ANDROMEDA XXIX: A NEW DWARF SPHEROIDAL GALAXY 200 kpc FROM ANDROMEDA

摘要

We report the discovery of a newdwarf 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 ± 75 kpc, corresponding to a threedimensional separation fromM31 of 207_(-2)~(+20) kpc (close to M31’s virial radius). Its absolutemagnitude, as determined by comparison to the red giant branch luminosity function of the Draco dwarf spheroidal, isM_V = -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 ± 60 pc and its ellipticity is 0.35 ± 0.06, typical of dwarf satellites of the Milky Way and M31 at this absolute magnitude range.