Trigonometric Parallaxes of Star Forming Regions in the Scutum Spiral Arm

TL;DR

This study measures the distances to star-forming regions in the Milky Way's Scutum arm using trigonometric parallaxes, revealing a larger pitch angle and specific peculiar motions, which enhance understanding of the Galaxy's spiral structure.

Contribution

The paper provides new parallax measurements for six regions and refines the spiral arm's pitch angle and kinematic properties, highlighting the arm's proximity to the Galactic bar.

Findings

Estimated pitch angle of 19.8 degrees for the Scutum arm.

Sources exhibit an average peculiar motion of 4 km/s slower than Galactic rotation.

Sources show an 8 km/s motion toward the Galactic center.

Abstract

We report measurements of trigonometric parallaxes for six high-mass star-forming regions in the Scutum spiral arm of the Milky Way as part of the BeSSeL Survey. Combining our measurements with 10 previous measurements from the BeSSeL Survey yields a total sample of 16 sources in the Scutum arm with trigonometric parallaxes in the Galactic longitude range from 5 deg to 32 deg. Assuming a logarithmic spiral model, we estimate a pitch angle of 19.8 (+/-3.1) deg for the Scutum arm, which is larger than pitch angles reported for other spiral arms. The high pitch angle of the arm may be due to the arm's proximity to the Galactic bar. The Scutum arm sources show an average peculiar motion of 4 km/s slower than the Galactic rotation and 8 km/s toward the Galactic center. While the direction of this non-circular motion has the same sign as determined for sources in other spiral arms, the motion toward the Galactic center is greater for the Scutum arm sources.