The AIMSS Project II: Dynamical-to-Stellar Mass Ratios Across the Star
  Cluster - Galaxy Divide
  The previously clear division between small galaxies and massive star
clusters is now occupied by objects called ultra compact dwarfs (UCDs) and
compact ellipticals (cEs). Here we combine a sample of UCDs and cEs with
velocity dispersions from the AIMSS project with literature data to explore
their dynamical-to-stellar mass ratios.
  We confirm that the mass ratios of many UCDs in the stellar mass range 10$^6$
-- 10$^9$ M$_{\odot}$ are systematically higher than those for globular
clusters which have mass ratios near unity. However, at the very highest masses
in our sample, i.e. 10$^9$ -- 10$^{10}$ M$_{\odot}$, we find that cE galaxies
also have mass ratios of close to unity, indicating their central regions are
mostly composed of stars.
  Suggested explanations for the elevated mass ratios of UCDs have included a
variable IMF, a central black hole, and the presence of dark matter. Here we
present another possible explanation, i.e. tidal stripping. Under various
assumptions, we find that the apparent variation in the mass ratio with stellar
mass and stellar density can be qualitatively reproduced by published tidal
stripping simulations of a dwarf elliptical galaxy. In the early stages of the
stripping process the galaxy is unlikely to be in virial equilibrium. At late
stages, the final remnant resembles the properties of $\sim$10$^7$ M$_{\odot}$
UCDs. Finally, we discuss the need for more detailed realistic modelling of
tidal stripping over a wider range of parameter space, and observations to
further test the stripping hypothesis.
