We present a homogeneous kinematic analysis of red giant branch stars within 18 of the 28 Andromeda dwarf spheroidal ( dSph ) galaxies , obtained using the Keck I LRIS and Keck II DEIMOS spectrographs .
Based on their g - i colors ( taken with the CFHT MegaCam imager ) , physical positions on the sky , and radial velocities , we assign probabilities of dSph membership to each observed star .
Using this information , the velocity dispersions , central masses and central densities of the dark matter halos are calculated for these objects , and compared with the properties of the Milky Way dSph population .
We also measure the average metallicity ( [ Fe/H ] ) from the co-added spectra of member stars for each M31 dSph and find that they are consistent with the trend of decreasing [ Fe/H ] with luminosity observed in the Milky Way population .
We find that three of our studied M31 dSphs appear as significant outliers in terms of their central velocity dispersion , And XIX , XXI and XXV , all of which have large half-light radii ( \mathrel { \hbox to 0.0 pt { \lower 3.0 pt \hbox { $ \mathchar 536 $ } \hss } \raise 2.0 pt% \hbox { $ \mathchar 318 $ } } 700 pc ) and low velocity dispersions ( \sigma _ { v } < 5 { km s ^ { -1 } } ) .
In addition , And XXV has a mass-to-light ratio within its half-light radius of just [ M / L ] _ { half } = 10.3 ^ { +7.0 } _ { -6.7 } , making it consistent with a simple stellar system with no appreciable dark matter component within its 1 \sigma uncertainties .
We suggest that the structure of the dark matter halos of these outliers have been significantly altered by tides .