On the Local Dark Matter Density
Abstract
An analysis of the kinematics of 412 stars at 14 kpc from the Galactic midplane by Moni Bidin et al. has claimed to derive a local density of dark matter that is an order of magnitude below standard expectations. We show that this result is incorrect and that it arises from the assumption that the mean azimuthal velocity of the stellar tracers is independent of Galactocentric radius at all heights. We substitute the assumption, supported by data, that the circular speed is independent of radius in the midplane. We demonstrate that the assumption of constant mean azimuthal velocity is implausible by showing that it requires the circular velocity to drop more steeply than allowed by any plausible mass model, with or without dark matter, at large heights above the midplane. Using the approximation that the circularvelocity curve is flat in the midplane, we find that the data imply a local dark matter density of 0.008 ± 0.003 M _{⊙} pc^{3} = 0.3 ± 0.1 GeV cm^{3}, fully consistent with standard estimates of this quantity. This is the most robust direct measurement of the local dark matter density to date.
 Publication:

The Astrophysical Journal
 Pub Date:
 September 2012
 DOI:
 10.1088/0004637X/756/1/89
 arXiv:
 arXiv:1205.4033
 Bibcode:
 2012ApJ...756...89B
 Keywords:

 Galaxy: disk;
 Galaxy: fundamental parameters;
 Galaxy: halo;
 Galaxy: kinematics and dynamics;
 Galaxy: structure;
 solar neighborhood;
 Astrophysics  Galaxy Astrophysics;
 Astrophysics  Cosmology and Extragalactic Astrophysics;
 High Energy Physics  Phenomenology
 EPrint:
 ApJ, in press