Mass models of the Milky Way

Paul J. McMillan

Published 2011-02-21Version 1

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.