G. S. Da Costa et al. 2010 ApJ 708 L121 doi:10.1088/2041-8205/708/2/L121
G. S. Da Costa1, M. Rejkuba2, H. Jerjen1 and E. K. Grebel3
Show affiliationsWe have used Hubble Space Telescope Advanced Camera for Surveys 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 is 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.
galaxies: dwarf; galaxies: individual (ESO 294-010, ESO 410-005); galaxies: stellar content; stars: horizontal-branch; stars: variables: other
Issue 2 (2010 January 10)
Received 2009 October 27, accepted for publication 2009 December 4
Published 2009 December 22
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