Globular Cluster Formation and Evolution in the Context of Cosmological Galaxy Assembly: Open Questions

TL;DR

This paper reviews key open questions about globular cluster formation and evolution within the cosmological context, highlighting recent observational and simulation advances, and discussing the implications for galaxy assembly and star cluster populations.

Contribution

It provides a comprehensive overview of current understanding, recent progress, and future directions in modeling globular cluster formation during galaxy assembly.

Findings

Old GCs formed around reionisation (≥12.5 Gyr ago)

Detection of multiple stellar populations in young star clusters (~2 Gyr old)

Progress in modeling GC formation reproduces observed scaling relations

Abstract

We discuss some of the key open questions regarding the formation and evolution of globular clusters (GCs) during galaxy formation and assembly within a cosmological framework. The current state-of-the-art for both observations and simulations is described, and we briefly mention directions for future research. The oldest GCs have ages $\ge$ 12.5 Gyr and formed around the time of reionisation. Resolved colour-magnitude diagrams of Milky Way GCs and direct imaging of lensed proto-GCs at z $\sim$ 6 with JWST promise further insight. Globular clusters are known to host multiple populations of stars with variations in their chemical abundances. Recently, such multiple populations have been detected in $\sim$2 Gyr old compact, massive star clusters. This suggests a common, single pathway for the formation of GCs at high and low redshift. The shape of the initial mass function for GCs remains unknown, however for massive galaxies a power-law mass function is favoured. Significant progress has been made recently modelling GC formation in the context of galaxy formation, with success in reproducing many of the observed GC-galaxy scaling relations.