Exploring over 700 massive quiescent galaxies at z = 2-7: Demographics and stellar mass functions

TL;DR

This study analyzes over 700 massive quiescent galaxies at redshifts 2-7 using JWST data, revealing discrepancies with models and highlighting the evolution of galaxy quenching and stellar mass functions in the early universe.

Contribution

It provides the largest sample to date of high-redshift quiescent galaxies, reports their number densities and mass functions, and challenges existing galaxy formation models.

Findings

Significant overabundance of massive quiescent galaxies compared to models.

No current models accurately reproduce the stellar mass functions at z=2-5.

Steep increase in cosmic stellar mass density for quiescent galaxies from z=2 to 7.

Abstract

High-redshift ($z>2$) massive quiescent galaxies are crucial tests of early galaxy formation and evolutionary mechanisms through their cosmic number densities and stellar mass functions (SMFs). We explore a sample of 743 massive ($\rm M_*> 10^{9.5}M_\odot$) quiescent galaxies from $z=2-7$ in over 800 arcmin$^2$ of NIRCam imaging from a compilation of public JWST fields (with a total area $>$ 5 $\times$ previous JWST studies). We compute and report their cosmic number densities, stellar mass functions, and cosmic stellar mass density. We confirm a significant overabundance of massive quiescent galaxies relative to a range of cosmological hydrodynamical simulations and semi-analytic models (SAMs). We find that no simulations or SAMs accurately reproduce the SMF for massive quiescent galaxies at any redshift within the interval $z=2-5$. This shows that none of these models' feedback prescriptions are fully capturing high-z galaxy quenching, challenging the standard formation scenarios. We find a greater abundance of lower-mass ($\rm M_*<10^{10}M_\odot$) quiescent galaxies than previously found, highlighting the importance of sSFR cuts rather than simple colour selection. We show the importance of this selection bias, alongside individual field-to-field variations caused by cosmic variance, in varying the observed quiescent galaxy SMF, especially at higher-z. We also find a steeper increase in the cosmic stellar mass density for massive quiescent galaxies than has been seen previously, with $\rho_*\propto (1+z)^{-7.2\pm0.3}$, indicating the dramatic increase in the importance of galaxy quenching within these epochs.