Outer Rotation Curve of the Galaxy with VERA I: Trigonometric parallax of IRAS 05168+3634

TL;DR

This study uses VERA to measure the trigonometric parallax of IRAS 05168+3634, revising its distance and location, and analyzing its motion to understand Galactic rotation and peculiar velocities in the Perseus arm.

Contribution

First direct parallax measurement of IRAS 05168+3634 with VERA, revising its distance and Galactic location, and analyzing its motion to inform Galactic rotation models.

Findings

Distance to IRAS 05168+3634 is approximately 1.88 kpc, much closer than previous estimates.

Sources in the Perseus arm rotate slower than the Galactic rotation velocity at the LSR.

Sources in the Perseus arm exhibit systematic peculiar motions toward the Galactic center and lagging behind Galactic rotation.

Abstract

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+0.21/-0.17 kpc. This result is significantly smaller than the previous distance estimate of 6 kpc based on kinematic distance. This drastic change in the source distance revises not only physical parameters of IRAS 05168+3634, but also its location of the source, placing it in the Perseus arm rather than the Outer arm. We also measure proper motions of the source. A combination of the distance and the proper motions with systemic velocity yields rotation velocity ({\Theta}) of 227+9/-11 km s-1 at the source, assuming {\Theta}0 = 240 km s-1. Our result combined with previous VLBI results for six sources in the Perseus arm indicates that the sources rotate systematically slower than the Galactic rotation velocity at the LSR. In fact, we show observed disk peculiar motions averaged over the seven sources in the Perseus arm as (Umean, Vmean) = (11 +/- 3, -17 +/- 3) km s-1, indicating that these seven sources are systematically moving toward the Galactic center, and lag behind the Galactic rotation.