# The orbital anisotropy profiles of nearby globular clusters from Gaia Data Release 2

## TL;DR

This study uses Gaia DR2 data to analyze the internal kinematics of 11 nearby globular clusters, revealing detailed rotation and anisotropy profiles, and classifying clusters based on their dynamical states.

## Contribution

It provides the first detection of radial anisotropy in M 22 and extends rotation measurements beyond previous limits, offering new insights into cluster formation and evolution.

## Key findings

- Clusters are isotropic at cores and outer regions, radially anisotropic at intermediate radii.
- Radial anisotropy detected in M 22, confirming previous findings in other clusters.
- Clusters can be categorized into dynamically young with radial anisotropy and old with isotropy.

## Abstract

Gaia Data Release 2 provides a wealth of data to study the internal structure of nearby globular clusters. We use this data to investigate the internal kinematics of 11 nearby globular clusters, 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 $\approx$ 4 half-light radii or $35\%$ of their limiting radii, and are then isotropic out to the limits of our datasets. 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 3, M 13, M 15, and $\omega$ 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 under-filling or are dynamically young, and 2) clusters that are primarily isotropic that likely formed tidally filling or are dynamically old.