Estimating the Kinematic Parameters and the Distance-Scale Zero Point for the Thin-Disk, Thick-Disk, and Halo Population Tracers via 3D Velocity Data

TL;DR

This study uses statistical parallax to determine the distance scale and kinematic parameters of Galactic populations, confirming a flat rotation curve and providing refined estimates for key Galactic distances and the Hubble constant.

Contribution

It introduces a method to simultaneously estimate the distance-scale zero point and kinematic parameters for multiple Galactic tracers using 3D velocity data.

Findings

Estimated local circular velocity of 210+/-6 km/s.

Confirmed flat Galactic rotation curve beyond 5 kpc.

Derived a solar Galactocentric distance of 7.7+/-0.4 kpc.

Abstract

We use the method of statistical parallax to constrain the distance-scale zero points and analyze the kinematics of extensive samples of Galactic classical Cepheids, RR Lyrae type variables, and blue horizontal branch stars, which serve as standard candles/kinematic tracers of various Galactic populations. We obtain three consistent estimates for the local circular velocity based on the mean velocities of halo RR Lyrae variables, BHB stars, and Galactic rotation curve inferred from Cepheid data with an average value of 210+/-6 km/s, which is close to the average circular velocity in the 5-40 kpc interval of Galactocentric distances inferred from BHB star data (195+/-5 km/s), thereby providing further supporting evidence for the practically flat shape of the Galactic rotation curve beyond ~5 kpc from the center. The inferred distance-scale corrections imply a solar Galactocentric distance of 7.7+/-0.4 kpc, an LMC distance modulus of 18.42+/-0.06, and a Hubble constant of 73-85 km/s/Mpc.