Weighing the local dark matter with RAVE red clump stars
  We determine the Galactic potential in the solar neigbourhood from RAVE
observations. We select red clump stars for which accurate distances, radial
velocities, and metallicities have been measured. Combined with data from the
2MASS and UCAC catalogues, we build a sample of 4600 red clump stars within a
cylinder of 500 pc radius oriented in the direction of the South Galactic Pole,
in the range of 200 pc to 2000 pc distances. We deduce the vertical force and
the total mass density distribution up to 2 kpc away from the Galactic plane by
fitting a distribution function depending explicitly on three isolating
integrals of the motion in a separable potential locally representing the
Galactic one with four free parameters. Because of the deep extension of our
sample, we can determine nearly independently the dark matter mass density and
the baryonic disc surface mass density. We find (i) at 1kpc Kz/(2piG) = 68.5 pm
1.0 Msun/pc2, and (ii) at 2 kpc Kz/(2piG) = 96.9 pm 2.2 Msun/pc2. Assuming the
solar Galactic radius at R0 = 8.5 kpc, we deduce the local dark matter density
rhoDM (z=0) = 0.0143 pm 0.0011Msun pc3 = 0.542 pm 0.042 Gev/cm3 and the
baryonic surface mass density Sigma = 44.4 pm 4.1 Msun/pc2 . Our results are in
agreement with previously published Kz determinations up to 1 kpc, while the
extension to 2 kpc shows some evidence for an unexpectedly large amount of dark
matter. A flattening of the dark halo of order 0.8 can produce such a high
local density in combination with a circular velocity of 240 km/s . Another
explanation, allowing for a lower circular velocity, could be the presence of a
secondary dark component, a very thick disc resulting either from the deposit
of dark matter from the accretion of multiple small dwarf galaxies, or from the
presence of an effective phantom thick disc in the context of effective
galactic-scale modifications of gravity.
