Kinematics of dwarf galaxies in gas-rich groups, and the survival and
  detectability of tidal dwarf galaxies
  We present DEIMOS multi-object spectroscopy (MOS) of 22 star-forming dwarf
galaxies located in four gas-rich groups, including six newly-discovered
dwarfs. Two of the galaxies are strong tidal dwarf galaxy (TDG) candidates
based on our luminosity-metallicity relation definition. We model the rotation
curves of these galaxies. Our sample shows low mass-to-light ratios
(M/L=0.73$\pm0.39M_\odot/L_\odot$) as expected for young, star-forming dwarfs.
One of the galaxies in our sample has an apparently strongly-falling rotation
curve, reaching zero rotational velocity outside the turnover radius of
$r_{turn}=1.2r_e$. This may be 1) a polar ring galaxy, with a tilted bar within
a face-on disk; 2) a kinematic warp. These scenarios are indistinguishable with
our current data due to limitations of slit alignment inherent to MOS-mode
observations. We consider whether TDGs can be detected based on their tidal
radius, beyond which tidal stripping removes kinematic tracers such as
H$\alpha$ emission. When the tidal radius is less than about twice the turnover
radius, the expected falling rotation curve cannot be reliably measured. This
is problematic for as much as half of our sample, and indeed more generally,
galaxies in groups like these. Further to this, the H$\alpha$ light that
remains must be sufficiently bright to be detected; this is only the case for
three (14%) galaxies in our sample. We conclude that the falling rotation
curves expected of tidal dwarf galaxies are intrinsically difficult to detect.
