3 research outputs found
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Extreme value statistics of the halo and stellar mass distributions at high redshift: are JWST results in tension with ?CDM?
The distribution of dark matter halo masses can be accurately predicted in the lambda cold dark matter (?CDM) cosmology. The presence of a single massive halo or galaxy at a particular redshift, assuming some baryon and stellar fraction for the latter, can therefore be used to test the underlying cosmological model. A number of recent measurements of very large galaxy stellar masses at high redshift (z > 8) motivate an investigation into whether any of these objects are in tension with ?CDM. We use extreme value statistics to generate confidence regions in the mass–redshift plane for the most extreme mass haloes and galaxies. Tests against numerical models show no tension, neither in their dark matter halo masses nor their galaxy stellar masses. However, we find tentative >3s tension with recent observational determinations of galaxy masses at high redshift from both Hubble Space Telescope and James Webb Space Telescope, despite using conservative estimates for the stellar fraction (f* ~ 1). Either these galaxies are in tension with ?CDM, or there are unaccounted for uncertainties in their stellar mass or redshift estimates
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ALMA FIR view of ultra-high-redshift galaxy candidates at z ∼ 11-17: blue monsters or low-z red interlopers?
We present Atacama Large Millimeter/submillimeter Array (ALMA) Band 7 observations of a remarkably bright galaxy candidate at z phot = 16.7 − 0.3 + 1.9 (M UV = −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 (M UV ≃ [ − 24:−21]) system. Still, we find in several candidates that reasonable SED fits (Δχ 2 ≲ 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.</p
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On the stellar populations of galaxies at z = 9-11: the growth of metals and stellar mass at early times
We present a detailed stellar population analysis of 11 bright (H < 26.6) galaxies at z = 9-11 (three spectroscopically confirmed) to constrain the chemical enrichment and growth of stellar mass of early galaxies. We use the flexible Bayesian spectral energy distribution (SED) fitting code Prospector with a range of star formation histories (SFHs), a flexible dust attenuation law, and a self-consistent model of emission lines. This approach allows us to assess how different priors affect our results and how well we can break degeneracies between dust attenuation, stellar ages, metallicity, and emission lines using data that probe only the rest-frame ultraviolet (UV) to optical wavelengths. We measure a median observed UV spectral slope ß=-1.87-0.43+0.35 for relatively massive star-forming galaxies ( 9 10