The Dynamical Evolution of Accreted Star Clusters in the Milky Way

Abstract

We perform $N$-body simulations of star clusters in time-dependant galactic potentials. Since the Milky Way was built-up through mergers with dwarf galaxies, its globular cluster population is made up of clusters formed both during the initial collapse of the Galaxy and in dwarf galaxies that were later accreted. Throughout a dwarf-Milky Way merger, dwarf galaxy clusters are subject to a changing galactic potential. Building on our previous work, we investigate how this changing galactic potential affects the evolution of a cluster's half mass radius. In particular, we simulate clusters on circular orbits around a dwarf galaxy that either falls into the Milky Way or evaporates as it orbits the Milky Way. We find that the dynamical evolution of a star cluster is determined by whichever galaxy has the strongest tidal field at the position of the cluster. Thus, clusters entering the Milky Way undergo changes in size as the Milky Way tidal field becomes stronger and that of the dwarf diminishes. We find that ultimately accreted clusters quickly become the same size as a cluster born in the Milky Way on the same orbit. Assuming their initial sizes are similar, clusters born in the Galaxy and those that are accreted cannot be separated based on their current size alone.

9 pages, 4 figures, accepted for publication in MNRAS

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• Characterization of the velocity anisotropy of accreted globular clusters
• The VISCACHA survey -- II. Structure of star clusters in the Magellanic Clouds periphery
• Kinematic fingerprint of core-collapsed globular clusters
• Enlightening the dynamical evolution of Galactic open clusters: an approach using Gaia DR3 and analytical descriptions
• The Early Evolution of Star Clusters in Compressive and Extensive Tidal Fields
• Globular Cluster Scale Sizes in Giant Galaxies: Orbital Anisotropy and Tidally Under-filling Clusters in M87, NGC 1399, and NGC 5128
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• Tidal stripping as a mechanism for placing globular clusters on wide orbits: the case of MGC1 in M31