Formation of anomalous globular clusters with metallicity spreads: A unified picture

TL;DR

This paper proposes a unified model explaining the formation of anomalous globular clusters with internal metallicity spreads through the merging of GCs within dwarf galaxies, supported by numerical simulations and chemical evolution analysis.

Contribution

It introduces a new scenario where GC mergers in dwarf galaxies produce anomalous GCs with observed abundance spreads, linking their formation to galaxy disruption.

Findings

GC mergers in dwarf galaxies can produce metallicity spreads of 0.2 dex.

Merged GCs can capture field stars during spiral-in.

The model explains the chemical abundance patterns observed in anomalous GCs.

Abstract

Recent observations have revealed that at least 8 globular clusters (GCs) in the Galaxy show internal abundance spreads in [Fe/H]. We investigate the origin of these `anomalous' GCs using numerical simulations of GCs in the dwarfs orbiting around the Galaxy and chemical evolution model of dwarfs hosting the GCs. The principal results are as follows. GCs formed in a host dwarf galaxy with a total mass of ~ 10^10 M_sun can merge to form a single nuclear GC before the host is completely destroyed by the Galaxy, if they are massive (> 3*10^5 M_sun) and if they are formed in the inner region (R<400 pc). The GC merger remnants can capture field stars during its spiral-in to nuclear regions. If two GCs are formed from star formation events separated by ~300 Myr in their host dwarf, then the new GC formed from GC merging can have [Fe/H] spread of 0.2 dex and [Ba/Fe] spread of 0.3 dex. GCs formed from GC merging can show variety of internal abundance spreads depending on the details of their hosts' chemical evolution. We suggest that anomalous GCs were formed from GC merging that occurred before the destruction of GC host dwarfs yet after self-enrichment processes responsible for the observed anti-correlations between chemical abundances of light elements. We also suggest that the observed no/little dependence of [Eu/Fe] on [Fe/H] in the Galactic GC M22 is evidence of massive dwarf galaxies hosting these anomalous GCs.