The outer rotation curve project with VERA: Trigonometric parallax of IRAS 05168+3634

TL;DR

This study uses VERA to measure the parallax of IRAS 05168+3634, revealing it is closer than previously thought and located in the Perseus arm, leading to revised Galactic parameters and insights into Galactic rotation dynamics.

Contribution

First precise trigonometric parallax measurement of IRAS 05168+3634, revising its distance and Galactic location, and analyzing its motion to understand Galactic rotation in the Perseus arm.

Findings

IRAS 05168+3634 is at 1.88 kpc, closer than the previous 6 kpc estimate.

Sources in the Perseus arm rotate more slowly than the Galactic rotation velocity.

Perseus arm sources exhibit systematic motions toward the Galactic Center and lag behind Galactic rotation.

Abstract

We present a measurement of the 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 is significantly closer than the previous distance estimate of 6 kpc based on a kinematic distance measurement. This drastic change in the source distance implies the need for revised values of not only the physical parameters of IRAS 05168+3634, but it also implies a different location in the Galaxy, placing it in the Perseus arm rather than the Outer arm. We also measured the proper motion of the source. A combination of the distance and proper motion with the systemic velocity yields a rotation velocity {\Theta} = 227 +9/-11 km s^-1 at the source position, 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 more slowly than the Galactic rotation velocity at the local standard of rest. In fact, we derive peculiar motions in the disk averaged over the seven sources in the Perseus arm of (U_mean, V_mean) = (11 +/- 3, -17 +/- 3) km s^-1, which indicates that these seven sources are moving systematically toward the Galactic Center and lag behind the overall Galactic rotation.