Self-Enriched Globular Clusters and the History of the Milky Way

Globular clusters (GCs) can provide excellent tracers of the accretion history of a galaxy. The mean metallicity of a GC can be easily measured, Gaia proper motions allow the determination of 3D kinematics, and a significant fraction of Milky Way GCs also have precise age estimates. GCs that come from the same protogalactic progenitor ought to track out specific tracks in age-metallicity space and lie in contiguous regions of kinematic phase space. These techniques have allowed the discovery of important accretion events such as Gaia-Enceladus, Kraken, and others.

However, this technique assumes that the metallicity we see today is representative of the metallicity of the gas from which the GC formed. Self-enrichment within GCs can significantly affect the metallicities of the stars we see today, particularly for massive and metal-poor GCs. We use self-enrichment models to correct for this and re-examine the age-metallicity-kinematic structure of the Milky Way’s GC population. We find that accounting for self-enrichment in GCs does not change the overall picture of the history of the Milky Way, but does call into question which protogalactic progenitor some individual GCs ought to be assigned to.