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 these 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 \pm 4.2 { km s ^ { -1 } } and -344.8 \pm 2.5 { km s ^ { -1 } } , and dispersions of \sigma _ { v } = 11.5 ^ { +5.3 } _ { -4.4 } { km s ^ { -1 } } and \sigma _ { v } = 9.4 ^ { +3.2 } _ { -2.4 } { km s ^ { -1 } } 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 .
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 .