The mass of our Galaxy from satellite proper motions in the Gaia era

We use Gaia DR2 systemic proper motions of 45 satellite galaxies to constrain the mass of the MilkyWay using the scale-free mass estimator ofWatkins et al. (2010). We first determine the anisotropy parameter beta, and the tracer satellites' radial density index gamma to be beta =-0.67(-0.62)(+0.45) and gamma = 2.11 +/- 0.23. When we exclude possible former satellites of the Large Magellanic Cloud, the anisotropy changes to beta = -0.21(-0.51)(+0.37). We find that the index of the Milky Way's gravitational potential alpha, which is dependent on themass itself, is the parameter with the largest impact on the mass determination. Via comparison with cosmological simulations of Milky Way-like galaxies, we carried out a detailed analysis of the estimation of the observational uncertainties and their impact on themass estimator. We found that themass estimator is biased when applied naively to the satellites of simulated MilkyWay haloes. Correcting for this bias, we obtain for our Galaxy a mass of 0.58(-0.14)(+0.15) x 10(12)M(circle dot) within 64 kpc, as computed from the inner half of our observational sample, and 1.43(-0.32)(+0.35) x 10(2)(1)M(circle dot) within 273 kpc, from the full sample; this latter value extrapolates to a virial mass of M-vir Delta=97 = 1.51(-0.40)(+0.45) x 10(12)M(circle dot) corresponding to a virial radius of R-vir = 308 +/- 29 kpc. This value of the MilkyWay mass lies in-between other mass estimates reported in the literature, from various different methods.