On the Stability of Satellite Planes I: Effects of Mass, Velocity, Halo
  Shape and Alignment
  The recently discovered vast thin plane of dwarf satellites orbiting the
Andromeda Galaxy (M31) adds to the mystery of the small scale distribution of
the Local Group's galaxy population. Such well defined planar structures are
apparently rare occurrences in cold dark matter cosmological simulations, and
we lack a coherent explanation of their formation and existence. In this paper,
we explore the long-term survivability of thin planes of dwarfs in galactic
halos, focusing, in particular, on systems mimicking the observed Andromeda
distribution. The key results show that, in general, planes of dwarf galaxies
are fragile, sensitive to the shape of the dark matter halo and other
perturbing effects. In fact, long lived planes of satellites only exist in
polar orbits in spherical dark matter halos, presenting a challenge to the
observed Andromeda plane which is significantly tilted with respect to the
optical disk. Our conclusion is that, in standard cosmological models, planes
of satellites are generally short lived, and hence we must be located at a
relatively special time in the evolution of the Andromeda Plane, lucky enough
to see its coherent pattern.
