We have explored GALEX UV properties of optical red sequence galaxies in 4 rich Abell clusters at z ? 0.1.
Inparticular we tried to find a hint of merger-induced recent star formation (RSF) in the red sequence galaxies. RSF fractions are calculated with various criteria for post-merger galaxies and normal red sequence galaxies based on their NUV - r’ colors. In this study it turned out that only 30% of the RSF red sequence galaxies involve tidally-disturbed features in cluster environment. It is possible that we are missing minor merger features with the deep optical images from the less massive regime (-21 < Mr' < -20) of our volume-limited sample. However, considering the timescale difference for the fading out of morphological merger features (~ 4 Gyr) and young stellar populations (~ 1 Gyr), the fraction of RSF red sequence galaxies without disturbed features is still significantly large. We also confirmed that those featureless RSF galaxies are mostly bulge-dominated. This result may imply that gas accretion in early-type galaxies plays a significant role in residual star formation of the early-type galaxies.