The Outer Galactic Halo As Probed By RR Lyr Stars From the Palomar Transient Facility + Keck

TL;DR

This study uses RR Lyrae stars from the Palomar Transient Facility and Keck observations to probe the Milky Way's outer halo, estimating its mass and analyzing stellar velocities at large distances.

Contribution

It provides new spectroscopic data on RR Lyrae stars in the Milky Way's outer halo, offering initial mass estimates and velocity distributions beyond 50 kpc.

Findings

Radial velocities of RR Lyrae stars between 50-110 kpc are measured.

Estimated Milky Way mass within 110 kpc is approximately 7 x 10^11 solar masses.

Data suggests a low total mass for the Milky Way's outer halo.

Abstract

We present initial results from our study of the outer halo of the Milky Way using a large sample of RR Lyr(ab) variables datamined from the archives of the Palomar Transient Facility. Of the 464 RR Lyr in our sample with distances exceeding 50 kpc, 62 have been observed spectroscopically at the Keck Observatory. Radial velocities and sigma(vr) are given as a function of distance between 50 and 110 kpc, and a very preliminary rather low total mass for the Milky Way out to 110 kpc of ~7 (+-1.5) x 10**11 solar masses is derived from our data.