Kavli Affiliate: Roberto Maiolino
| First 5 Authors: Seunghwan Lim, Sandro Tacchella, Roberto Maiolino, Joop Schaye, Matthieu Schaller
| Summary:
Exploiting a large sample of 5.3 million galaxies with
$M_ast,{=},10^{10-11},{rm M}_odot$ from the highest-resolution FLAMINGO
simulation, we carry out a statistical analysis of quiescent and star-forming
galaxies to explore quenching mechanisms. From redshift $z,{simeq},7$ to 0,
we find that the median star-formation rate of main-sequence galaxies is
independent of the environment and of whether a galaxy is a central or
satellite, whereas the fraction of quiescent galaxies is highly sensitive to
both. By employing Random Forest (RF) classifiers, we demonstrate that black
hole (BH) feedback is the most responsible quenching mechanism for both
centrals and satellites, while halo mass is the second most significant. For
satellites, a notable importance given by RF to stellar mass implies in-situ
pre-quenching rather than ex-situ preprocessing prior to infall to the current
host halo. In the cosmic afternoon of $z,{=},$0–1, we identify two distinct
regimes of evolution: at $M_{rm BH},{gtrsim},10^7,{rm M}_odot$,
essentially all galaxies are quenched regardless of their environment; at
$M_{rm BH},{lesssim},10^7,{rm M}_odot$, quenching is determined mainly
by halo mass. Galaxies undergo a sharp transition from the main sequence to
quiescence once their BH mass reaches $M_{rm BH},{simeq},10^7,{rm
M}_odot$ (typically when $M_ast,{simeq},10^{10.5},{rm M}_odot$ and
$M_{rm h},{simeq},10^{12},{rm M}_odot$) with a short quenching timescale
of ${<}$1 Gyr. This transition is driven by a sudden change in the gas mass in
the inner circum-galactic medium. Our results indicate that galaxy quenching
arises from a combination of in-situ and ex-situ physical processes.
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