NUV signatures of environment driven galaxy quenching in SDSS groups
  We have investigated the effect of group environment on residual star
formation in galaxies, using Galex NUV galaxy photometry with the SDSS group
catalogue of Yang et al. (2007). We compared the (NUV $- r$) colours of grouped
and non-grouped galaxies, and find a significant increase in the fraction of
red sequence galaxies with blue (NUV $- r$) colours outside of groups. When
comparing galaxies in mass matched samples of satellite (non-central), and
non-grouped galaxies, we found a > 4{\sigma} difference in the distribution of
(NUV $- r$) colours, and an (NUV $- r$) blue fraction $> 3{\sigma}$ higher
outside groups. A comparison of satellite and non-grouped samples has found the
NUV fraction is a factor of $\sim2$ lower for satellite galaxies between
$10^{10.5}M_{\bigodot}$ and $10^{10.7}M_{\bigodot}$, showing that higher mass
galaxies are more able to form stars when not influenced by a group potential.
There was a higher (NUV $- r$) blue fraction of galaxies with lower Sersic
indices (n < 3) outside of groups, not seen in the satellite sample. We have
used stellar population models of Bruzual & Charlot (2003) with multiple burst,
or exponentially declining star formation histories to find that many of the
(NUV $- r$) blue non-grouped galaxies can be explained by a slow ($\sim 2$ Gyr)
decay of star formation, compared to the satellite galaxies. We suggest that
taken together, the difference in (NUV $- r$) colours between samples can be
explained by a population of secularly evolving, non-grouped galaxies, where
star formation declines slowly. This slow channel is less prevalent in group
environments where more rapid quenching can occur.
