Kinematic Structure of the Large Magellanic Cloud Globular Cluster System from Gaia eDR3 and Hubble Space Telescope Proper Motions

TL;DR

This study uses Gaia eDR3 and Hubble data to analyze the 3D motions of 32 globular clusters in the Large Magellanic Cloud, revealing a disk-like rotation pattern and suggesting a common formation origin.

Contribution

First detailed 6D phase-space analysis of LMC globular clusters showing disk-like kinematics and a single formation mechanism, contrasting with the Milky Way.

Findings

Most clusters follow a flattened, rotating disk pattern.

Velocity dispersions are around 30 km/s, similar to LMC's stellar disk.

No significant accreted halo globular cluster population detected.

Abstract

We have determined bulk proper motions (PMs) for 31 LMC GCs from Gaia eDR3 and Hubble Space Telescope data using multiple independent analysis techniques. Combined with literature values for distances, line-of-sight velocities and existing bulk PMs, we extract full 6D phase-space information for 32 clusters, allowing us to examine the kinematics of the LMC GC system in detail. Except for two GCs (NGC 2159 and NGC 2210) for which high velocities suggest they are not long-term members of the LMC system, the data are consistent with a flattened configuration that rotates like the stellar disk. The one-dimensional velocity dispersions are of order 30 km/s, similar to that of old stellar populations in the LMC disk. Similar to the case for Milky Way disk clusters, the velocity anisotropy is such that the dispersion is smallest in the azimuthal direction; however, alternative anisotropies cannot be ruled out due to distance uncertainties. The data are consistent with a single multi-dimensional Gaussian velocity distribution. Given the non-collisional nature of the LMC disk, this suggests that most, if not all, of the LMC GCs are formed by a single formation mechanism in the stellar disk, despite a significant spread in age and metallicity. Any accreted halo GC population is absent or far smaller in the LMC compared to the Milky Way.