The environmental dependence of rapidly quenching and rejuvenating galaxies

Abstract

ABSTRACT By combining H α flux measurements from the Sloan Digital Sky Survey (SDSS) with ultraviolet (UV) flux observations from the Galaxy Evolution Explorer (GALEX), we examine the environmental dependence (through central/satellite distinction) of the rapid quenching and rejuvenation of galaxies. H α emissions trace the most massive stars, thereby indicating star formation on time-scales of ∼10 Myr, while UV emission traces star formation on time-scales of ∼100 Myr. These varying time-scales are exploited to probe the most recent star formation histories of galaxies. In this work, we define a class of transient galaxies that have UV emission typical of star formation but negligible H α emission. We find that the occurrence of these transients has a strong stellar mass dependence in both the satellite and central populations. However, while at stellar masses greater than M* ∼ 1010 M⊙ they occur with equal frequency regardless of environmental class, at lower stellar masses they are more common in satellites only, with an excess of about 1 percentage point across all low stellar mass galaxies. These satellite transients also have a strong halo mass and group-centric radial dependence suggesting they are driven by an environmental process. Finally, we select a sample of galaxies with H α emission but not UV emission that could contain short time-scale rejuvenating galaxies. These rejuvenating candidates are few in number and do not have a strong difference in their occurrence rate in centrals or satellites. These unique probes point to an environmental quenching mechanism that occurs on short time-scales after the satellite has been in the group environment for a significant time – consistent with ‘delayed-then-rapid’ quenching.