Collision tomography: Physical properties of possible progenitors of the   Andromeda stellar stream
  To unveil a progenitor of the Andromeda Giant Stellar Stream, we investigate the interaction between an accreting satellite galaxy and the Andromeda Galaxy using an $N$-body simulation. A comprehensive parameter study with 247 models is performed by varying size and mass distribution of the progenitor dwarf galaxy. We show that the binding energy of the progenitor is the crucial parameter in reproducing the Andromeda Giant Stellar Stream and the shell-like structures surrounding the Andromeda Galaxy. As a result of the simulations, the progenitor must satisfy a simple scaling relation between the core radius, the total mass and the tidal radius. Using this relation, we successfully constrain the physical properties of the progenitors to have mass ranging from $5\times10^8 M_\odot$ to $5\times10^9 M_\odot$ and central surface density around $10^3\, M_\odot\, \mathrm{pc}^{-2}$. A detailed comparison between our result and the nearby observed galaxies indicates that possible progenitors of the Andromeda Giant Stellar Stream include a dwarf elliptical galaxy, a dwarf irregular galaxy, and a small spiral galaxy. 
Yohei Miki, Masao Mori, and R. Michael Rich
astro-ph.GA