Fresh Insights on the Kinematics of M49's Globular Cluster System with
  MMT/Hectospec Spectroscopy
  We present the first results of an MMT/Hectospec campaign to measure the
kinematics of globular clusters (GCs) around M49 -- the brightest galaxy in the
Virgo galaxy cluster, which dominates the Virgo B subcluster. The data include
kinematic tracers beyond 95 kpc (~5.2 effective radii) for M49 for the first
time, enabling us to achieve three key insights reported here. First, beyond
~20'-30' (~100-150 kpc), the GC kinematics sampled along the minor photometric
axis of M49 become increasingly hotter, indicating a transition from GCs
related to M49 to those representing the Virgo B intra-cluster medium. Second,
there is an anomaly in the line-of-sight radial velocity dispersion
($\sigma_{r,los}$) profile in an annulus ~10-15' (~50-90 kpc) from M49 in which
the kinematics cool by $\Delta \sigma_{r,los}~150$ km s$^{-1}$ relative to
those in- or outward. The kinematic fingerprint of a previous accretion event
is hinted at in projected phase-space, and we isolate GCs that both give rise
to this feature, and are spatially co-located with two prominent stellar shells
in the halo of M49. Third, we find a subsample of GCs with velocities
representative of the dwarf galaxy VCC1249 that is currently interacting with
M49. The spatial distribution of these GCs closely resembles the morphology of
VCC1249's isophotes, indicating that several of these GCs are likely in the act
of being stripped from the dwarf during its passage through M49's halo. Taken
together, these results point toward the opportunity of witnessing on-going
giant halo assembly in the depths of a cluster environment.
