While the satellites of the Milky Way (MW) have been shown to be largely
consistent in terms of their mass contained within one half--light radius
(M_{half}) with a "Universal" mass profile, a number of M31 satellites are
found to be inconsistent with such relations, and seem kinematically colder in
their central regions than their MW cousins. In this work, we present new
kinematic and updated structural properties for two M31 dSphs, And V and And VI
using data from the Keck Low Resolution Imaging Spectrograph (LRIS) and the
DEep Imaging Multi-Object Spectrograph (DEIMOS) instruments and the Subaru
Suprime-Cam imager. We measure systemic velocities of v_r=-393.1+/-4.2km/s and
-344.8+/-2.5km/s, and dispersions of sigma_v=11.5{+5.3}{-4.4}km/s and
sigma_v=9.4{+3.2}{-2.4}km/s for And V and And VI respectively, meaning these
two objects are consistent with the trends in sigma_v and r_{half} set by their
MW counterparts. We also investigate the nature of this scatter about the MW
dSph mass profiles for the "Classical" (i.e. M_V<-8) MW and M31 dSphs. When
comparing both the "classical" MW and M31 dSphs to the best--fit mass profiles
in the size--velocity dispersion plane, we find general scatter in both the
positive (i.e. hotter) and negative (i.e. colder) directions from these
profiles. However, barring one exception (CVnI) only the M31 dSphs are found to
scatter towards a colder regime, and, excepting the And I dSph, only MW objects
scatter to hotter dispersions. We also note that the scatter for the combined
population is greater than expected from measurement errors alone. We assess
this divide in the context of the differing disc-to-halo mass (i.e. stars and
baryons to total virial mass) ratios of the two hosts and argue that the
underlying mass profiles for dSphs differ from galaxy to galaxy, and are
modified by the baryonic component of the host.Comment: 15 pages, 8 figures. Small modifications made for referee report.
Accepted for publication in MNRAS (29/06/2011
