The prolate dark matter halo of the Andromeda galaxy
  We present new limits on the global shape of the dark matter halo in the
Andromeda galaxy using and generalizing non-spherical mass models developed by
Hayashi & Chiba and compare our results with theoretical predictions of cold
dark matter (CDM) models. This is motivated by the fact that CDM models predict
non-spherical virialized dark halos, which reflect the process of mass assembly
in the galactic scale. Applying our models to the latest kinematic data of
globular clusters and dwarf spheroidal galaxies in the Andromeda halo, we find
that the most plausible cases for Andromeda yield a prolate shape for its dark
halo, irrespective of assumed density profiles. We also find that this prolate
dark halo in Andromeda is consistent with theoretical predictions in which the
satellites are distributed anisotropically and preferentially located along
major axes of their host halos. It is a reflection of the intimate connection
between galactic dark matter halos and the cosmic web. Therefore, our result is
profound in understanding internal dynamics of halo tracers in Andromeda, such
as orbital evolutions of tidal stellar streams, which play important roles in
extracting the abundance of CDM subhalos through their dynamical effects on
stream structures.
