The Escape Velocity Curve of the Milky Way in Modified Newtonian Dynamics

TL;DR

This study models the Milky Way's escape velocity in the context of Modified Newtonian Dynamics (MOND), considering external gravitational fields, and finds consistency with observed escape velocities and rotation curves.

Contribution

It presents a self-consistent method to calculate the Milky Way's escape velocity in MOND, incorporating external fields and comparing results with observational data.

Findings

A reasonable external field strength is about 0.03 a0.

A low-mass hot gas corona (~2x10^10 M_sun) fits the escape velocity data.

MOND can explain both the rotation curve and escape velocity within uncertainties.

Abstract

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 disk scale lengths. 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 ${\sim 0.03 a_{_0}}$, 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 ${\sim 2 \times 10^{10} M_\odot}$ to avoid pushing the escape velocity too high. Our analysis favours a slightly lower baryonic disk mass than the ${\sim 7 \times 10^{10} M_\odot}$ 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.