Mass models of the Milky Way
  We present a simple method for fitting parametrized mass models of the Milky
Way to observational constraints. We take a Bayesian approach which allows us
to take into account input from photometric and kinematic data, and
expectations from theoretical modelling. This provides us with a best-fitting
model, which is a suitable starting point for dynamical modelling. We also
determine a probability density function on the properties of the model, which
demonstrates that the mass distribution of the Galaxy remains very uncertain.
For our choices of parametrization and constraints, we find disc scale lengths
of 3.00 \pm 0.22 kpc and 3.29 \pm 0.56 kpc for the thin and thick discs
respectively; a Solar radius of 8.29 \pm 0.16 kpc and a circular speed at the
Sun of 239 \pm 5 km/s; a total stellar mass of 6.43 \pm 0.63 * 10^10 M_sun; a
virial mass of 1.26 \pm 0.24 * 10^12 M_sun and a local dark matter density of
0.40 \pm 0.04 GeV/cm^3. We find some correlations between the best-fitting
parameters of our models (for example, between the disk scale lengths and the
Solar radius), which we discuss. The chosen disc scale-heights are shown to
have little effect on the key properties of the model.
