The mass distribution and gravitational potential of the Milky Way

Abstract

We present mass models of the Milky Way created to fit observational\nconstraints and to be consistent with expectations from theoretical modelling.\nThe method used to create these models is that demonstrated in McMillan (2011),\nand we improve on those models by adding gas discs to the potential,\nconsidering the effects of allowing the inner slope of the halo density profile\nto vary, and including new observations of maser sources in the Milky Way\namongst the new constraints. We provide a best fitting model, as well as\nestimates of the properties of the Milky Way. Under the assumptions in our main\nmodel, we find that the Sun is $R_0 = (8.20\\pm0.09)\\,\\mathrm{kpc}$ from the\nGalactic Centre, with the circular speed at the Sun being $v_0 =\n(232.8\\pm3.0)\\,\\mathrm{km}\\,\\mathrm{s}^{-1}$; that the Galaxy has a total\nstellar mass of $(54.3\\pm5.7)\\times10^9\\,{\\rm M}_\\odot$, a total virial mass of\n$(1.30 \\pm 0.30)\\times10^{12}\\,{\\rm M}_\\odot$ and a local dark-matter density\nof $0.38\\pm0.04\\,\\mathrm{GeV\\,cm}^{-3}$, where the quoted uncertainties are\nstatistical. These values are sensitive to our choice of priors and\nconstraints. We investigate systematic uncertainties, which in some cases may\nbe larger. For example, if we weaken our prior on $R_0$, we find it to be\n$(7.97\\pm0.15)\\,\\mathrm{kpc}$ and that\n$v_0=(226.8\\pm4.2)\\,\\mathrm{km}\\,\\mathrm{s}^{-1}$. We find that most of these\nproperties, including the local dark-matter density, are remarkably insensitive\nto the assumed power-law density slope at the centre of the dark-matter halo.\nWe find that it is unlikely that the local standard of rest differs\nsignificantly from that found under assumptions of axisymmetry. We have made\ncode to compute the force from our potential, and to integrate orbits within\nit, publicly available.\n