2019MNRAS.487.3693J

Gaia Data Release 2 provides a wealth of data to study the internal structure of nearby globular clusters (GCs). We use this data to investigate the internal kinematics of 10 nearby GCs, with a particular focus on their poorly studied outer regions. We apply a strict set of selection criteria to remove contaminating sources and create pure cluster-member samples over a significant fraction of the radial range of each cluster. We confirm previous measurements of rotation (or a lack thereof) in the inner regions of several clusters, while extending the detection of rotation well beyond where it was previously measured and finding a steady decrease in rotation with radius. We also determine the orbital anisotropy profile and determine that clusters have isotropic cores, are radially anisotropic out to ≃4 half-light radii or 35 per cent of their limiting radii, and are then isotropic out to the limits of our data sets. We detect for the first time the presence of radial anisotropy in M 22, while confirming previous detections of radial anisotropy in 47 Tuc, M 13, M 15, and ω Cen's innermost regions. The implications of these measurements are that clusters can be separated into two categories: (1) clusters with observed radial anisotropy that likely formed tidally underfilling or are dynamically young, and (2) clusters that are primarily isotropic that likely formed tidally filling or are dynamically old.