Internal kinematics of 9 globular clusters with HST

Here, we focus on internal kinematics of nine GGCs, obtained from space-based imaging over time baselines of >9yr. We exploit multiple avenues to assess the dynamical state of the target GGCs, constructing radial profiles of projected stellar density, proper motion dispersion, and anisotropy.

We posit that two-thirds (6/9) of our target GGCs are in an advanced dynamical state, and are close to (or have recently undergone) core-collapse, supported by at least two lines of evidence. First, we find relatively steep proper motion dispersion profiles, in accord with literature values for core-collapsed GGCs. Second, we find that our sample is, in the mean, isotropic even out to their half-light radii, although one of our target clusters (NGC6380) is tangentially anisotropic at >1{sigma} beyond its half-light radius, in accord with theoretical predictions for clusters evolving in strong tidal fields.