Measurement of a Rotation Velocity of the Outer Galaxy with VERA: Mass Distribution of the Galaxy

摘要

We report measurement of trigonometric parallax of IRAS 05168+3634 with VERA. The parallax is 0.532±0.053 mas, corresponding to a distance of 1.88±_(0.17)~(0.21) kpc. This result is significantly smaller than the previous distance estimate based on kinematic distance, being 6 kpc. This drastic change in the source distance revises location of the source, placing it in the Perseus arm rather than the Outer arm. We also measure the proper motions of the source. Combination of the distance and the proper motions with the systemic velocity yields rotation velocity (Θ) of 227±_(11)~9 km s~(-1) at the source (Θ_0=240 km s~(-1) assumed). This indicates that a part of the outer rotation at Galacto-centric distance of ～ 10 kpc is smaller than the galactic rotation at the LSR, which is consistent with previous VERA and VLBA results. The lower rotation velocity may be caused in inner edge of the Perseus arm where shock front predicted by the density-wave theory occurs.