Trigonometric Parallaxes of Massive Star-Forming Regions: VII. G9.62+0.20 and the Expanding 3 KPC-ARM

TL;DR

This study measures the precise distance and motion of the star-forming region G9.62+0.20 using trigonometric parallax, revealing significant deviations from expected Galactic rotation and associating it with the inner Galaxy's dynamic structures.

Contribution

First direct parallax measurement of G9.62+0.20, providing accurate distance and motion data that challenge kinematic estimates and reveal complex Galactic dynamics.

Findings

Distance of 5.2±0.6 kpc from parallax measurement

Large peculiar motion deviating from circular orbit

Association with the inner 3 kpc-Arm near the Galactic bulge

Abstract

We report a trigonometric parallax of 12 GHz methanol masers associated with the massive star forming region G9.62+0.20, corresponding to a distance of 5.2+-0.6 kpc. With a local standard of rest velocity of about 2 km/s, the region's kinematic distances of 0.5 and 16 kpc differ greatly from the distance derived here. Our measurement of the peculiar motion of the star forming region shows a very large deviation from a circular Galactic orbit: 41 km/s radially outward from the Galactic center and 60 km/s counter to Galactic rotation. The combination of its radial velocity and distance places G9.62+0.20 in the inner region of the Galaxy close to the Expanding Near 3 kpc-Arm, where the bulge/bar potential has strong gravitational influence. We also map the distribution of 12 GHz methanol masers, locate them with respect to a hypercompact H II region, and compare our data with the periodic flare phenomenon reported previously for this source.