  The observational expectation of polarization measurements of thermal dust
radiation is investigated to find information on molecular outflows based on
magnetohydrodynamical (MHD) and radiation transfer simulations. There are two
major proposed models for the driving of molecular outflows: (1) molecular gas
is accelerated by a magnetic pressure gradient or magnetocentrifugal wind
mechanism before the magnetic field and molecular gas are decoupled, (2) the
linear momentum of a highly collimated jet is transferred to the ambient
molecular gas. In order to distinguish between these two models, it is crucial
to observe the configuration of the magnetic field. An observation of a
toroidal magnetic field is strong evidence that the first of the models is
appropriate. In this paper, we calculated the polarization distribution of
thermal dust radiation due to the alignment of dust grains along the magnetic
field using molecular outflow data calculated by two-dimensional axisymmetric
MHD simulations. An asymmetric distribution around the z-axis is characteristic
for magnetic fields composed of both poloidal and toroidal components. We
determined that the outflow has a low polarization degree compared with the
envelope and that the envelope and outflow have different polarization
directions (B-vector), namely, the magnetic field within the envelope is
parallel to the global magnetic field lines while the magnetic field of the
outflow is perpendicular to it. Thus we have demonstrated that the
point-symmetric (rather than axisymmetric) distributions of low polarization
regions indicate that molecular outflows are likely to be magnetically driven.
Observations of this polarization distribution with tools such as ALMA would
confirm the origin of the molecular outflow.
