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




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 discs, outflows, shock fronts or discs 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 discs. To follow up this suggestion, we have determined magnetic field directions from full polarization 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 discs in three sources. 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.