Kavli Affiliate: Roberto Maiolino
| First 5 Authors: William M. Baker, Seunghwan Lim, Francesco D’Eugenio, Roberto Maiolino, Zhiyuan Ji
| Summary:
We use NIRSpec/MSA spectroscopy and NIRCam imaging to study a sample of 18
massive ($log; M_{*}/M_{odot} gt 10;$dex), central quiescent galaxies at
$2leq z leq 5$ in the GOODS fields, to investigate their number density,
star-formation histories, quenching timescales, and incidence of AGN. The data
depth reaches $log M_*/M_odot approx 9;$dex, yet the least-massive central
quiescent galaxy found has $log M_*/M_odot gt 10;$dex, suggesting that
quenching is regulated by a physical quantity that scales with $M_*$. With
spectroscopy, we assess the completeness and purity of photometric samples,
finding number densities 10 times higher than predicted by galaxy formation
models, confirming earlier photometric studies. We compare our number densities
to predictions from FLAMINGO, the largest-box full-hydro simulation suite to
date. We rule out cosmic variance at the 3-$sigma$ level, providing
spectroscopic confirmation that galaxy formation models do not match
observations at $z>3$. Using FLAMINGO, we find that the vast majority of
quiescent galaxies’ stars formed in situ, with these galaxies not having
undergone multiple major dry mergers. This is in agreement with the compact
observed size of these systems and suggests that major mergers are not a viable
channel for quenching most massive galaxies. Several of our observed galaxies
are old, with four galaxies displaying 4000-r{A} breaks with formation and
quenching redshifts of $zgeq8$ and $zgeq6$. Using tracers, we find that 8
galaxies host AGN, including old systems suggesting a high AGN duty cycle with
a continuing trickle of gas to fuel accretion.
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