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 depth
of our data 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 as benchmark, 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 particularly old, with four galaxies displaying 4000-r{A} breaks;
full-spectrum fitting infers formation and quenching redshifts of $zgeq8$ and
$zgeq6$. Using all available AGN tracers, we find that 8 massive quiescent
galaxies host AGN, including in old systems. This suggests a high duty cycle of
AGN and a continued trickle of gas to fuel accretion.
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