The large-scale structure of the halo of the Andromeda Galaxy Part I:
  global stellar density, morphology and metallicity properties
  We present an analysis of the large-scale structure of the halo of the
Andromeda galaxy, based on the Pan-Andromeda Archeological Survey (PAndAS),
currently the most complete map of resolved stellar populations in any galactic
halo. Despite copious substructure, the global halo populations follow closely
power law profiles that become steeper with increasing metallicity. We divide
the sample into stream-like populations and a smooth halo component. Fitting a
three-dimensional halo model reveals that the most metal-poor populations
([Fe/H]<-1.7) are distributed approximately spherically (slightly prolate with
ellipticity c/a=1.09+/-0.03), with only a relatively small fraction (42%)
residing in discernible stream-like structures. The sphericity of the ancient
smooth component strongly hints that the dark matter halo is also approximately
spherical. More metal-rich populations contain higher fractions of stars in
streams (86% for [Fe/H]>-0.6). The space density of the smooth metal-poor
component has a global power-law slope of -3.08+/-0.07, and a non-parametric
fit shows that the slope remains nearly constant from 30kpc to 300kpc. The
total stellar mass in the halo at distances beyond 2 degrees is 1.1x10^10 Solar
masses, while that of the smooth component is 3x10^9 Solar masses.
Extrapolating into the inner galaxy, the total stellar mass of the smooth halo
is plausibly 8x10^9 Solar masses. We detect a substantial metallicity gradient,
which declines from [Fe/H]=-0.7 at R=30kpc to [Fe/H]=-1.5 at R=150kpc for the
full sample, with the smooth halo being 0.2dex more metal poor than the full
sample at each radius. While qualitatively in-line with expectations from
cosmological simulations, these observations are of great importance as they
provide a prototype template that such simulations must now be able to
reproduce in quantitative detail.
