Dust Polarization Toward Embedded Protostars in Ophiuchus with ALMA. II.
  IRAS 16293-2422
  We present high-resolution (~ 35 au) ALMA Band 6 1.3 mm dust polarization
observations of IRAS 16293. These observations spatially resolve the dust
polarization across the two protostellar sources and toward the filamentary
structures between them. The dust polarization and inferred magnetic field have
complicated structures throughout the region. In particular, we find that the
magnetic field is aligned parallel to three filamentary structures. We
characterize the physical properties of the filamentary structure that bridges
IRAS 16293A and IRAS 16293B and estimate a magnetic field strength of 23-78 mG
using the Davis-Chandrasekhar-Fermi method. We construct a toy model for the
bridge material assuming that the young stars dominate the mass and
gravitational potential of the system. We find that the expected gas flow to
each star is of comparable order to the Alfven speed, which suggests that the
field may be regulating the gas flow. We also find that the bridging material
should be depleted in ~ 1000 yr. If the bridge is part of the natal filament
that formed the stars, then it must have accreted new material. Alternatively,
the bridge could be a transient structure. Finally, we show that the 1.3 mm
polarization morphology of the optically thick IRAS 16293B system is
qualitatively similar to dust self-scattering. Based on similar polarization
measurements at 6.9 mm, we propose that IRAS 16293B has produced a substantial
population of large dust grains with sizes between 200 and 2000 um.
