Abstract
We apply the vertical Jeans equation to the kinematics of Milky Way stars in the solar
neighbourhood to measure the local dark matter density. More than 90,000 G- and
K-type dwarf stars are selected from the cross-matched sample of LAMOST DR5 and
Gaia DR2 for our analyses. The mass models applied consist of a single exponential
stellar disc, a razor thin gas disc and a constant dark matter density. We first con-
sider the simplified vertical Jeans equation which ignores the tilt term and assumes
a flat rotation curve. Under a Gaussian prior on the total stellar surface density, the
local dark matter density inferred from Markov Chain Monte Carlo simulations is
+0.0024 M pc −3 . The local dark matter densities for subsamples in an azimuthal
0.0133 −0.0022
angle range of −10 ◦ < φ < 5 ◦ are consistent within their 1σ errors. However, the
northern and southern subsamples show a large discrepancy due to plateaux in the
northern and southern vertical velocity dispersion profiles. These plateaux may be
the cause of the different estimates of the dark matter density between the north and
south. Taking the tilt term into account has little effect on the parameter estimations
and does not explain the north and south asymmetry. Taking half of the difference
of σ z profiles as unknown systematic errors, we then obtain consistent measurements
for the northern and southern subsamples. We discuss the influence of the vertical
data range, the scale height of the tracer population, the vertical distribution of stars
and the sample size on the uncertainty of the determination of the local dark matter
density.
Original language | English |
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Journal | MNRAS |
Publication status | Accepted/In press - 18 May 2020 |