The mass of the Galactic dark matter halo from ∼9000 LAMOST DR5 K giants

Abstract

We constrain the mass of the Milky Wayʼs dark matter halo, based on the kinematics of 9627 K giants at Galactocentric distances ranging over 5 kpc drawn from LAMOST DR5. The substructure in this sample has been identified and removed carefully to enable construction of the underlying line-of-sight velocity dispersion at different radii from the Galactic center. We interpret the radial profile of the line-of-sight velocity dispersion using a spherical Jeans equation under the assumptions of anisotropy/isotropy and that radial velocity dispersion is approximately equal to line-of-sight velocity dispersion . If we assume that the dark matter halo follows an NFW profile and the stellar halo is isotropic (β = 0), then can be directly used to estimate the virial mass of the Galactic dark matter halo, , and concentration parameter . In case that the stellar halo is anisotropic, we cannot avoid differentiation of sparse velocity dispersions according to the Jeans equation, which may cause overestimation of the mass. We use an isotropic case to test and find that overestimates the virial mass by 15% but within 1-σ error. We use to fit the NFW profile and get and in case of β = 0.3.