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

TL;DR

This study uses RR Lyrae stars to map the Milky Way's structure, revealing detailed density profiles and kinematic properties of its thick disk and halo, based on spectroscopic data from SDSS and LAMOST.

Contribution

It provides new measurements of stellar densities and velocity distributions in the Milky Way's thick disk and halo using RR Lyrae stars, including a double power-law density profile.

Findings

Halo density follows a double power-law with a break at 21 kpc.

Radial velocity dispersion at 50 kpc is approximately 78 km/s.

Mean metallicity of thick disk RR Lyrae stars is -1.02.

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 $\rm s^{-1}$. 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 $\rm s^{-1}$.