A Relic Star Cluster in the Sextans Dwarf Spheroidal Galaxy - Implications for Early Star and Galaxy Formation

TL;DR

This paper provides evidence for a dissolved ancient star cluster in the Sextans dwarf galaxy, revealing insights into early star formation and galaxy evolution, and proposing a new interpretation of metallicity functions in dwarf galaxies.

Contribution

It reports the potential discovery of the most metal-poor star cluster and introduces a novel approach to understanding metallicity distributions in dwarf galaxies.

Findings

Identification of a chemically clustered star group at [Fe/H] = -2.7

Estimated initial mass of the star cluster is around 1.9 x 10^5 solar masses

Proposes different formation environments for ultra-faint and classical dwarf galaxies

Abstract

We present tentative evidence for the existence of a dissolved star cluster in the Sextans dwarf spheroidal galaxy. In a sample of six stars, we identify three (possibly four) stars around [Fe/H] =-2.7 that are highly clustered in a multi-dimensional chemical abundance space. The estimated initial stellar mass of the cluster is M*,init = 1.9^+1.5_-0.9 (1.6^+1.2_-0.8)*10^5 Msol assuming a Salpeter (Kroupa) initial mass function (IMF). If corroborated by follow-up spectroscopy, this ancient star cluster at [Fe/H] =-2.7 is the most metal-poor system identified to date. Inspired by this finding, we also present a new way to interpret the cumulative metallicity functions of dwarf galaxies. From available observational data, we speculate that the ultra-faint dwarf galaxy population, or a significant fraction thereof, and the more luminous, classical dwarf spheroidal population were formed in different environments and would thus be distinct in origin.