The dynamics of the globular cluster NGC3201 out to the Jacobi radius
  As part of a chemo-dynamical survey of five nearby globular clusters with
2dF/AAOmega on the AAT, we have obtained kinematic information for the globular
cluster NGC3201. Our new observations confirm the presence of a significant
velocity gradient across the cluster which can almost entirely be explained by
the high proper motion of the cluster. After subtracting the contribution of
this perspective rotation, we found a remaining rotation signal with an
amplitude of $\sim1\ km/s$ around a different axis to what we expect from the
tidal tails and the potential escapers, suggesting that this rotation is
internal and can be a remnant of its formation process. At the outer part, we
found a rotational signal that is likely a result from potential escapers. The
proper motion dispersion at large radii reported by Bianchini et al. has
previously been attributed to dark matter. Here we show that the LOS dispersion
between 0.5-1 Jacobi radius is lower, yet above the predictions from an N-body
model of NGC3201 that we ran for this study. Based on the simulation, we find
that potential escapers cannot fully explain the observed velocity dispersion.
We also estimate the effect on the velocity dispersion of different amounts of
stellar-mass black holes and unbound stars from the tidal tails with varying
escape rates and find that these effects cannot explain the difference between
the LOS dispersion and the N-body model. Given the recent discovery of tidal
tail stars at large distances from the cluster, a dark matter halo is an
unlikely explanation. We show that the effect of binary stars, which is not
included in the N-body model, is important and can explain part of the
difference in dispersion. We speculate that the remaining difference must be
the result of effects not included in the N-body model, such as initial cluster
rotation, velocity anisotropy and Galactic substructure.
