A genuine Large Magellanic Cloud age gap star cluster

TL;DR

This paper confirms the existence of a second star cluster in the Large Magellanic Cloud within the age gap, providing detailed age and metallicity measurements and discussing possible formation scenarios.

Contribution

It reports the discovery and characterization of a second LMC star cluster in the age gap, using deep imaging and star-by-star membership analysis.

Findings

KMHK 1592 has an age of 8.0+-0.5 Gyr and metallicity [Fe/H]=-1.0+-0.2 dex.

The cluster was identified using deep GEMINI GMOS images and is confirmed to be in the LMC.

Three formation scenarios are discussed: in-situ formation, capture, or accretion.

Abstract

We confirm the existence of a second Large Magellanic Cloud (LMC) star cluster, KMHK 1592, with an age that falls in the middle of the so-called LMC star cluster age gap, a long period of time (~ 4 - 11 Gyr) where no star cluster had been uncovered, except ESO121-SC03. The age (8.0+-0.5 Gyr) and the metallicity ([Fe/H]=-1.0+-0.2 dex) of KMHK1592 were derived from the fit of theoretical isochrones to the intrinsic star cluster colour-magnitude diagram sequences, which were unveiled using a robust star-by-star membership probability procedure. Because of the relative low brightness of the star cluster, deep GEMINI GMOS images were used. We discuss the pros and cons of three glimpsed scenarios that could explain the presence of both LMC age gap star clusters in the outskirts of the LMC, namely: in-situ star cluster formation, capture from the Small Magellanic Cloud, or accretion of a small dwarf galaxy.