Shocked POststarburst Galaxy Survey. III. The Ultraviolet Properties of
  SPOGs
  The Shocked POststarburst Galaxy Survey (SPOGS) aims to identify galaxies in
the transitional phase between actively star-forming and quiescence with
nebular lines that are excited from shocks rather than star formation
processes. We explored the ultraviolet (UV) properties of objects with
near-ultraviolet (NUV) and far-ultraviolet (FUV) photometry from archival GALEX
data; 444 objects were detected in both bands, 365 in only NUV, and 24 in only
FUV, for a total of 833 observed objects. We compared SPOGs to samples of
Star-forming galaxies (SFs), Quiescent galaxies (Qs), classical E+A
post-starburst galaxies, active galactic nuclei (AGN) host galaxies, and
interacting galaxies. We found that SPOGs have a larger range in their FUV-NUV
and NUV-r colors compared to most of the other samples, although all of our
comparison samples occupied color space inside of the SPOGs region. Based on
their UV colors, SPOGs are a heterogeneous group, possibly made up of a mixture
of SFs, Qs, and/or AGN. Using Gaussian mixture models, we are able to recreate
the distribution of FUV-NUV colors of SPOGs and E+A galaxies with different
combinations of SFs, Qs, and AGN. We find that the UV colors of SPOGs require a
>60% contribution from SFs, with either Qs or AGN representing the remaining
contribution, while UV colors of E+A galaxies required a significantly lower
fraction of SFs, supporting the idea that SPOGs are at an earlier point in
their transition from quiescent to star-forming than E+A galaxies.
