Oral Presentation

HELICAL MAGNETIC FIELDS IN THE NGC 1333 IRAS 4A PROTOSTELLAR OUTFLOWS

Author(s): Tao-Chung Chung (NAOC), Shih-Ping Lai (NTHU), Qizhou Zhang (CfA), Di Li (NAOC), Josep M. Girart (CSIC-IEEC), Ramprasad Rao (ASIAA), Zhi-Yun Li (U. of Virginia), Chin-Fei Lee (ASIAA), and Ian Stephens (CfA)

Presenter: Tao-Chung Ching (National Astronomical Observatories, Chinese Academy of Sciences (NAOC))

We present first ALMA CO 2-1 polarization observations and SMA CO 3-2 polarization observations toward NGC 1333 IRAS 4A. The CO Stokes I maps at an angular resolution of 0.3" reveal two bipolar outflows from the binary sources of NGC 1333 IRAS 4A. Close to the protostars, the CO polarization has a position angle approximately parallel to the magnetic field direction inferred from the dust polarizations. The CO polarization direction appears to vary smoothly from an hourglass field around the core to an arc-like morphology wrapping around the outflow, suggesting a helical structure of magnetic fields in the outflows. The helical magnetic field is consistent with the theoretical expectations for launching and collimating outflows from a magnetized rotating disk. The CO data reveal a PA of ∼30° deflection in the outflows. The variation in the CO polarization angle seems to correlate with the deflections. We speculate that the helical magnetic field contributes to ∼10° deflection of the outflows by means of Lorentz force.