Decoding the bifurcated red-giant branch as a tracer of multiple stellar populations in the young Large Magellanic Cloud cluster NGC 2173

TL;DR

This study provides the strongest evidence that the 1.7 Gyr-old Large Magellanic Cloud cluster NGC 2173 exhibits multiple stellar populations, indicating a shared formation process with ancient globular clusters.

Contribution

It is the first confirmation of multiple populations in a young (~1.7 Gyr) cluster, expanding understanding of cluster formation and evolution.

Findings

Bifurcation at the tip of the red-giant branch observed in HST images

Bimodality in red-giant-branch color distribution confirmed

NGC 2173 is the youngest cluster with confirmed multiple populations

Abstract

Multiple stellar populations (MPs) representing star-to-star light-element abundance variations are common in nearly all ancient Galactic globular clusters. Here we provide the strongest evidence yet that the populous, ~ 1.7 Gyr-old Large Magellanic Cloud cluster NGC 2173 also exhibits light-element abundance variations. Thus, our results suggest that NGC 2173 is the youngest cluster for which MPs have been confirmed to date. Our conclusion is based on the distinct bifurcation at the tip of its red-giant branch in high-quality color--magnitude diagrams generated from Hubble Space Telescope imaging observations. Our results are further supported by a detailed analysis of 'pseudo-$UBI$' maps, which reveal clear evidence of a bimodality in the cluster's red-giant-branch color distribution. Young clusters in the Magellanic Clouds can provide critical insights into galaxy evolution histories. Our discovery of MPs in NGC 2173 suggests that ancient Galactic globular clusters and young massive clusters might share a common formation process.