NGC 4656UV: A UV-selected Tidal Dwarf Galaxy Candidate
  We report the discovery of a UV-bright tidal dwarf galaxy candidate in the
NGC 4631/4656 galaxy group, which we designate NGC 4656UV. Using survey and
archival data spanning from 1.4 GHz to the ultraviolet we investigate the gas
kinematics and stellar properties of this system. The HI morphologies of NGC
4656UV and its parent galaxy NGC 4656 are extremely disturbed, with significant
amounts of counterrotating and extraplanar gas. From UV-FIR photometry,
computed using a new method to correct for surface gradients on faint objects,
we find that NGC 4656UV has no significant dust opacity and a blue spectral
energy distribution. We compute a star formation rate of 0.027 M_sun yr^-1 from
the FUV flux and measure a total HI mass of 3.8x10^8 M_sun for the object.
Evolutionary synthesis modeling indicates that NGC 4656UV is a low metallicity
system whose only major burst of star formation occurred within the last
~260-290 Myr. The age of the stellar population is consistent with a rough
timescale for a recent tidal interaction between NGC 4656 and NGC 4631,
although we discuss the true nature of the object--whether it is tidal or
pre-existing in origin--in the context of its metallicity being a factor of ten
lower than its parent galaxy. We estimate that NGC 4656UV is either marginally
bound or unbound. If bound, it contains relatively low amounts of dark matter.
The abundance of archival data allows for a deeper investigation into this
dynamic system than is currently possible for most TDG candidates.
