Dark Halos of M31 and the Milky Way
  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.
