The environmental dependence of rapidly-quenching and rejuvenating
  galaxies
  By combining H$\alpha$ flux measurements from the Sloan Digital Sky Survey
(SDSS) with 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$\alpha$ emissions trace the
most massive stars, thereby indicating star-formation on timescales of $\sim
10$ Myr, while UV emission traces star-formation on timescales of $\sim 100$
Myr. These varying timescales are exploited to probe the most recent
star-formation histories of galaxies. In this work, we define a class of
transient galaxies which have UV emission typical of star-formation but
negligible H$\alpha$ emission. We find that the occurrence of these transients
has a strong stellar mass dependence in both the satellite and central
population. However, while at stellar masses greater than $\sim 10^{10}
M_\odot$ 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$\alpha$ emission but not UV emission which could
contain short-timescale 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 which occurs on short timescales after the satellite has
been in the group environment for a significant time - consistent with
'delayed-then-rapid' quenching.
