A likely runaway star cluster in the outer disc of the Large Magellanic Cloud

TL;DR

This study identifies a 0.9 Gyr old star cluster in the outer disc of the Large Magellanic Cloud, suggesting it was scattered from the inner regions, and provides insights into its origin and dynamics.

Contribution

It presents the discovery and detailed analysis of a star cluster in the LMC's outer disc, revealing its likely origin and dynamical history, which was not previously documented.

Findings

The cluster is approximately 0.9 Gyr old.

It likely originated from the inner LMC regions.

Its orbital velocity is about 60% higher than typical outer disc clusters.

Abstract

We present results from photometric and spectroscopic data obtained with SOAR and Gemini observatory facilities in the field of a recently discovered star cluster. The cluster, projected towards the Eastern side of the outer disc of the Large Magellanic Cloud (LMC), was originally placed nearly 10 kpc behind the LMC with an age and metallicity typical of the innermost LMC star cluster population. We assigned radial velocity (RV) memberships to stars observed spectroscopically, and derived the cluster age and distance from theoretical isochrone fitting to the cluster colour-magnitude diagram. The new object turned out to be a 0.9 Gyr old outer LMC disc cluster, which possibly reached the present position after being scattered from the innermost LMC regions where it might have been born. We arrived at this conclusion by examining the spatial distribution of LMC star clusters of similar age, by comparing the derived spectroscopic metallicity with that expected for an outside-in galaxy formation scenario, by considering the cluster internal dynamical stage as inferred from its derived structural parameters and by estimating the circular velocity of a disc that rotates with the corresponding star cluster radial velocity at the cluster's deprojected distance, which resulted to be nearly 60 per cent higher than that of most of the outer LMC disc clusters.