Milky Way potentials in CDM and MOND. Is the Large Magellanic Cloud on a bound orbit?

TL;DR

This paper compares Milky Way potential models in CDM and MOND frameworks, analyzing their shapes and escape velocities, and assesses whether the Large Magellanic Cloud is gravitationally bound under these models.

Contribution

It provides a comparative analysis of Milky Way potentials in CDM and MOND, including predictions of escape velocities and LMC binding conditions.

Findings

MOND potentials are less spherical than CDM potentials.

Predicted escape velocities vary with position in the Galaxy.

LMC can be bound in MOND only with a low external field.

Abstract

We compute the Milky Way potential in different cold dark matter (CDM) based models, and compare these with the modified Newtonian dynamics (MOND) framework. We calculate the axis ratio of the potential in various models, and find that isopotentials are less spherical in MOND than in CDM potentials. As an application of these models, we predict the escape velocity as a function of the position in the Galaxy. This could be useful in comparing with future data from planned or already-underway kinematic surveys (RAVE, SDSS, SEGUE, SIM, GAIA or the hypervelocity stars survey). In addition, the predicted escape velocity is compared with the recently measured high proper motion velocity of the Large Magellanic Cloud (LMC). To bind the LMC to the Galaxy in a MOND model, while still being compatible with the RAVE-measured local escape speed at the Sun's position, we show that an external field modulus of less than $0.03 a_0$ is needed.