Ancient stars beyond the Local Group: RR Lyrae variables and Blue Horizontal Branch stars in Sculptor Group Dwarf Galaxies

TL;DR

This study confirms the presence of ancient stellar populations in Sculptor Group dwarf galaxies through the detection of blue horizontal branch stars and RR Lyrae variables, indicating early star formation in low-density environments.

Contribution

First direct evidence of ancient stars in Sculptor Group dwarf galaxies using Hubble data, expanding understanding of early galaxy evolution beyond the Local Group.

Findings

Blue horizontal branch stars detected in both galaxies

Numerous RR Lyrae variables identified

Evidence of ancient stellar populations beyond the Local Group

Abstract

We have used Hubble Space Telescope ACS images to generate color-magnitude diagrams that reach below the magnitude of the horizontal branch in the Sculptor Group dwarf galaxies ESO294-010 and ESO410-005. In both diagrams blue horizontal branch stars are unambiguously present, a signature of the existence of an ancient stellar population whose age is comparable to that of the Galactic halo globular clusters. The result is reinforced by the discovery of numerous RR Lyrae variables in both galaxies. The occurrence of these stars in the first direct confirmation of the existence of ancient stellar populations beyond the Local Group and indicates that star formation can occur at the earliest epochs even in low density environments.