Alignment of Outflows with Magnetic Fields in Cloud Cores

Abstract

We estimate the polarized thermal dust emission from MHD simulations of protostellar collapse and outflow formation in order to investigate the alignment of outflows with magnetic fields. The polarization maps indicate that the alignment of an outflow with the magnetic field depends on the field strength inside the cloud core; the direction of the outflow, projected on the plane of the sky, is aligned preferentially with the mean polarization vector for a cloud core with a magnetic field strength of 80 μG, while it does not tend to be aligned for 50 μG as long as the 1000 AU scale is considered. The direction of the magnetic field at the cloud center is probed by the direction of the outflow. In addition, the magnetic field at the cloud center can be revealed by the Atacama Large Millimeter Array (ALMA) even when the source is embedded deeply in the envelope. The Chandrasekhar-Fermi formula is examined using the polarization maps, indicating that the field strength predicted by the formula should be corrected by a factor of 0.24-0.44. The correction factor has a tendency to be lower for a cloud core with a weaker magnetic field.