Dark Matter in Ultra-Diffuse Galaxies in the Virgo Cluster from their
  Globular Cluster Populations
  We present Keck/DEIMOS spectroscopy of globular clusters (GCs) around the
ultra-diffuse galaxies (UDGs) VLSB-B, VLSB-D, and VCC615 located in the central
regions of the Virgo cluster. We spectroscopically identify 4, 12, and 7 GC
satellites of these UDGs, respectively. We find that the three UDGs have
systemic velocities ($V_{sys}$) consistent with being in the Virgo cluster, and
that they span a wide range of velocity dispersions, from $\sim 16$ to $\sim
47$ km/s, and high dynamical mass-to-light ratios within the radius that
contains half the number of GCs ($ 407^{+916}_{-407}$, $21^{+15}_{-11}$,
$60^{+65}_{-38}$, respectively). VLSB-D shows possible evidence for rotation
along the stellar major axis and its $V_{sys}$ is consistent with that of the
massive galaxy M84 and the center of the Virgo cluster itself. These findings,
in addition to having a dynamically and spatially ($\sim 1$ kpc) off-centered
nucleus and being extremely elongated, suggest that VLSB-D could be tidally
perturbed. On the contrary, VLSB-B and VCC615 show no signals of tidal
deformation. Whereas the dynamics of VLSB-D suggest that it has a less massive
dark matter halo than expected for its stellar mass, VLSB-B and VCC615 are
consistent with a $\sim 10^{12}$ M$_{\odot}$ dark matter halo. Although our
samples of galaxies and GCs are small, these results suggest that UDGs may be a
diverse population, with their low surface brightnesses being the result of
very early formation, tidal disruption, or a combination of the two.
