2005ApJ...632L..87C

We present the results of a kinematic survey of the dwarf spheroidal satellite of M31, And IX, which appears to be the lowest surface brightness and also the faintest galaxy (M_V=-8.3) found to date. Using Keck DEIMOS spectroscopic data, we have measured its velocity relative to M31, its velocity dispersion, and its metallicity. It exhibits a significant velocity dispersion σ_v=6.8^+3.0_–2.0 km/s, which coupled with the low luminosity implies a very high mass-to-V-band light ratio, M/L∼93⁺¹²⁰_–50M_☉/L_☉(M/L>17 M_☉/L_☉ at 99% confidence). Unless strong tidal forces have perturbed this system, this smallest of galaxies is a highly dark matter-dominated system.