Trigonometric parallaxes of massive star-forming regions. VII. G9.62+0.20 and the expanding 3 kpc ARM

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+0.6-0.6 kpc. With an LSR velocity of about 2 km s-1, 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-1 radially outward from the Galactic center and 60 km s-1 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. © 2009. The American Astronomical Society. All rights reserved..