Equilibrium models of the Milky Way mass are biased high by the LMC

Abstract

Recent measurements suggest that the Large Magellanic Cloud (LMC) may weigh as much as 25\% of the Milky Way. In this work we explore how such a large satellite affects mass estimates of the Milky Way based on equilibrium modelling of the stellar halo or other tracers. In particular, we show that if the LMC is ignored, the Milky Way mass is overestimated by as much as 50\%. This bias is due to the bulk motion in the outskirts of the Galaxy's halo and can be, at least in part, accounted for with a simple modification to the equilibrium modelling. Finally, we show that the LMC has a substantial effect on the orbit Leo I which acts to increase its present day speed relative to the Milky Way. We estimate that accounting for a $1.5\times 10^{11}{M}_{\odot }$ LMC would lower the inferred Milky Way mass to $\sim 10^{12}{M}_{\odot }$.

arXiv comment7 pages, 6 figures. Submitted to MNRAS. Comments welcome

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