First polarimetry results of two candidate high-mass protostellar objects

Abstract

We present 850micron imaging polarimetry of two high-mass star forming regions - W48 and S152. Within these regions we have identified two candidate high-mass protostellar objects - W48W and S152SE. The submillimetre continuum emission from the candidate HMPOs is bright in comparison to the nearby HII regions. W48W is a cold dense source, with no radio or mid-infrared emission. S152SE has an IRAS source IRAS 22566+5828 in the Southwestern part of the region, which appears in the mid-infrared 8.28micron emission, but there is no radio emission. The 850micron data shows another core within the region, in the Northeast. The polarimetry is ordered and the degree of polarisation is high over the candidate HMPOs - ~6% for W48W and ~8% for S152SE. Polarimetry results of this nature indicate a strong, ordered magnetic field threading the candidate HMPOs. The magnetic field direction in both S152SE and W48W is perpendicular to the direction of elongation of the cloud which would imply collapse along the field lines. Estimates of the magnetic field strength are derived using the Chandrasekhar & Fermi method. We calculate plane of the sky field strengths of ~0.7 mG for W48W and ~0.2 mG for S152SE. We discuss the drawbacks of using the Chandrasekhar & Fermi method with a large beam size. Mass-to-flux ratios have been calculated and both clouds are found to be roughly critical.