In-situ vs. ex-situ drivers of galaxy quenching: critical black hole mass and main sequence universality in the FLAMINGO simulation

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Main Authors: Lim, Seunghwan, Tacchella, Sandro, Maiolino, Roberto, Schaye, Joop, Schaller, Matthieu
Format: Preprint
Published: 2025
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author Lim, Seunghwan
Tacchella, Sandro
Maiolino, Roberto
Schaye, Joop
Schaller, Matthieu
author_facet Lim, Seunghwan
Tacchella, Sandro
Maiolino, Roberto
Schaye, Joop
Schaller, Matthieu
contents 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.
format Preprint
id arxiv_https___arxiv_org_abs_2504_02027
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle In-situ vs. ex-situ drivers of galaxy quenching: critical black hole mass and main sequence universality in the FLAMINGO simulation
Lim, Seunghwan
Tacchella, Sandro
Maiolino, Roberto
Schaye, Joop
Schaller, Matthieu
Astrophysics of Galaxies
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.
title In-situ vs. ex-situ drivers of galaxy quenching: critical black hole mass and main sequence universality in the FLAMINGO simulation
topic Astrophysics of Galaxies
url https://arxiv.org/abs/2504.02027