# The eye of Gaia on globular clusters kinematics: internal rotation

## TL;DR

This study uses Gaia data to measure three-dimensional velocities in 62 globular clusters, revealing rotation in 15 clusters and suggesting a primordial origin for their systemic rotation.

## Contribution

It provides the first comprehensive analysis of internal rotation in a large sample of globular clusters using Gaia proper motions and line-of-sight velocities.

## Key findings

- Rotation detected in 15 clusters with significant amplitude.
- Weak correlation between rotation strength and cluster properties.
- No significant alignment of rotation axes with orbital poles.

## Abstract

We derived the three-dimensional velocities of individual stars in a sample of 62 Galactic globular clusters using proper motions from the second data release of the Gaia mission together with the most comprehensive set of line-of-sight velocities with the aim of investigating the rotation pattern of these stellar systems. We detect the unambiguous signal of rotation in 15 clusters at amplitudes which are well above the level of random and systematic errors. For these clusters, we derived the position and inclination angle of the rotation axis with respect to the line of sight and the overall contribution of rotation to the total kinetic energy budget. The rotation strengths are weakly correlated with the half-mass radius, the relaxation time and anticorrelated with the destruction rate, while no significant alignment of the rotation axes with the orbital poles has been observed. This evidence points toward a primordial origin of the systemic rotation in these stellar systems.