Dark Halos of M31 and the Milky Way

TL;DR

This study constructs and analyzes the rotation curves of M31 and the Milky Way to compare their mass distributions, revealing similar disk and bulge structures but a more massive dark halo in M31, supporting the NFW model.

Contribution

The paper provides a detailed comparison of dark matter halos in M31 and the Milky Way using revised rotation curves and NFW profile fitting, highlighting differences in dark halo mass.

Findings

M31's dark halo is twice as massive as the Milky Way's.

Both galaxies have similar disk and bulge structures.

The NFW profile effectively models the observed dark halos.

Abstract

Grand rotation curves (GRC) within ~400 kpc of M31 and the Milky Way were constructed by combining disk rotation velocities and radial velocities of satellite galaxies and globular clusters. The GRC for the Milky Way was revised using the most recent Solar rotation velocity. The derived GRCs were deconvolved into a de Vaucouleurs bulge, exponential disk, and a dark halo with the Navarro-Frenk-White (NFW) density profile by the least chi-squares fitting. Comparison of the best-fit parameters revealed similarity of the disks and bulges of the two galaxies, whereas the dark halo mass of M31 was found to be twice the Galaxy's. We show that the NFW model may be a realistic approximation to the observed dark halos in these two giant spirals.