Multiple Populations in Integrated Light Spectroscopy of Intermediate Age Clusters

Abstract

The presence of star-to-star light-element abundance variations (a.k.a. multiple populations, MPs) appears to be ubiquitous within old and massive clusters in the Milky Way and all studied nearby galaxies. Most previous studies have focussed on resolved images or spectroscopy of individual stars, although there has been significant effort in the past few years to look for multiple population signatures in integrated light spectroscopy. If proven feasible, integrated light studies offer a potential way to vastly open parameter space, as clusters out to tens of Mpc can be studied. We use the NaD lines in the integrated spectra of two clusters with similar ages ($2-3$ Gyr) but very different masses, NGC 1978 ($\sim 3\times 10^5$ Msun) in the LMC and G114 ($1.7\times 10^7$ Msun) in NGC 1316. For NGC 1978, our findings agree with resolved studies of individual stars which did not find evidence for Na spreads. However, for G114, we find clear evidence for the presence of multiple populations. The fact that the same anomalous abundance patterns are found in both the intermediate age and ancient GCs lends further support to the notion that young massive clusters are effectively the same as the ancient globular clusters, only separated in age.

MNRAS letters, in press (5 pages + appendix)

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• Integrated photometry of multiple stellar populations in Globular Clusters
• An outer shade of Pal: Abundance analysis of the outer halo globular cluster Palomar 13
• Leveraging HST with MUSE: II. Na-abundance variations in intermediate age star clusters
• Searching for Multiple Populations in the Integrated Light of the Young and Extremely Massive Clusters in the Merger Remnant NGC~7252
• Detailed Chemical Abundances of Star Clusters in the Large Magellanic Cloud