Recent galaxy mergers and residual star formation of red sequence
  galaxies in galaxy clusters
  This study explored the GALEX ultraviolet (UV) properties of optical red
sequence galaxies in 4 rich Abell clusters at z \leq 0.1. In particular, we
tried to find a hint of merger-induced recent star formation (RSF) in red
sequence galaxies. Using the NUV - r' colors of the galaxies, RSF fractions
were derived based on various criteria for post-merger galaxies and normal
galaxies. Following k-correction, about 36% of the post-merger galaxies were
classified as RSF galaxies with a conservative criterion (NUV - r' \leq 5), and
that number was doubled (~ 72%) when using a generous criterion (NUV - r' \leq
5.4). The trend was the same when we restricted the sample to galaxies within
0.5xR_{200}. Post-merger galaxies with strong UV emission showed more violent,
asymmetric features in the deep optical images. The RSF fractions did not show
any trend along the clustocentric distance within R_{200}. We performed a
Dressler-Shectman test to check whether the RSF galaxies had any correlation
with the sub-structures in the galaxy clusters. Within R_{200} of each cluster,
the RSF galaxies did not appear to be preferentially related to the clusters'
sub-structures. Our results suggested that only 30% of RSF red sequence
galaxies show morphological hints of recent galaxy mergers. This implies that
internal processes (e.g., stellar mass-loss or hot gas cooling) for the supply
of cold gas to early-type galaxies may play a significant role in the residual
star formation of early-type galaxies at a recent epoch.
