A Precise Distance to IRAS 00420+5530 via H2O Maser Parallax with the VLBA

TL;DR

This study uses VLBA to measure the parallax of H2O masers in IRAS 00420+5530, providing a precise distance that challenges previous estimates and reveals complex Galactic motions.

Contribution

The paper presents the first direct parallax measurement of IRAS 00420+5530, significantly refining its distance and revealing non-circular Galactic motions.

Findings

Distance to IRAS 00420+5530 is 2.17 kpc, much closer than previous estimates.

The region exhibits non-circular, slow Galactic orbit motions.

The Perseus arm is closer and more dynamically complex than previously thought.

Abstract

We have used the VLBA to measure the annual parallax of the H2O masers in the star-forming region IRAS 00420+5530. This measurement yields a direct distance estimate of 2.17 +/- 0.05 kpc (<3%), which disagrees substantially with the standard kinematic distance estimate of ~4.6 kpc (according to the rotation curve of Brand and Blitz 1993), as well as most of the broad range of distances (1.7-7.7 kpc) used in various astrophysical analyses in the literature. The 3-dimensional space velocity of IRAS 00420+5530 at this new, more accurate distance implies a substantial non-circular and anomalously slow Galactic orbit, consistent with similar observations of W3(OH) (Xu et al., 2006; Hachisuka et al. 2006), as well as line-of-sight velocity residuals in the rotation curve analysis of Brand and Blitz (1993). The Perseus spiral arm of the Galaxy is thus more than a factor of two closer than previously presumed, and exhibits motions substantially at odds with axisymmetric models of the rotating Galaxy.