M31 Satellite Masses Compared to LCDM Subhaloes
  We compare the kinematics of M31's satellite galaxies to the mass profiles of
the subhaloes they are expected to inhabit in LCDM. We consider the most
massive subhaloes of an approximately M31-sized halo, following the assumption
of a monotonic galaxy luminosity-to-subhalo mass mapping. While this abundance
matching relation is consistent with the kinematic data for galaxies down to
the luminosity of the bright satellites of the Milky Way and M31, it is not
consistent with kinematic data for fainter dwarf galaxies (those with L <~ 10^8
Lsun). Comparing the kinematics of M31's dwarf Spheroidal (dSph) satellites to
the subhaloes reveals that M31's dSph satellites are too low density to be
consistent with the subhaloes' mass profiles. A similar discrepancy has been
reported between Milky Way dSphs and their predicted subhaloes, the "too big to
fail" problem. By contrast, total mass profiles of the dwarf Elliptical (and
similarly bright) satellites are consistent with the subhaloes. However, they
suffer from large systematic uncertainties in their dark matter content because
of substantial (and potentially dominant) contributions from baryons within
their half-light radii.
