Parallaxes of Star Forming Regions in the Outer Spiral Arm of the Milky Way

TL;DR

This study measures parallaxes and proper motions of star-forming regions in the Milky Way's Outer Spiral Arm, revealing its structure, motion, and warp characteristics using VLBA observations, and doubling existing data in the literature.

Contribution

It provides new parallax and proper motion measurements for three regions, significantly expanding the data on the Outer Spiral Arm and refining its structural and kinematic properties.

Findings

Outer Arm has a pitch angle of 14.9 +/- 2.7 degrees.

Galactocentric distance of the Outer Arm is 14.1 +/- 0.6 kpc.

No significant fall in the rotation curve out to 15 kpc.

Abstract

We report parallaxes and proper motions of three water maser sources in high-mass star-forming regions in the Outer Spiral Arm of the Milky Way. The observations were conducted with the Very Long Baseline Array as part of Bar and Spiral Structure Legacy Survey and double the number of such measurements in the literature. The Outer Arm has a pitch angle of 14.9 +/- 2.7 deg and a Galactocentric distance of 14.1 +/- 0.6 kpc toward the Galactic anticenter. The average motion of these sources toward the Galactic center is 10.7 +/- 2.1 km/s and we see no sign of a significant fall in the rotation curve out to 15 kpc from the Galactic center. The three-dimensional locations of these star-forming regions are consistent with a Galactic warp of several hundred parsecs from the plane.