Gaia EDR3 view on Galactic globular clusters

TL;DR

This paper utilizes Gaia EDR3 data to analyze the kinematic properties of 170 Milky Way globular clusters, revealing rotation, anisotropy, and systematic uncertainties in measurements, thereby enhancing understanding of cluster dynamics.

Contribution

It provides the first comprehensive kinematic analysis of a large sample of globular clusters using Gaia EDR3, including rotation signatures and error assessments.

Findings

Detected rotation in over 20 clusters.

Identified systematic uncertainties in Gaia EDR3 data.

Suggested Gaia parallaxes are slightly overestimated.

Abstract

We use the data from Gaia Early Data Release 3 (EDR3) to study the kinematic properties of Milky Way globular clusters. We measure the mean parallaxes and proper motions (PM) for 170 clusters, determine the PM dispersion profiles for more than 100 clusters, uncover rotation signatures in more than 20 objects, and find evidence for radial or tangential PM anisotropy in a dozen richest clusters. At the same time, we use the selection of cluster members to explore the reliability and limitations of the Gaia catalogue itself. We find that the formal uncertainties on parallax and PM are underestimated by 10-20% in dense central regions even for stars that pass numerous quality filters. We explore the the spatial covariance function of systematic errors, and determine a lower limit on the uncertainty of average parallaxes and PM at the level 0.01 mas and 0.025 mas/yr, respectively. Finally, a comparison of mean parallaxes of clusters with distances from various literature sources suggests that the parallaxes (after applying the zero-point correction suggested by Lindegren et al. 2021) are overestimated by 0.01+-0.003 mas. Despite these caveats, the quality of Gaia astrometry has been significantly improved in EDR3 and provides valuable insights into the properties of star clusters.