Two Conditions for Galaxy Quenching: Compact Centres and Massive Haloes

TL;DR

This study explores how galaxy quenching is influenced by central compactness and halo mass, revealing different dominant mechanisms for centrals and satellites and proposing a model where compactness causes rapid quenching and halo mass causes slow quenching.

Contribution

It identifies the distinct roles of compact centres and halo mass in galaxy quenching, and introduces a semi-analytic model explaining their combined effects.

Findings

Quenched fraction correlates strongly with central compactness at certain ranges.

Halo mass influences quenching by shifting star formation rates without changing distribution shape.

Rapid quenching linked to central compactness; slow quenching linked to halo mass.

Abstract

We investigate the roles of two classes of quenching mechanisms for central and satellite galaxies in the SDSS ($z<0.075$): those involving the halo and those involving the formation of a compact centre. For central galaxies with inner compactness $\Sigma_{\rm 1kpc} \sim 10^{9-9.4}M_{\odot} {\rm kpc}^{-2}$, the quenched fraction $f_{q}$ is strongly correlated with $\Sigma_{\rm 1kpc}$ with only weak halo mass $M_{\rm h}$ dependence. However, at higher and lower $\Sigma_{\rm 1kpc}$, sSFR is a strong function of $M_{\rm h}$ and mostly independent of $\Sigma_{\rm 1kpc}$. In other words, $\Sigma_{\rm 1kpc} \sim 10^{9-9.4} M_{\odot} {\rm kpc}^{-2}$ divides galaxies into those with high sSFR below and low sSFR above this range. In both the upper and lower regimes, increasing $M_{\rm h}$ shifts the entire sSFR distribtuion to lower sSFR without a qualitative change in shape. This is true even at fixed $M_{*}$, but varying $M_{*}$ at fixed $M_{\rm h}$ adds no quenching information. Most of the quenched centrals with $M_{\rm h} > 10^{11.8}M_{\odot}$ are dense ($\Sigma_{\rm 1kpc} > 10^{9}~ M_{\odot} {\rm kpc}^{-2}$), suggesting compaction-related quenching maintained by halo-related quenching. However, 21% are diffuse, indicating only halo quenching. For satellite galaxies in the outskirts of halos, quenching is a strong function of compactness and a weak function of host $M_{\rm h}$. In the inner halo, $M_{\rm h}$ dominates quenching, with $\sim 90\%$ of the satellites being quenched once $M_{\rm h} > 10^{13}M_{\odot}$. This regional effect is greatest for the least massive satellites. As demonstrated via semi-analytic modelling with simple prescriptions for quenching, the observed correlations can be explained if quenching due to central compactness is rapid while quenching due to halo mass is slow.