A Keck/DEIMOS spectroscopic survey of the faint M31 satellites And IX, And XI, And XII and And XIII†

We present the first spectroscopic analysis of the faint M31 satellite galaxies, And XI and And XIII, as well as a re-analysis of existing spectroscopic data for two further faint compan-ions, And IX (correcting for an error in earlier geometric modelling that caused a misclassifi-cation of member stars in previous work) and And XII. By combining data obtained using the Deep Imaging Multi-Object Spectrograph (DEIMOS) mounted on the Keck II telescope with deep photometry from the Suprime-Cam instrument on Subaru, we have identified the most probable members for each of the satellites based on their radial velocities (precise to several km s−1 down to i ∼ 22), distance from the centre of the dwarf spheroidal galaxies (dSphs) and their photometric [Fe/H]. Using both the photometric and spectroscopic data, we have also calculated global properties for the dwarfs, such as systemic velocities, metallicities and half-light radii. We find each dwarf to be very metal poor ([Fe/H] ∼ −2 both photometrically and spectroscopically, from their stacked spectrum), and as such, they continue to follow the luminosity–metallicity relationship established with brighter dwarfs. We are unable to resolve dispersion for And XI due to small sample size and low signal-to-noise ratio, but we set