The Milky Way's circular velocity curve and its constraint on the Galactic mass with RR Lyrae stars

TL;DR

This study uses RR Lyrae stars to derive the Milky Way's circular velocity curve and mass profile within 50 kpc, providing constraints consistent with previous dynamical models and improving understanding of Galactic mass distribution.

Contribution

It presents a new analysis of the Galactic halo's circular velocity curve using a large sample of RR Lyrae stars with precise distances and velocities, incorporating different velocity anisotropy assumptions.

Findings

Milky Way mass within 50 kpc is approximately 3.75 x 10^11 solar masses.

Circular velocity at 50 kpc is about 180 km/s with a margin of error.

Results align with previous dynamical models and studies.

Abstract

We present a sample of 1148 ab-type RR Lyrae (RRLab) variables identified from Catalina Surveys Data Release 1, combined with SDSS DR8 and LAMOST DR4 spectral data. We firstly use a large sample of 860 Galactic halo RRLab stars and derive the circular velocity distributions for the stellar halo. With the precise distances and carefully determined radial velocities (the center-of-mass radial velocities) by considering the pulsation of the RRLab stars in our sample, we can obtain a reliable and comparable stellar halo circular velocity curve. We take two different prescriptions for the velocity anisotropy parameter {\beta} in the Jeans equation to study the circular velocity curve and mass profile. We test two different solar peculiar motions in our calculation. Our best result with the adopted solar peculiar motion 1 of (U, V, W) = (11.1, 12, 7.2) km/s is that the enclosed mass of the Milky Way within 50 kpc is (3.75 +/- 1.33) *10^11Msun based on \beta = 0 and the circular velocity 180 +/- 31.92 (km/s) at 50 kpc. This result is consistent with dynamical model results, and it is also comparable to the previous similar works.