Recent star formation in local, morphologically disturbed spheroidal
  galaxies on the optical red sequence
  We combine GALEX (ultra-violet; UV) and SDSS (optical) photometry to study
the recent star formation histories of ~100 field galaxies on the optical red
sequence, a large fraction of which exhibit widespread signs of disturbed
morphologies in deep optical imaging that are consistent with recent merging
events. More than 70% of bulge-dominated galaxies in this sample show tidal
features at a surface brightness limit of 28 mag arcsec^-2. We find that, while
they inhabit the optical red sequence, they show a wide spread in their UV
colours (~4 mags), akin to what has been discovered recently in the general
early-type population. A strong correlation is found between UV colour and the
strength of the tidal distortions, such that the bluest galaxies are more
distorted. This strongly suggests that the blue UV colours seen in many nearby
early-types are driven by (low-level) merger-induced star formation within the
last 3 Gyrs, contributing less than 10% of the stellar mass. If the ongoing
mergers in this sample, which have a median mass ratio of 1:4, are
representative of the nearby red merger population, then less than 25% of the
new stellar mass in the remnants is typically added through merger-induced star
formation. While the dust extinction in the inter-stellar medium (ISM) in these
galaxies is small [E(B-V)<0.1], the local dust content of the star-forming
regions is, on average, a factor of 3 higher. Finally, we use our theoretical
machinery to provide a recipe for calculating the age of the most recent star
formation event (t2) in nearby (z<0.1) red early-type galaxies: Log (t2) [Gyrs]
~ 0.6.[(NUV-u)-(g-z)-1.73], where NUV, u, g and z are the observed photometric
magnitudes of the galaxies in the GALEX/SDSS filtersets.
