Distance to NGC 281 in a Galactic Fragmenting Superbubble: Parallax Measurements with VERA

TL;DR

This study used VERA VLBI observations to measure the distance and proper motions of NGC 281, clarifying its position in the Galaxy and revealing the structure and expansion dynamics of its associated superbubble.

Contribution

First direct parallax measurement of NGC 281, resolving previous distance discrepancies and elucidating the superbubble's 3D structure and expansion within the Galactic disk.

Findings

Distance to NGC 281 is 2.82 kpc with high precision.

Superbubble size is approximately 650 pc and expanding at ~20 km/s.

Expansion is confined to the Galactic disk, not vertical.

Abstract

We have used the Japanese VLBI array VERA to perform high-precision astrometry of an H2O maser source in the Galactic star-forming region NGC 281 West, which has been considered to be part of a 300-pc superbubble. We successfully detected a trigonometric parallax of 0.355+/-0.030 mas, corresponding to a source distance of 2.82+/-0.24 kpc. Our direct distance determination of NGC 281 has resolved the large distance discrepancy between previous photometric and kinematic studies; likely NGC 281 is in the far side of the Perseus spiral arm. The source distance as well as the absolute proper motions were used to demonstrate the 3D structure and expansion of the NGC 281 superbubble, ~650 pc in size parallel to the Galactic disk and with a shape slightly elongated along the disk or spherical, but not vertically elongated, indicating the superbubble expansion may be confined to the disk. We estimate the expansion velocity of the superbubble as ~20 km/s both perpendicular to and parallel to the Galactic disk with a consistent timescale of ~20 Myr.