A new determination of the local dark matter density from the kinematics of K dwarfs

• Main Authors: Garbari, Silvia, Liu, Chao, Read, Justin I, Lake, George
• Format: Journal Article
• Language: English
• Published: 23-07-2012
• Subjects: Physics - Astrophysics of Galaxies
• DOI: 10.48550/arxiv.1206.0015

MNRAS 425, p 1445 (2012) We apply a new method to determine the local disc matter and dark halo matter
density to kinematic and position data for \sim2000 K dwarf stars taken from
the literature. Our method assumes only that the disc is locally in dynamical
equilibrium, and that the 'tilt' term in the Jeans equations is small up to
\sim1 kpc above the plane. We present a new calculation of the photometric
distances to the K dwarf stars, and use a Monte Carlo Markov Chain to
marginalise over uncertainties in both the baryonic mass distribution, and the
velocity and distance errors for each individual star. We perform a series of
tests to demonstrate that our results are insensitive to plausible systematic
errors in our distance calibration, and we show that our method recovers the
correct answer from a dynamically evolved N-body simulation of the Milky Way.
We find a local dark matter density of {\rho}dm = 0.025+0.014-0.013
M\odotpc^{-3} (0.95+0.53-0.49 GeV cm^{-3}) at 90% confidence assuming no
correction for the non-flatness of the local rotation curve, and {\rho}dm =
0.022+0.015-0.013 M\odotpc^-3 (0.85+0.57-0.50 GeV cm^{-3}) if the correction is
included. Our 90% lower bound on {\rho}dm is larger than the canonical value
typically assumed in the literature, and is at mild tension with extrapolations
from the rotation curve that assume a spherical halo. Our result can be
explained by a larger normalisation for the local Milky Way rotation curve, an
oblate dark matter halo, a local disc of dark matter, or some combination of
these.