The Density Profile and Kinematics of the Milky Way with RR Lyrae Stars

Abstract

Most of known RR Lyraes are type ab RR Lyraes (RRLab), and they are the excellent tool to map the Milky Way and its substructures. We find that 1148 RRLab stars determined by Drake et al.(2013) have been observed by spectroscopic surveys of SDSS and LAMOST. We derived radial velocity dispersion, circular velocity and mass profile from 860 halo tracers in our paper I. Here, we present the stellar densities and radial velocity distributions of thick disk and halo of the Milky Way. The 288 RRLab stars located in the thick disk have the mean metallicity of [Fe/H]$=-1.02$. Three thick disk tracers have the radial velocity lower than 215 km ${\mathrm{s}}^{-1}$. With 860 halo tracers which have a mean metallicity of [Fe/H]$=-1.33$, we find a double power-law of $n(r)\propto r^{-2.8}$ and $n(r)\propto r^{-4.8}$ with a break distance of 21 kpc to express the halo stellar density profile. The radial velocity dispersion at 50 kpc is around 78 km ${\mathrm{s}}^{-1}$.

arXiv comment12pages, 4 figures; accepted by ApJ

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