Mass and Environment as Drivers of Galaxy Evolution. II. The Quenching of Satellite Galaxies as the Origin of Environmental Effects

We extend the phenomenological study of the evolving galaxy population of Peng et al. (2010) to the central/satellite dichotomy in Yang et al. Sloan Digital Sky Survey (SDSS) groups. We find that satellite galaxies are responsible for all the environmental effects in our earlier work. The fraction of centrals that are red does not depend on their environment but only on their stellar masses, whereas that of the satellites depends on both. We define a relative satellite quenching efficiency ɛ_sat, which is the fraction of blue centrals that are quenched upon becoming the satellite of another galaxy. This is shown to be independent of stellar mass, but to depend strongly on local overdensity, δ, ranging between 0.2 and at least 0.8. The red fraction of satellites correlate much better with the local overdensity δ, a measure of location within the group, than with the richness of the group, i.e., dark matter halo mass. This, and the fact that satellite quenching depends on local density and not on either the stellar mass of the galaxy or the dark matter halo mass, gives clues as to the nature of the satellite-quenching process. We furthermore show that the action of mass quenching on satellite galaxies is also independent of the dark matter mass of the parent halo. We then apply the Peng et al. approach to predict the mass functions of central and satellite galaxies, split into passive and active galaxies, and show that these match very well the observed mass functions from SDSS, further strengthening the validity of this phenomenological approach. We highlight the fact that the observed M* is exactly the same for the star-forming centrals and satellites and the observed M* for the star-forming satellites is independent of halo mass above 10¹² M _⊙, which emphasizes the universality of the mass-quenching process that we identified in Peng et al. Post-quenching merging modifies the mass function of the central galaxies but can increase the mass of typical centrals by only about 25%.