Hubble Space TelescopePhotometry of the Dwarf Spheroidal Galaxy ESO 410‐G005

Abstract

We present Hubble Space Telescope WFPC2 imaging of the nearby low surface brightness dwarf spheroidal galaxy ESO 410-G005, which has been resolved into stars for the first time. The resulting color-magnitude diagram for about 2500 stars shows a red giant branch with a tip at I = 22.4 ± 0.15 mag, which yields a distance of DMW = 1.9 ± 0.2 Mpc. ESO 410-G005 is found to be metal-poor with a mean metallicity of ⟨[Fe/H]⟩ = (-1.8 ± 0.4) dex estimated from its red giant branch. Upper asymptotic giant branch stars appear to be present near the center of the galaxy, indicative of a substantial, centrally concentrated intermediate-age population, unless these objects are artifacts of crowding. Previous studies did not detect ESO 410-G005 in Hα or in H I. Based on our distance estimate, ESO 410-G005 is a probable member of the Sculptor group of galaxies. Its linear separation from the nearest spiral, NGC 55, is 230 kpc on the sky. The deprojected separation ranges from 340 to 615 kpc depending on the assumed distance of NGC 55. The deprojected distance from the Sculptor group spiral NGC 300 is (385 ± 200) kpc. ESO 410-G005 appears to be a relatively isolated dSph within the Sculptor group. Its absolute magnitude, MV,0 = -12.1 ± 0.2 mag, its central surface brightness, μV,0 = 22.7 ± 0.1 mag arcsec-2, and its mean metallicity, [Fe/H] = (-1.8 ± 0.4) dex follow the trend observed for dwarf galaxies in the Local Group.