Outer rotation curve of the Galaxy with VERA IV: Astrometry of IRAS 01123+6430 and the possibility of cloud-cloud collision

TL;DR

This study measures the distance and motion of a star-forming region in the Galaxy using VLBI, confirming a flat rotation curve and suggesting cloud-cloud collision as a star formation mechanism.

Contribution

First VLBI parallax measurement of IRAS 01123+6430 providing accurate distance and motion data, supporting flat Galactic rotation and cloud-cloud collision influence.

Findings

Galactic rotation curve is flat at the measured radius.

Distance to IRAS 01123+6430 is approximately 6.61 kpc.

Evidence of cloud-cloud collision with low relative velocity.

Abstract

As part our investigation into the Galactic rotation curve, we carried out Very Long Baseline Interferometry (VLBI) observations towards the star-forming region IRAS 01123+6430 using VLBI Exploration of Radio Astrometry (VERA) to measure its annual parallax and proper motion. The annual parallax was measured to be 0.151+/-0.042 mas, which corresponds to a distance of D=6.61^{+2.55}_{-1.44} kpc, and the obtained proper motion components were ({\mu}_{\alpha}cos{\delta}, {\mu}_{\delta})=(-1.44+/-0.15, -0.27+/-0.16) mas yr^{-1} in equatorial coordinates. Assuming Galactic constants of (R_0, {\Theta}_0)=(8.05+/-0.45 kpc, 238+/-14 km s^{-1}), the Galactocentric distance and rotation velocity were measured to be (R, {\Theta})=(13.04+/-2.24 kpc, 239+/-22 km s^{-1}), which are consistent with a flat Galactic rotation curve. The newly estimated distance provides a more accurate bolometric luminosity of the central young stellar object, L_Bol=(3.11+/-2.86)\times 10^3 L_solar, which corresponds to a spectral type of B1-B2. The analysis of 12CO(J=1-0) survey data obtained with the Five College Radio Astronomical Observatory (FCRAO) 14 m telescope shows that the molecular cloud associated with IRAS 01123+6430 consists of arc-like and linear components, which well matches a structure predicted by numerical simulation of the cloud-cloud collision (CCC) phenomenon. The coexistence of arc-like and linear components implies that the relative velocity of initial two clouds was as slow as 3-5 km s^{-1}, which meets the expected criteria of massive star formation where the core mass is effectively increased in the presence of low relative velocity (~3-5 km s^{-1}), as suggested by Takahira et al.(2014).