The outer limits of the M31 system: Kinematics of the dwarf galaxy satellites and XXVIII & and XXIX

Abstract

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-1 and a velocity dispersion of 4.9 ± 1.6 km s-1, 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-1 and velocity dispersion of 5.7 ± 1.2 km s-1, 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. © 2013. The American Astronomical Society. All rights reserved.