Globular Clusters in High-Redshift Dwarf Galaxies: A Case Study from the Local Group

TL;DR

This study reconstructs the UV luminosity evolution of Fornax's globular clusters and suggests they could be mistaken for faint galaxies in high-redshift observations, impacting galaxy formation models.

Contribution

It provides the first detailed analysis of the UV evolution of dwarf galaxy GCs and highlights their potential role as proto-GCs in the early Universe.

Findings

Fornax's GCs can produce 10-100 times more UV flux than the field stars.

Faint compact sources in HFFs may be GCs, not galaxies.

GC formation can cause significant errors in abundance matching.

Abstract

We present the reconstructed evolution of rest-frame ultra-violet (UV) luminosities of the most massive Milky Way dwarf spheroidal satellite galaxy, Fornax, and its five globular clusters (GCs) across redshift, based on analysis of the stellar fossil record and stellar population synthesis modeling. We find that (1) Fornax's (proto-)GCs can generate $10-100$ times more UV flux than the field population, despite comprising $<\sim 5\%$ of the stellar mass at the relevant redshifts; (2) due to their respective surface brightnesses, it is more likely that faint, compact sources in the Hubble Frontier Fields (HFFs) are GCs hosted by faint galaxies, than faint galaxies themselves. This may significantly complicate the construction of a galaxy UV luminosity function at $z>3$. (3) GC formation can introduce order-of-magnitude errors in abundance matching. We also find that some compact HFF objects are consistent with the reconstructed properties of Fornax's GCs at the same redshifts (e.g., surface brightness, star formation rate), suggesting we may already have detected proto-GCs in the early Universe. Finally, we discuss the prospects for improving the connections between local GCs and proto-GCs detected in the early Universe.