An Extragalactic Chromosome Map: The intermediate age SMC Cluster Lindsay 1

TL;DR

This study uses HST UV photometry to compare the multiple populations phenomenon in the 7.5 Gyr SMC cluster Lindsay 1 with Galactic globular clusters, revealing similar properties across different ages and galaxies.

Contribution

It provides the first direct comparison of MPs in an intermediate-age cluster and Galactic GCs using consistent UV photometry, confirming the universality of MPs.

Findings

Lindsay 1 shows MPs similar to those in Galactic GCs.

The MPs phenomenon is consistent across different ages and host galaxies.

UV photometry effectively reveals MPs in extragalactic clusters.

Abstract

The discovery of star-to-star abundance variations (a.k.a. multiple populations - MPs) within globular clusters (GCs), which are generally not found in the field or in lower mass open clusters, has led to a search for the unique property of GCs that allow them to host this phenomenon. Recent studies have shown that MPs are not limited to the ancient GCs but are also found in massive clusters with ages down to (at least) 2 Gyr. This finding is important for understanding the physics of the MP phenomenon, as these young clusters can provide much stronger constraints (e.g. on potential age spreads within the clusters) than older ones. However, a direct comparison between ancient GCs and intermediate clusters has not yet been possible due to the different filters adopted in their studies. Here we present new HST UV photometry of the 7.5 Gyr, massive SMC cluster, Lindsay 1, in order to compare its pseudo colour-colour diagram to that of Galactic GCs. We find that they are almost identical and conclude that the MPs phenomenon is the same, regardless of cluster age and host galaxy.