Milky Way Mass Models and MOND

TL;DR

This paper tests MOND predictions against the Milky Way's rotation curve using a detailed mass model, finding good agreement without fitting parameters and exploring implications for galaxy structure and interpolation functions.

Contribution

It demonstrates that MOND accurately predicts the Milky Way's rotation curve with a specific mass model and introduces a new interpolation function balancing galaxy and solar system scales.

Findings

MOND matches observed rotation curves without fit parameters.

Short exponential scale lengths (2.0-2.5 kpc) are preferred.

The inverse problem reveals a 'bumpy' mass distribution consistent with observed galaxy features.

Abstract

Using the Tuorla-Heidelberg model for the mass distribution of the Milky Way, I determine the rotation curve predicted by MOND. The result is in good agreement with the observed terminal velocities interior to the solar radius and with estimates of the Galaxy's rotation curve exterior thereto. There are no fit parameters: given the mass distribution, MOND provides a good match to the rotation curve. The Tuorla-Heidelberg model does allow for a variety of exponential scale lengths; MOND prefers short scale lengths in the range 2.0 to 2.5 kpc. The favored value of scale length depends somewhat on the choice of interpolation function. There is some preference for the `simple' interpolation function as found by Famaey & Binney. I introduce an interpolation function that shares the advantages of the simple function on galaxy scales while having a much smaller impact in the solar system. I also solve the inverse problem, inferring the surface mass density distribution of the Milky Way from the terminal velocities. The result is a Galaxy with `bumps and wiggles' in both its luminosity profile and rotation curve that are reminiscent of those frequently observed in external galaxies.