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.
