Anomalous peculiar motions of high-mass young stars in the Scutum spiral arm

TL;DR

This study measures the motions of high-mass star-forming regions in the Scutum spiral arm, revealing significant peculiar velocities likely influenced by the Galaxy's spiral structure and bar.

Contribution

It provides a comprehensive set of parallax and proper motion data for 44 high-mass star-forming regions in the Scutum arm, highlighting their anomalous motions.

Findings

16 sources exhibit large peculiar motions

13 of these motions are directed toward the Galactic center

High peculiar motions are likely due to the combined gravitational effects of the spiral arm and Galactic bar

Abstract

We present trigonometric parallax and proper motion measurements toward 22 GHz water and 6.7 GHz methanol masers in 16 high-mass star-forming regions. These sources are all located in the Scutum spiral arm of the Milky Way. The observations were conducted as part of the Bar and Spiral Structure Legacy (BeSSeL) survey. A combination of 14 sources from a forthcoming study and 14 sources from the literature, we now have a sample of 44 sources in the Scutum spiral arm, covering a Galactic longitude range from 0$^\circ$ to 33$^\circ$. A group of 16 sources shows large peculiar motions of which 13 are oriented toward the inner Galaxy. A likely explanation for these high peculiar motions is the combined gravitational potential of the spiral arm and the Galactic bar.