Satellite quenching, Galaxy inner density and the halo environment

Abstract

Using the Sloan Digital Sky Survey, we adopt the specific star formation rate (sSFR)–Σ*,1kpc diagram as a diagnostic tool to understand quenching in different environments. sSFR is the specific star formation rate and Σ*,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–Σ*,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, Σ*,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* = 109.75–10 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's field quenching track versus the cluster quenching track. These environmental effects in the sSFR–Σ*,1kpc diagram are most significant in our lowest mass range (9.75 < log M*/M⊙ < 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 Σ*,1kpc than the star-forming population. These results indicate that either Σ*,1kpc increases (subsequent to satellite quenching), or Σ*,1kpc for individual galaxies remains unchanged, but the original M* or the time of quenching is significantly different from those now in the GV.