Andromeda XXIX: A new dwarf spheroidal galaxy 200kpc from Andromeda

Abstract

We report the discovery of a new dwarf galaxy, Andromeda XXIX (And XXIX), using data from the recently released Sloan Digital Sky Survey Data Release 8, and confirmed by Gemini North telescope Multi-Object Spectrograph imaging data. And XXIX appears to be a dwarf spheroidal galaxy, separated on the sky by a little more than 15°from M31, with a distance inferred from the tip of the red giant branch of 730 ± 75kpc, corresponding to a three-dimensional separation from M31 of 207+20-2kpc (close to M31's virial radius). Its absolute magnitude, as determined by comparison to the red giant branch luminosity function of the Draco dwarf spheroidal, is MV = -8.3 ± 0.4. And XXIX's stellar populations appear very similar to Draco's; consequently, we estimate a metallicity for And XXIX of [Fe/H] ∼-1.8. The half-light radius of And XXIX is 360 ± 60pc and its ellipticity is 0.35 ± 0.06, typical of dwarf satellites of the Milky Way and M31 at this absolute magnitude range. © 2011. The American Astronomical Society. All rights reserved..