< 9 are bluer than they appear–characterizing galaxy stellar populations from rest-frame∼ 1 μ m imaging Authors: Papovich, Casey; Cole, Justin W.; Yang, Guang; Finkelstein, Steven L.; Barro, Guillermo; Buat, Véronique; Burgarella, Denis; Pérez-González, Pablo G.; Santini, Paola; Seillé, Lise-Marie; Shen, Lu; Haro, Pablo Arrabal; Bagley, Micaela B.; Bell, Eric F.; Bisigello, Laura; Calabrò, Antonello; Casey, Caitlin M.; Castellano, Marco; Chworowsky, Katherine; Cleri, Nikko J.; Costantin, Luca; Cooper, M. C.; Dickinson, Mark; Ferguson, Henry C.; Fontana, Adriano; Giavalisco, Mauro; Grazian, Andrea; Grogin, Norman A.; Hathi, Nimish P.; Holwerda, Benne W.; Hutchison, Taylor A.; Kartaltepe, Jeyhan S.; Kewley, Lisa J.; Kirkpatrick, Allison; Kocevski, Dale D.; Koekemoer, Anton M.; Larson, Rebecca L.; Long, Arianna S.; Lucas, Ray A.; Pentericci, Laura; Pirzkal, Nor; Ravindranath, Swara; Somerville, Rachel S.; Trump, Jonathan R.; Urbano Stawinski, Stephanie M.; Weiner, Benjamin J.; Wilkins, Stephen M.; Yung, L. Y. Aaron; Zavala, Jorge A. Abstract: We present results from the Cosmic Evolution Early Release Survey on the stellar population parameters for 28 galaxies with redshifts 4 < z < 9 using imaging data from the James Webb Space Telescope (JWST) Mid-Infrared Instrument (MIRI) combined with data from the Hubble Space Telescope and the Spitzer Space Telescope. The JWST/MIRI 5.6 and 7.7 μm data extend the coverage of the rest-frame spectral energy distribution to nearly 1 μm for galaxies in this redshift range. By modeling the galaxies’ SEDs the MIRI data show that the galaxies have, on average, rest-frame UV (1600 Å)—I-band colors 0.4 mag bluer than derived when using photometry that lacks MIRI. Therefore, the galaxies have lower ratios of stellar mass to light. The MIRI data reduce the stellar masses by dex at 4 < z < 6 and 0.37 dex at 6 < z < 9. This also reduces the star formation rates (SFRs) by 〈ΔlogSFR〉 = 0.14 dex at 4 < z < 6 and 0.27 dex at 6 < z < 9. The MIRI data also improve constraints on the allowable stellar mass formed in early star formation. We model this using a star formation history that includes both a “burst” at zf = 100 and a slowly varying (“delayed-τ”) model. The MIRI data reduce the allowable stellar mass by 0.6 dex at 4 < z < 6 and by ≈1 dex at 6 < z < 9. Applying these results globally, this reduces the cosmic stellar-mass density by an order of magnitude in the early Universe (z ≈ 9). Therefore, observations of rest-frame ≳1 μm are paramount for constraining the stellar-mass buildup in galaxies at very high redshifts.

ALMA FIR view of ultra-high-redshift galaxy candidates at z∼11–17 : blue monsters or low-z red interlopers?

