Resolving the Stellar Outskirts of M31 and M33
  Many clues about the galaxy assembly process lurk in the faint outer regions of galaxies. The low surface brightnesses of these parts pose a significant challenge for studies of diffuse light, and few robust constraints on galaxy formation models have been derived to date from this technique. Our group has pioneered the use of extremely wide-area star counts to quantitatively address the large-scale structure and stellar content of external galaxies at very faint light levels. We highlight here some results from our imaging and spectroscopic surveys of M31 and M33. 
Annette Ferguson, Mike Irwin, Scott Chapman, Rodrigo Ibata, Geraint   Lewis, Nial Tanvir