# Using Gaia for studying Milky Way star clusters

## TL;DR

This paper leverages Gaia Data Release 2 to analyze the dynamics of Milky Way globular clusters, measuring their proper motions, internal rotation, and velocity dispersions to better understand the galaxy's gravitational potential.

## Contribution

It presents a novel analysis combining Gaia data with dynamical models to simultaneously determine the Milky Way potential and globular cluster properties.

## Key findings

- Precise proper motions measured for all globular clusters
- Detected rotation in 10 clusters with Gaia data
- Velocity dispersion profiles agree with previous measurements

## Abstract

We review the implications of the Gaia Data Release 2 catalogue for studying the dynamics of Milky Way globular clusters, focusing on two separate topics. The first one is the analysis of the full 6-dimensional phase-space distribution of the entire population of Milky Way globular clusters: their mean proper motions (PM) can be measured with an exquisite precision (down to 0.05 mas/yr, including systematic errors). Using these data, and a suitable ansatz for the steady-state distribution function (DF) of the cluster population, we then determine simultaneously the best-fit parameters of this DF and the total Milky Way potential. We also discuss possible correlated structures in the space of integrals of motion. The second topic addresses the internal dynamics of a few dozen of the closest and richest globular clusters, again using the Gaia PM to measure the velocity dispersion and internal rotation, with a proper treatment of spatially correlated systematic errors. Clear rotation signatures are detected in 10 clusters, and a few more show weaker signatures at a level >=0.05$ mas/yr. PM dispersion profiles can be reliably measured down to 0.1 mas/yr, and agree well with the line-of-sight velocity dispersion profiles from the literature.