Galaxy evolution in groups and clusters: star formation rates, red
  sequence fractions, and the persistent bimodality
  Using galaxy group/cluster catalogs created from the Sloan Digital Sky Survey
Data Release 7, we examine in detail the specific star formation rate (SSFR)
distribution of satellite galaxies and its dependence on stellar mass, host
halo mass, and halo-centric radius. All galaxies, regardless of
central-satellite designation, exhibit a similar bimodal SSFR distribution,
with a strong break at SSFR ~ 10^-11 yr^-1 and the same high SSFR peak; in no
regime is there ever an excess of galaxies in the `green valley'. Satellite
galaxies are simply more likely to lie on the quenched (`red sequence') side of
the SSFR distribution. Furthermore, the satellite quenched fraction excess
above the field galaxy value is nearly independent of galaxy stellar mass. An
enhanced quenched fraction for satellites persists in groups with halo masses
down to 3 x 10^11 Msol and increases strongly with halo mass and toward halo
center. We find no detectable quenching enhancement for galaxies beyond ~2R_vir
around massive clusters once these galaxies have been decomposed into centrals
and satellites. These trends imply that (1) galaxies experience no significant
environmental effects until they cross within ~R_vir of a more massive host
halo, (2) after this, star formation in active satellites continues to evolve
in the same manner as active central galaxies for several Gyrs, and (3) once
begun, satellite star formation quenching occurs rapidly. These results place
strong constraints on satellite-specific quenching mechanisms, as we will
discuss further in companion papers.
