Abstract
We present Keck II/DEIMOS spectroscopy of the three distant dwarf galaxies of M31 Lacerta I, Cassiopeia III, and Perseus I, recently discovered within the Pan-STARRS1 3 pi imaging survey. The systemic velocities of the three systems (nu(r),helio = -198.4 +/- 1.1kms(-1), -371.6 +/- 0.7kms(-1), and -326 +/- 3kms(-1), respectively) confirm that they are satellites of M31. In the case of Lacerta I and Cassiopeia III, the high quality of the data obtained for 126 and 212 member stars, respectively, yields reliable constraints on their global velocity dispersions (sigma(vr) = 10.3 +/- 0.9kms(-1) and 8.4 +/- 0.6kms(-1), respectively), leading to dynamical-mass estimates for both of similar to 4 x 10(7) M-circle dot within their half-light radius. These translate to V-band mass-to-light ratios of 15(-9)(+12) and 8(-5)(+9) in solar units. We also use our spectroscopic data to determine the average metallicity of the three dwarf galaxies ([Fe/H] = -2.0 +/- 0.1, -1.7 +/- 0.1, and -2.0 +/- 0.2, respectively). All these properties are typical of dwarf galaxy satellites of Andromeda with their luminosity and size.