Globular cluster formation efficiencies from black-hole X-ray binary feedback

TL;DR

This paper explores how feedback from black-hole X-ray binaries in young star clusters can influence globular cluster formation efficiency and metallicity distribution, offering a new perspective on their origin.

Contribution

It introduces a simple toy model showing BHXB feedback can enhance globular cluster formation efficiency and explain metallicity bimodality without requiring bimodal field-star metallicity.

Findings

BHXB feedback can reduce gas in young clusters before supernovae occur.

Lower metallicity increases BHXB formation, leading to higher GC efficiency.

The model reproduces observed GC metallicity bimodality in some galaxies.

Abstract

We investigate a scenario in which feedback from black-hole X-ray binaries (BHXBs) sometimes begins inside young star clusters before strong supernova feedback. Those BHXBs could reduce the gas fraction inside embedded young clusters whilst maintaining virial equilibrium, which may help globular clusters (GCs) to stay bound when supernova-driven gas ejection subsequently occurs. Adopting a simple toy model with parameters guided by BHXB population models, we produce GC formation efficiencies consistent with empirically-inferred values. The metallicity dependence of BHXB formation could naturally explain why GC formation efficiency is higher at lower metallicity. For reasonable assumptions about that metallicity dependence, our toy model can produce a GC metallicity bimodality in some galaxies without a bimodality in the field-star metallicity distribution.