The mass of the Milky Way out to 100 kpc using halo stars

Abstract

We use a distribution function analysis to estimate the mass of the Milky Way (MW) out to 100 kpc using a large sample of halo stars. These stars are compiled from the literature, and the vast majority (∼ } 98{{\ \rm per\ cent}}) have 6D phase-space information. We pay particular attention to systematic effects, such as the dynamical influence of the Large Magellanic Cloud (LMC), and the effect of unrelaxed substructure. The LMC biases the (pre-LMC infall) halo mass estimates towards higher values, while realistic stellar haloes from cosmological simulations tend to underestimate the true halo mass. After applying our method to the MW data, we find a mass within 100 kpc of M (<100 kpc) = 6.07 ± 0.29 (stat.) ± 1.21 (sys.) × 1011 MO. For this estimate, we have approximately corrected for the reflex motion induced by the LMC using the Erkal et al. model, which assumes a rigid potential for the LMC and MW. Furthermore, stars that likely belong to the Sagittarius stream are removed, and we include a 5 per cent systematic bias, and a 20 per cent systematic uncertainty based on our tests with cosmological simulations. Assuming the mass-concentration relation for Navarro-Frenk-White haloes, our mass estimate favours a total (pre-LMC infall) MW mass of M200c = 1.01 ± 0.24 × 1012 MO, or (post-LMC infall) mass of M200c = 1.16 ± 0.24 × 1012 MO when a 1.5 × 1011 MO mass of a rigid LMC is included.