2013ApJ...768...50T

We present Keck/DEIMOS spectroscopy of resolved stars in the M31 satellites And XXVIII and And XXIX. We show that these are likely self-bound galaxies based on 18 and 24 members in And XXVIII and And XXIX, respectively. And XXVIII has a systemic velocity of -331.1±1.8 km/s and a velocity dispersion of 4.9±1.6 km/s, implying a mass-to-light ratio (within r_1/2) of ∼44±41. And XXIX has a systemic velocity of -194.4±1.5 km/s and velocity dispersion of 5.7±1.2 km/s, implying a mass-to-light ratio (within r_1/2) of ∼124±72. The internal kinematics and implied masses of And XXVIII and And XXIX are similar to those of dwarf spheroidals (dSphs) of comparable luminosities, implying that these objects are dark-matter-dominated dwarf galaxies. Despite the large projected distances from their host (380 and 188 kpc), the kinematics of these dSph suggest that they are bound M31 satellites.