MAGMO: Coherent magnetic fields in the star forming regions of the Carina-Sagittarius spiral arm tangent

TL;DR

This study uses hydroxyl masers to trace magnetic fields in star-forming regions of the Carina-Sagittarius spiral arm, revealing coherent magnetic field orientations over several kiloparsecs.

Contribution

First pilot project to measure magnetic fields via Zeeman splitting of masers in the Carina-Sagittarius spiral arm tangent, demonstrating the feasibility of mapping Galactic magnetic fields.

Findings

Detected hydroxyl masers in 11 of 23 sites, including 9 new detections.

Measured magnetic field strengths between -1.5 mG and +3.8 mG.

Found coherent magnetic field orientation across 5.3 kpc.

Abstract

We present the pilot results of the `MAGMO' project, targeted observations of ground-state hydroxyl masers towards sites of 6.7-GHz methanol maser emission in the Carina-Sagittarius spiral arm tangent, Galactic longitudes 280 degrees to 295 degrees. The `MAGMO' project aims to determine if Galactic magnetic fields can be traced with Zeeman splitting of masers associated with star formation. Pilot observations of 23 sites of methanol maser emission were made, with the detection of ground-state hydroxyl masers towards 11 of these and six additional offset sites. Of these 17 sites, nine are new detections of sites of 1665-MHz maser emission, three of them accompanied by 1667-MHz emission. More than 70% of the maser features have significant circular polarization, whilst only ~10% have significant linear polarization (although some features with up to 100% linear polarization are found). We find 11 Zeeman pairs across six sites of high-mass star formation with implied magnetic field strengths between -1.5 mG and +3.8 mG and a median field strength of +1.6 mG. Our measurements of Zeeman splitting imply that a coherent field orientation is experienced by the maser sites across a distance of 5.3+/-2.0 kpc within the Carina-Sagittarius spiral arm tangent.