New discovery of CO(J=3-2) linear polarization by Goldreich-Kylafis effect from protostellar outflow in NGC 2071 IRS 3

ABSTRACT :
The linear polarized molecular line emission caused by the Goldreich-Kylafis effect has some potentials to reveal the morphology of the magnetic field in Position-Position-Velocity space, in spite of a 90-degree ambiguity between the orientation of the magnetic field and that of the linear polarization.
Polarization observations for several transitions of a molecular species are rare but crucial for comparing the theoretical expectation and accurately estimating the magnetic field.
Here we report new, clear, velocity-spatial-resolved CO(J=3-2) linear polarization toward the protostellar outflow in NGC 2071 IRS 3 with Atacama Large Millimeter/submillimeter Array (ALMA).
In the low-velocity redshifted outflow, we confirmed linear polarizations with a fraction of 0.7%, suggesting that higher transitions of CO can also produce reasonably detectable linear polarization due to the G-K effect in certain environments.
The polarization angle indicates that the low-velocity outflow has a helical magnetic field, consistent with recent magnetohydrodynamic simulations.
Since the polarization of CO(J=2-1) also had detected previously in same region, this system is suitable to disclose the magnetic field associated to the protostellar outflow with resolving arbitrariness.
In addition to the need for polarization observations of multiple transitions of CO and other species with ALMA, numerical calculations and subsequent synthetic model constructions for unobserved transitions and molecular species should be performed in the future.