Highly Ordered and Pinched Magnetic Fields in the Class 0 Proto-Binary
  System L1448 IRS 2
  We have carried out polarimetric observations with the Atacama Large
Millimeter/submillimeter Array (ALMA) toward the Class 0 protostellar system
L1448 IRS 2, which is a proto-binary embedded within a flattened, rotating
structure, and for which a hint of a central disk has been suggested, but whose
magnetic fields are aligned with the bipolar outflow on the cloud core scale.
Our high sensitivity and high resolution ($\sim 100$ au) observations show a
clear hourglass magnetic field morphology centered on the protostellar system,
but the central pattern is consistent with a toroidal field indicative of a
circumstellar disk, although other interpretations are also possible, including
field lines dragged by an equatorial accretion flow into a configuration
parallel to the midplane. If a relatively large disk does exist, it would
suggest that the magnetic braking catastrophe is averted in this system, not
through a large misalignment between the magnetic and rotation axes, but rather
through some other mechanisms, such as non-ideal magneto-hydrodynamic effects
and/or turbulence. We have also found a relationship of decreasing polarization
fractions with intensities and the various slopes of this relationship can be
understood as multiple polarization mechanisms and/or depolarization from a
changing field morphology. In addition, we found a prominent clumpy
depolarization strip crossing the center perpendicular to the bipolar outflow.
Moreover, a rough estimate of the magnetic field strength indicates that the
field is strong enough to hinder formation of a rotationally supported disk,
which is inconsistent with the feature of a central toroidal field.
