Detection of Polarized CO Emission from the Molecular Outflow in NGC 1333 IRAS 4A

We report the first interferometric detection and mapping of linearly polarized spectral line emission due to the Goldreich-Kylafis effect. Our polarization maps of the CO J=2-->1 line in the molecular outflow powered by the very young stellar system NGC 1333 IRAS 4A make it possible to define the direction of the magnetic field in the outflow. Comparison with theoretical predictions implies that the magnetic field is parallel to the polarization. Our data suggest that the deflection of the outflow may be the result of the interaction between the outflow and the magnetic field. We also detect and map the linearly polarized dust continuum emission at 1.3 mm. The polarization map of the dust continuum is roughly consistent with an hourglass magnetic field morphology; i.e., it is in agreement with theoretical models of interstellar cloud contraction with a frozen-in magnetic field. The two techniques for mapping magnetic field morphologies agree. In general, the two techniques sample different column densities, and together they allow the study of magnetic field morphology over wider areas than either technique by itself would permit.