Satellite Quenching, Galaxy Inner Density and the Halo Environment

TL;DR

This study uses SDSS data to analyze how galaxy quenching relates to inner density and environment, revealing smooth variations in star formation and density with environmental factors, especially in low-mass galaxies.

Contribution

It introduces the sSFR-$ Sigma_{1kpc}$ diagram as a diagnostic tool to connect galaxy quenching with environment, highlighting the role of inner density and environment in galaxy evolution.

Findings

Star-forming galaxy sSFR decreases with environment

Transition galaxy inner density decreases in denser environments

Quenched galaxies have higher inner density than star-forming ones

Abstract

Using the Sloan Digital Sky Survey, we adopt the sSFR-$\Sigma_{1kpc}$ diagram as a diagnostic tool to understand quenching in different environments. sSFR is the specific star formation rate, and $\Sigma_{1kpc}$ is the stellar surface density in the inner kpc. Although both the host halo mass and group-centric distance affect the satellite population, we find that these can be characterised by a single number, the quenched fraction, such that key features of the sSFR-$\Sigma_{1kpc}$ diagram vary smoothly with this proxy for the "environment". Particularly, the sSFR of star-forming galaxies decreases smoothly with this quenched fraction, the sSFR of satellites being 0.1 dex lower than in the field. Furthermore, $\Sigma_{1kpc}$ of the transition galaxies (i.e., the "green valley" or GV) decreases smoothly with the environment, by as much as 0.2 dex for $M_* = 10^{9.75-10} M_{\odot}$ from the field, and decreasing for satellites in larger halos and at smaller radial distances within same-mass halos. We interpret this shift as indicating the relative importance of today's field quenching track vs. the cluster quenching track. These environmental effects in the sSFR-$\Sigma_{1kpc}$ diagram are most significant in our lowest mass range ($9.75 < \log M_{*}/M_{\odot} < 10$). One feature that is shared between all environments is that at a given $M_{*}$ quenched galaxies have about 0.2-0.3 dex higher $\Sigma_{1kpc}$ than the star-forming population. These results indicate that either $\Sigma_{1kpc}$ increases (subsequent to satellite quenching), or $\Sigma_{1kpc}$ for individual galaxies remains unchanged, but the original $M_*$ or the time of quenching is significantly different from those now in the GV.