2018MNRAS.473..419B

We determine the escape velocity from the Milky Way (MW) at a range of Galactocentric radii in the context of modified Newtonian dynamics (MOND). Due to its non-linear nature, escape is possible if the MW is considered embedded in a constant external gravitational field (EF) from distant objects. We model this situation using a fully self-consistent method based on a direct solution of the governing equations out to several thousand disc scalelengths. We try out a range of EF strengths and mass models for the MW in an attempt to match the escape velocity measurements of Williams et al. (2017). A reasonable match is found if the EF on the MW is ∼0.03 a0_, towards the higher end of the range considered. Our models include a hot gas corona surrounding the MW, but our results suggest that this should have a very low mass of ∼2 x 10¹⁰ M_☉ to avoid pushing the escape velocity too high. Our analysis favours a slightly lower baryonic disc mass than the ∼7 x 10¹⁰ M_☉ required to explain its rotation curve in MOND. However, given the uncertainties, MOND is consistent with both the locally measured amplitude of the MW rotation curve and its escape velocity over Galactocentric distances of 8-50 kpc.