A Search for Young Stars in the S0 Galaxies of a Super-Group at z=0.37
  We analyze GALEX UV data for a system of four gravitationally-bound groups at
z=0.37, SG1120, which is destined to merge into a Coma-mass cluster by z=0, to
study how galaxy properties may change during cluster assembly. Of the 38
visually-classified S0 galaxies, with masses ranging from log(M_*)~10-11, we
detect only one in the NUV channel, a strongly star-forming S0 that is the
brightest UV source with a measured redshift placing it in SG1120. Stacking the
undetected S0 galaxies (which generally lie on or near the optical red-sequence
of SG1120) still results in no NUV/FUV detection (<2 sigma). Using our limit in
the NUV band, we conclude that for a rapidly truncating star formation rate,
star formation ceased *at least* ~0.1 to 0.7 Gyr ago, depending on the strength
of the starburst prior to truncation. With an exponentially declining
star-formation history over a range of time-scales, we rule out recent
star-formation over a wide range of ages. We conclude that if S0 formation
involves significant star formation, it occurred well before the groups were in
this current pre-assembly phase. As such, it seems that S0 formation is even
more likely to be predominantly occurring outside of the cluster environment.
