Could M31 be the result of a major merger?
  We investigated a scenario in which M31 could be the remnant of a gas-rich major merger. Galaxy merger simulations, highly constrained by observations, were run using GADGET 2 in order to reproduce M31. We succeeded in reproducing the global shape of M31, the thin disk and the bulge, and in addition some of the main M31 large-scale features, such as the thick disk, the 10kpc ring and the Giant Stream. This lead to a new explanation of the Giant Stream which could be caused by tidal tail stars that have been captured by the galaxy potential. 
Sylvain Fouquet, Fran\c{c}ois Hammer, Yang-Bin Yang, Jianling Wang,   Mathieu Puech and Hector Flores
astro-ph.CO