Submillimeter Polarimetry of Class 0 Protostars: Constraints on Magnetized Outflow Models

Abstract

Polarized 800 μm emission from magnetically aligned dust grains has been detected in five protostars. Previously, only two such detections had been made. All of these protostellar sources have associated bipolar outflows and presumably also circumstellar disks. We find that the angle between the deduced magnetic field direction and the outflow axis, Δθ, appears to be correlated with the angle between the line of sight to the observer and the outflow direction, θlos. If the outflow is in the plane of the sky, then the deduced magnetic field tends to be perpendicular to the outflow, and if the outflow is angled toward the observer, then the magnetic field tends to lie parallel to the outflow. Various magnetic field geometries could explain this trend. In addition, the 800 μm percentage polarization, p, appears to be inversely correlated with the ratio of Lbol/L1.3 mm, which is a measure of the evolutionary stage of the source, and with the bipolar outflow opening angle, which also increases as a source evolves, and it appears to be correlated with source distance. We interpret these results as indicating that the observed magnetic field is more ordered in younger sources. The most likely interpretation of the distance correlation appears to be that the field is more ordered in more massive sources. As yet, there are no theoretical models for the magnetic fields around protostars that can fully explain all of these correlations.