Probing the magnetic fields of massive star forming regions with methanol maser polarisation

TL;DR

This study uses methanol maser polarisation observations to investigate magnetic field structures in massive star-forming regions, revealing diverse morphologies that challenge existing models and suggest complex local environments.

Contribution

The paper provides the first polarisation-based magnetic field mapping of 10 methanol maser sources, highlighting the diversity of magnetic field orientations and questioning current star formation models.

Findings

Magnetic fields are aligned with source structures in some cases, indicating shocks or outflows.

In other cases, magnetic fields are perpendicular, suggesting disk-related environments.

Results show no consistent support for existing models, implying complex or varied star formation processes.

Abstract

Methanol masers can provide valuable insight into the processes involved in high-mass star formation, however the local environment in which they form is still unclear. Four primary, yet conflicting, models have emerged to explain the commonly observed methanol maser structures at 6.67 GHz. These suggest that masers trace accretion disks, outflows, shock fronts or disks dominated by infall/outflows. One proposed means of testing these models is through mapping the local magnetic field structures around maser sources, which were predicted to lie parallel to shock and outflows and perpendicular to accretion disks. To follow up this suggestion we have determined magnetic field directions from full polarisation observations of 10 6.67-GHz sources. We find morphology that is parallel to the source structure, indicative of shocks or outflows, in five sources and perpendicular morphology indicative of disks in three. These results do not support any of the expected models and the diverse morphologies observed indicate that the masers could be emitting from different evolutionary stages or environments, or from a common local environment with complex associated magnetic fields. To resolve this conflict we suggest a new approach that will search the simulations of massive star formation, which are just becoming available, for suitable sites for maser emission.