ASTROMETRY AND SPATIO-KINEMATICS OF H2O MASERS IN THE MASSIVE STAR-FORMING REGION NGC 6334I(NORTH) WITH VERA

Abstract

We measured the trigonometric parallax of an H2O maser source associated with the massive star-forming region NGC 6334I(North), hereafter as NGC 6334I(N), with the VLBI Exploration of Radio Astrometry. The derived annual parallax is 0.789 ± 0.161 mas, corresponding to a distance of 1.26 kpc. Using the new distance, we recalculated the physical parameters (masses and luminosities) of the dust continuum cores in the region, and the revised parameters are only ~50% of their originally reported values. We also traced 23 relative proper motions of the H2O masers associated with SMA1 (central millimeter source in the region) between epochs, which exhibit an average amplitude of maser proper motion of ~2.03 mas yr–1 (~12.22 km s–1), tracing a bipolar outflow. The bipolar outflow structure extends through ~600 mas (~720 AU), with a dynamical timescale of ~295 yr. Using an expanding flow model, we derived the most plausible dynamical center of the outflow, pointing to SMA1b (1.3 cm and 7 mm continuum source) as the outflow driving source. Based on our results and other existing parallax results, we derive the pitch angles of the Sagittarius arm as 62 ± 54 along the Galactic longitude range of ~07 – ~401 assuming a perfect logarithmic spiral. We derived the peculiar motion of NGC 6334I(N) to be –4 ± 1 km s–1 toward the Galactic center, 8 ± 2 km s–1 in the direction of the Galactic rotation, and 25 ± 2 km s–1 toward the Galactic north pole.