We present the results of a kinematic survey of the dwarf spheroidal satellite of M31 , Andromeda 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 \sigma _ { v } = 6.8 ^ { +3.0 } _ { -2.0 } { km s ^ { -1 } } , which coupled with the low luminosity implies a very high mass to V -band light ratio , M / L \sim 93 ^ { +120 } _ { -50 } { M _ { \odot } } / { L _ { \odot } } ( M / L > 17 { M _ { \odot } } / { L _ { \odot } } at 99 % confidence ) .
Unless strong tidal forces have perturbed this system , this smallest of galaxies is a highly dark matter dominated system .