2026-05-12T13:46:47Z

Title: ALMA FIR view of ultra-high-redshift galaxy candidates at z∼11–17 : blue monsters or low-z red interlopers? Authors: Fujimoto, Seiji; Finkelstein, Steven L.; Burgarella, Denis; Carilli, Chris L.; Buat, Véronique; Casey, Caitlin M.; Ciesla, Laure; Tacchella, Sandro; Zavala, Jorge A.; Brammer, Gabriel; Fudamoto, Yoshinobu; Ouchi, Masami; Valentino, Francesco; Cooper, M. C.; Dickinson, Mark; Franco, Maximilien; Giavalisco, Mauro; Hutchison, Taylor A.; Kartaltepe, Jeyhan S.; Koekemoer, Anton M.; Kojima, Takashi; Larson, Rebecca L.; Murphy, E. J.; Papovich, Casey; Pérez-González, Pablo G.; Somerville, Rachel S.; Yoon, Ilsang; Wilkins, Stephen M.; Akins, Hollis; Amorín, Ricardo O.; Haro, Pablo Arrabal; Bagley, Micaela B.; Chworowsky, Katherine; Cleri, Nikko J.; Cooper, Olivia R.; Costantin, Luca; Daddi, Emanuele; Ferguson, Henry C.; Jiménez-Andrade, E. F.; Juneau, Stéphanie; Kirkpatrick, Allison; Kocevski, Dale D.; Le Bail, Aurélien; Long, Arianna; Lucas, Ray A.; Magnelli, Benjamin; McKinney, Jed; Rose, Caitlin; Seillé, Lise-Marie; Simons, Raymond C.; Weiner, Benjamin J.; Yung, L. Y. Aaron Abstract: We present Atacama Large Millimeter/submillimeter Array (ALMA) Band 7 observations of a remarkably bright galaxy candidate at (MUV = −21.6), S5-z17-1, identified in James Webb Space Telescope (JWST) Early Release Observation data of Stephen’s Quintet. We do not detect the dust continuum at 866 μm, ruling out the possibility that S5-z17-1 is a low-z dusty starburst with a star formation rate of ≳30 M⊙ yr−1. We detect a 5.1σ line feature at 338.726 ± 0.007 GHz exactly coinciding with the JWST source position, with a 2% likelihood of the signal being spurious. The most likely line identification would be [O iii]52 μm at z = 16.01 or [C ii]158 μm at z = 4.61, whose line luminosities do not violate the nondetection of the dust continuum in both cases. Together with three other z ≳ 11–13 candidate galaxies recently observed with ALMA, we conduct a joint ALMA and JWST spectral energy distribution (SED) analysis and find that the high-z solution at z ∼ 11–17 is favored in every candidate as a very blue (UV continuum slope of ≃−2.3) and luminous (MUV ≃ [ − 24:−21]) system. Still, we find in several candidates that reasonable SED fits (Δχ2 ≲ 4) are reproduced by type II quasar and/or quiescent galaxy templates with strong emission lines at z ∼ 3–5, where such populations predicted from their luminosity functions and EW([O iii]+Hβ) distributions are abundant in survey volumes used for the identification of the z ∼ 11–17 candidates. While these recent ALMA observation results have strengthened the likelihood of the high-z solutions, lower-z possibilities are not completely ruled out in several of the z ∼ 11–17 candidates, indicating the need to consider the relative surface densities of the lower-z contaminants in the ultra-high-z galaxy search.

CEERS key paper. II. A first look at the resolved host properties of AGN at 3< z< 5 with JWST

2026-05-11T14:11:22Z

Title: CEERS key paper. II. A first look at the resolved host properties of AGN at 3< z< 5 with JWST Authors: Kocevski, Dale D.; Barro, Guillermo; McGrath, Elizabeth J.; Finkelstein, Steven L.; Bagley, Micaela B.; Ferguson, Henry C.; Jogee, Shardha; Yang, Guang; Dickinson, Mark; Hathi, Nimish P.; Backhaus, Bren E.; Bell, Eric F.; Bisigello, Laura; Buat, Véronique; Burgarella, Denis; Casey, Caitlin M.; Cleri, Nikko J.; Cooper, M. C.; Costantin, Luca; Croton, Darren; Daddi, Emanuele; Fontana, Adriano; Fujimoto, Seiji; Gardner, Jonathan P.; Gawiser, Eric; Giavalisco, Mauro; Grazian, Andrea; Grogin, Norman A.; Guo, Yuchen; Haro, Pablo Arrabal; Hirschmann, Michaela; Holwerda, Benne W.; Huertas-Company, Marc; Hutchison, Taylor A.; Iyer, Kartheik G.; Jones, Brenda; Juneau, Stéphanie; Kartaltepe, Jeyhan S.; Kewley, Lisa J.; Kirkpatrick, Alison; Koekemoer, Anton M.; Kurczynski, Peter; Bail, Aurélien Le; Long, Arianna S.; Lotz, Jennifer M.; Lucas, Ray A.; Papovich, Casey; Pentericci, Laura; Pérez-González, Pablo G.; Pirzkal, Nor; Rafelski, Marc; Ravindranath, Swara; Somerville, Rachel S.; Straughn, Amber N.; Tacchella, Sandro; Trump, Jonathan R.; Wilkins, Stephen M.; Wuyts, Stijn; Yung, L. Y. Aaron; Zavala, Jorge A. Abstract: We report on the host properties of five X-ray-luminous active galactic nuclei (AGN) identified at 3 < z < 5 in the first epoch of imaging from the Cosmic Evolution Early Release Science Survey. Each galaxy has been imaged with the JWST Near-Infrared Camera, which provides rest-frame optical morphologies at these redshifts. We also derive stellar masses and star formation rates for each host by fitting its spectral energy distribution using a combination of galaxy and AGN templates. We find that three of the AGN hosts have spheroidal morphologies, one is a bulge-dominated disk, and one is dominated by pointlike emission. None are found to show strong morphological disturbances that might indicate a recent interaction or merger event. When compared to a sample of mass-matched inactive galaxies, we find that the AGN hosts have morphologies that are less disturbed and more bulge-dominated. Notably, all four of the resolved hosts have rest-frame optical colors consistent with a quenched or poststarburst stellar population. The presence of AGN in passively evolving galaxies at z > 3 is significant because a rapid feedback mechanism is required in most semianalytic models and cosmological simulations to explain the growing population of massive quiescent galaxies observed at these redshifts. Our findings show that AGN can continue to inject energy into these systems after their star formation is curtailed, potentially heating their halos and preventing renewed star formation. Additional observations will be needed to determine what role this feedback may play in helping to quench these systems and/or maintain their quiescent state.