Decoding the Bifurcated Red Giant Branch as a Tracer of Multiple Stellar Populations in the Young Large Magellanic Cloud Cluster NGC 2173

Multiple stellar populations (MPs) representing star-to-star light-element abundance variations are common in nearly all ancient Galactic globular clusters (GCs). 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 GCs and young massive clusters might share a common formation process.