ALMA High Angular Resolution Polarization Study; An Extremely Young
  Class 0 Source, OMC-3/MMS 6
  Using the $\approx$15km ALMA long baselines, we imaged the Stokes $I$
emission and linearly polarized intensity ($PI$) in the 1.1-mm continuum band
of a very young intermediate-mass protostellar source, MMS 6, in the Orion
Molecular Cloud-3. The achieved angular resolution, $0''.02{\times}0''.03$
($\approx$10 AU), shows for the first time a wealth of data on the dust
emission polarization in the central 200 AU of a protostar. The $PI$ peak is
offset to the south-west (SW) by $\approx$20 AU with respect to the Stokes $I$
peak. Its polarization degree is 11 % with its $E$-vector orientation of
P.A.${\approx}135^{\circ}$. A partial ring-like structure with a radius of
$\approx$80 AU is detected in $PI$ but not in the Stokes $I$. NW (north-west)
and SE (south-east) parts of the ring are bright with a high polarization
degree of $\gtrsim$10 %, and their $E$-vector orientations are roughly
orthogonal to those observed near the center. We also detected arm-like
polarized structures, extending to 1000 AU scale to the north, with the
$E$-vectors aligned along the minor axis of the structures. We explored
possible origins of the polarized emission comparing with magnetohydrodynamical
(MHD) simulations of the toroidal wrapping of the magnetic field. The
simulations are consistent with the $PI$ emission in the ring-like and the
extended arm-like structures observed with ALMA. However, the current
simulations do not completely reproduce observed polarization characteristics
in the central 50 AU. Although the self-scattering model can explain the
polarization pattern and positional offset between the Stokes $I$ and $PI$,
this model is not able to reproduce the observed high degree of polarization.
