The Milky Way's Circular Velocity Curve and Its Constraint on the Galactic Mass with RR Lyrae Stars

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 first 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) and by considering the pulsation of the RRLab stars in our sample, we can obtain a reliable and comparable stellar halo circular velocity curve. We follow two different prescriptions for the velocity anisotropy parameter β in the Jeans equation to study the circular velocity curve and mass profile. Additionally, we test two different solar peculiar motions in our calculation. The best result we obtained with the adopted solar peculiar motion 1 of ( U , V , W ) = (11.1, 12, 7.2) km s −1 is that the enclosed mass of the Milky Way within 50 kpc is (3.75 ± 1.33) × 10 11 M ⊙ based on β  = 0 and the circular velocity 180 ± 31.92 (km s −1 ) at 50 kpc. This result is consistent with dynamical model results, and it is also comparable to the results of previous similar works.