ALMA Dust Polarization Observations of Two Young Edge-on Protostellar
  Disks
  Polarized emission is detected in two young nearly edge-on protostellar disks
in 343 GHz continuum at ~ 50 au (~ 0.12") resolution with Atacama Large
Millimeter/submillimeter Array. One disk is in HH 212 (Class 0) and the other
in HH 111 (early Class I) protostellar system. Polarization fraction is ~ 1%.
The disk in HH 212 has a radius of ~ 60 au. The emission is mainly detected
from the nearside of the disk. The polarization orientations are almost
perpendicular to the disk major axis, consistent with either self-scattering or
emission by grains aligned with a poloidal field around the outer edge of the
disk because of optical depth effect and temperature gradient; the presence of
a poloidal field would facilitate the launching of a disk wind, for which there
is already tentative evidence in the same source. The disk of HH 111 VLA 1 has
a larger radius of ~ 220 au and is thus more resolved. The polarization
orientations are almost perpendicular to the disk major axis in the nearside,
but more along the major axis in the farside, forming roughly half of an
elliptical pattern there. It appears that toroidal and poloidal magnetic field
may explain the polarization on the near and far side of the disk,
respectively. However, it is also possible that the polarization is due to
self-scattering. In addition, alignment of dust grains by radiation flux may
play a role in the farside. Our observations reveal a diversity of disk
polarization patterns that should be taken into account in future modeling
efforts.
