Globular Cluster Abundances and What They Can Tell Us About Galaxy Formation

TL;DR

This review discusses how globular cluster chemical properties inform us about the Milky Way's formation, highlighting evidence from abundance ratios, multiple populations, and their potential origins as galaxy nuclei or accreted systems.

Contribution

It synthesizes current knowledge on globular cluster abundances and their implications for galaxy formation, including new insights into their multiple populations and origins.

Findings

Globular clusters have chemical similarities with halo field stars.

Some GCs show evidence of multiple stellar populations with different enrichment histories.

Potential identification of additional GCs with complex populations, like NGC 2419.

Abstract

We review the properties of globular clusters which make them useful for studying the Galactic halo, Galactic chemical evolution, and the early stages of the formation of the Milky Way. We review the evidence that GCs have a chemical inventory similar to those of halo field stars. We discuss the abundance ratios for dSph galaxies and show that it is possible to have formed at least part the Galactic halo field stellar population by dissolving globular clusters and/or accreting dSph galaxies but only if this occurred at an early stage in the formation of the Galaxy. We review the constraints on halo formation timescales deduced from the low Mg isotopic ratios in metal-poor halo field dwarfs which indicate that AGB stars did not have time to contribute significantly, while M71 contains two populations, one without and also one with a substantial AGB contribution. We review the limited evidence for GCs with a second population showing additional contributions from SNII, currently confined to Omega Cen, M54, and M22, all of which may have been the nuclei or central regions of accreted galaxies. We check our own data for additional such GCs, and find preliminary indications that NGC 2419, a massive GC far in the outer Galactic halo, may also belong to this group.