Extended Light in E/S0 Galaxies and Implications for Disk Rebirth
  The recent discovery of extended ultraviolet (XUV) disks around a large
fraction of late-type galaxies provides evidence for unexpectedly large-scale
disk building at recent epochs. Combining GALEX UV observations with deep
optical and Spitzer IR imaging, we search for XUV disks in a sample of nearby
low-to-intermediate mass E/S0 galaxies to explore evidence for disk rebuilding
after mergers. Preliminary visual classification yields ten XUV-disk candidates
from the full sample of 30, intriguingly similar to the ~30% frequency for
late-type galaxies. These XUV candidates occur at a wide range of masses and on
both the red and blue sequences in color vs. stellar mass, indicating a
possible association with processes like gas accretion and/or galaxy
interactions that would affect the galaxy population broadly. We go on to apply
the quantitative Type 1 and Type 2 XUV-disk definitions to a nine-galaxy
subsample analyzed in detail. For this subsample, six of the nine are Type 1
XUVs, i.e., galaxies with UV structure beyond the expected star formation
threshold. The other three come close to satisfying the Type 2 definition, but
that definition proves problematic to apply to this sample: the NUV-derived
star formation threshold radii for our E/S0s often lie inside the 80% Ks-band
light (K80) radii, violating an implicit assumption of the Type 2 definition,
or lie outside but not as far as the definition requires. Nonetheless, the
three otherwise Type 2-like galaxies ("modified Type 2 XUVs") have higher star
formation rates and bluer FUV - NUV colors than the Type 1 XUVs in the sample.
We propose that Type 1 XUVs may reflect early or inefficient stages of star
formation, while modified Type 2 XUVs perhaps reflect inside-out disk regrowth.
