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

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.

11 pages, 2 figures, accepted for publication in Astrophysical Journal Letters

References in corpus (5)

• The ACS Nearby Galaxy Survey Treasury
• The Haunted Halos of Andromeda and Triangulum: A panorama of galaxy formation in action
• The Hubble flow around the CenA / M83 galaxy complex
• Leo A: A Late-Blooming Survivor of the Epoch of Reionization in the Local Group
• The Environmental Influence on the Evolution of Local Galaxies

Cited by in corpus (26)

• The ACS Nearby Galaxy Survey Treasury VIII. The Global Star Formation Histories of 60 Dwarf Galaxies in the Local Volume
• The Star Formation Histories of Local Group Dwarf Galaxies II. Searching For Signatures of Reionization
• Multiplicity of Galactic Cepheids and RR Lyrae stars from Gaia DR2 - I. Binarity from proper motion anomaly
• The Hubble Space Telescope Survey of M31 Satellite Galaxies I. RR Lyrae-based Distances and Refined 3D Geometric Structure
• Dual Stellar Halos in the Standard Elliptical Galaxy M105 and Formation of Massive Early-Type Galaxies
• Probing the early chemical evolution of the Sculptor dSph with purely old stellar tracers
• High-precision distance measurements with classical pulsating stars
• On the Impact of Helium Content on the RR Lyrae Distance Scale
• Weak Galactic Halo--Fornax dSph Connection from RR Lyrae Stars
• The ISLAnds Project III: Variable Stars in Six Andromeda Dwarf Spheroidal Galaxies
• Toward an internally consistent astronomical distance scale
• Chemical Compositions of Field and Globular Cluster RR Lyrae Stars: I. NGC 3201
• Pushing the limits, episode 2: K2 observations of extragalactic RR Lyrae stars in the dwarf galaxy Leo IV
• The properties of dwarf spheroidal galaxies in the Cen A group: Stellar populations, internal dynamics, and a heart-shaped Halpha ring
• MORGOTH: incorporating horizontal branch modelling into star formation history determinations
• Chemical abundances in a high velocity RR Lyrae star near the bulge
• Variable stars in Local Group Galaxies -- V. The fast and early evolution of the low-mass Eridanus II dSph galaxy
• The Early Chemical Enrichment Histories of Two Sculptor Group Dwarf Galaxies as Revealed by RR Lyrae Variables
• On the Metamorphosis of the Bailey diagram for RR Lyrae stars
• A too-many dwarf galaxy satellites problem in the M83 group
• Population gradients and photometric metallicities in early- and transition-type dwarf galaxies: Clues from the Sculptor group
• DELVE-DEEP Survey: The Faint Satellite System of NGC 55
• Satellites in the Local Group and Other Nearby Groups
• The effects of star formation history in the SFR-M relation of HII galaxies
• Zwicky Transient Facility and Globular Clusters: The RR Lyrae gri-Band Period-Luminosity-Metallicity and Period-Wesenheit-Metallicity Relations
• Observational Comparison of Star Formation in Different Galaxy Types