The nature of the progenitor of the M31 North-western stream: globular
  clusters as milestones of its orbit
  We examine the nature, possible orbits and physical properties of the
progenitor of the North-western stellar stream (NWS) in the halo of the
Andromeda galaxy (M31). The progenitor is assumed to be an accreting dwarf
galaxy with globular clusters (GCs). It is, in general, difficult to determine
the progenitor's orbit precisely because of many necessary parameters.
Recently, Veljanoski et al. 2014 reported five GCs whose positions and radial
velocities suggest an association with the stream. We use this data to
constrain the orbital motions of the progenitor using test-particle
simulations. Our simulations split the orbit solutions into two branches
according to whether the stream ends up in the foreground or in the background
of M31. Upcoming observations that will determine the distance to the NWS will
be able to reject one of the two branches. In either case, the solutions
require that the pericentric radius of any possible orbit be over 2 kpc. We
estimate the efficiency of the tidal disruption and confirm the consistency
with the assumption for the progenitor being a dwarf galaxy. The progenitor
requires the mass $\ga 2\times10^6 M_{\sun}$ and half-light radius $\ga 30$ pc.
In addition, $N$-body simulations successfully reproduce the basic observed
features of the NWS and the GCs' line-of-sight velocities.
