Accurate Distances of Massive Young Stars in the Scutum Spiral Arm

Abstract

As part of the BeSSeL Survey, we have used the Very Long Baseline Array to measure 16 trigonometric parallaxes and proper motions of molecular masers associated with 14 high-mass star-forming regions in the Scutum arm in the first quadrant of the Milky Way. This increases the number of maser sources with accurate distances in this arm to 42. The Scutum arm can now be traced over a length of ≈8 kpc and spanning ≈100° of Galactic azimuth. We find that the large inward peculiar motions noted by Immer et al. are concentrated near the end of the Galactic bar, while away from the bar modest peculiar motions more typical of spiral arms are seen, strengthening the suggestion that the large motions are induced by the bar.