Satellite quenching, Galaxy inner density and the halo environment

Abstract

Using the Sloan Digital Sky Survey, we adopt the specific star formation rate (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 characterized 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&apos;. 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 &apos;green valley&apos; or GV) decreases smoothly with the environment by as much as 0.2 dex for M-* = 10(9.75-10) from the field, and decreasing for satellites in larger haloes and at smaller radial distances within same-mass haloes. We interpret this shift as indicating the relative importance of today&apos;s field quenching track versus the cluster quenching track. These environmental effects in the sSFR-Sigma(*), 1kpc diagram are most significant in our lowest mass range (9.75 < logM(*)/M-circle dot < 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 starforming 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.