Enrichment by supernovae in globular clusters with multiple populations

TL;DR

This paper investigates the chemical enrichment in globular clusters, especially omega Centauri, suggesting they are remnants of larger dwarf galaxies enriched by supernovae, with new calcium abundance data supporting this view.

Contribution

It provides calcium abundance measurements for seven globular clusters and argues these clusters are likely remnants of larger dwarf galaxies enriched by supernovae.

Findings

Calcium and heavy elements in clusters indicate supernova enrichment.

Current clusters' gravitational potentials can't retain supernova ejecta.

Clusters are probably remnants of disrupted dwarf galaxies.

Abstract

The most massive globular cluster in the Milky Way, omega Centauri, is thought to be the remaining core of a disrupted dwarf galaxy, as expected within the model of hierarchical merging. It contains several stellar populations having different heavy elemental abundances supplied by supernovae -- a process known as metal enrichment. Although M22 appears to be similar to omega Cen, other peculiar globular clusters do not. Therefore omega Cen and M22 are viewed as exceptional, and the presence of chemical inhomogeneities in other clusters is seen as `pollution' from the intermediate-mass asymptotic-giant-branch stars expected in normal globular clusters. Here we report Ca abundances for seven globular clusters and compare them to omega Cen. Calcium and other heavy elements can only be supplied through numerous supernovae explosions of massive stars in these stellar systems, but the gravitational potentials of the present-day clusters cannot preserve most of the ejecta from such explosions. We conclude that these globular clusters, like omega Cen, are most probably the relics of more massive primeval dwarf galaxies that merged and disrupted to form the proto-Galaxy.