Parallaxes of 6.7-GHz Methanol Masers towards the G305.2 High-Mass Star Formation Region

TL;DR

This study measures the parallax and proper motion of methanol masers in the G305.2 star formation region, refining its distance and spiral arm placement, and providing detailed maser structure maps.

Contribution

It provides the first parallax measurements for these masers, improving the understanding of the Galactic structure and spiral arm pitch angle.

Findings

Distance to G305.2 is 4.1 kpc with uncertainties.

G305.2 is located in the Carina-Sagittarius spiral arm.

Masers exhibit simple linear and ring-like structures.

Abstract

We have made measurements to determine the parallax and proper motion of the three 6.7-GHz methanol masers G305.200$+$0.019, G305.202$+$0.208 and G305.208$+$0.206. The combined parallax is found to be 0.25$\pm $0.05 mas, corresponding to a distance of 4.1$^{+1.2}_{-0.7}$ kpc. This places the G305.2 star formation region in the Carina-Sagittarius spiral arm. The inclusion of G305.2 increases the Galactic azimuth range of the sources in this arm by 40$^\circ $ from Sato et al., allowing us to determine the pitch angle of this spiral with greater confidence to be $\psi = 19.0 \pm 2.6^\circ $. The first VLBI spot maps of the 6.7-GHz methanol masers towards these sources show that they have simple linear and ring-like structures, consistent with emission expected from classII methanol masers in general.