Structural parameters for the M31 dwarf spheroidals
  (Abridged) The projected structures and integrated properties of the Andromeda I, II, III, V, VI, VII and Cetus dwarf spheroidal galaxies are analysed based upon resolved counts of red giant branch stars. For each object, we have derived isopleth maps, surface brightness profiles, absolute magnitudes, central surface brightnesses, and a large number of other morphological parameters. Our analysis probes to larger radius and fainter surface brightnesses than most previous studies and as a result we find that the galaxies are generally larger and brighter than has previously been recognised. In particular, the luminosity of Andromeda V is found to be consistent with the higher metallicity value which has been derived for it. Andromeda I shows strong evidence of tidal disruption and S-shaped tidal tails are clearly visible. On the other hand, Cetus does not show any evidence of tidal truncation, let alone disruption. Andromeda II shows compelling evidence of a large excess of stars at small radius and suggests that this galaxy consists of a secondary core component. Comparing the M31 dwarf spheroidal population with the Galactic population, we find that the scale radii of the M31 population are larger than those for the Galactic population by at least a factor of two, for all absolute magnitudes. We also find that the two populations are offset from one another in the central surface brightness - luminosity relation. Finally, we find that the M31 dwarf spheroidals show the same correlation with distance-from-host as shown by the Galactic population, such that dwarf spheroidals with a higher central surface brightness are found further from their host. This again suggests that environment plays a significant role in dwarf galaxy evolution. 
Alan McConnachie, Mike Irwin