Trigonometric Parallaxes of Massive Star Forming Regions: V. G23.01-0.41 and G23.44-0.18

TL;DR

This study measures precise distances and motions of two massive star-forming regions in the Milky Way, revealing their locations in spiral arms and significant deviations from circular orbits likely caused by gravitational effects of the Galactic bar.

Contribution

First trigonometric parallax measurements for G23.01-0.41 and G23.44-0.18, refining their distances and Galactic positions, and analyzing their peculiar motions.

Findings

G23.01-0.41 is closer than its kinematic distance, located in the Crux-Scutum arm.

G23.44-0.18 is near its near kinematic distance, in the Norma arm.

Both regions exhibit large peculiar motions of 20-30 km/s, possibly due to the Galactic bar.

Abstract

We report trigonometric parallaxes for the massive star-forming regions G23.01-0.41 and G23.44-0.18, corresponding to distances of 4.59 [+0.38/-0.33] kpc and 5.88 [+1.37/-0.93] kpc, respectively. The distance to G23.01-0.41 is smaller than its near kinematic distance assuming a standard model of the Milky Way and less than half of its far kinematic distance, which has usually been assumed. This places it in the Crux-Scutum spiral arm. The distance to G23.44-0.18 is close to its near kinematic distance and most likely places it in the Norma spiral arm near the end of the Galactic bar. Combining the distance and proper motions with observed radial velocities gives the location and full space motion of the star forming regions. We find large deviations from circular Galactic orbits for these sources: both sources show peculiar motions of 20 to 30 km/s counter to Galactic rotation and toward the Galactic center. These large peculiar motions might be the result of gravitational perturbations from the Galactic bar.