Magnetically regulated collapse in the B335 protostar ? I. ALMA
  observations of the polarized dust emission
  The role of the magnetic field during protostellar collapse is poorly
constrained from an observational point of view, although it could be
significant if we believe state-of-the-art models of protostellar formation. We
present polarimetric observations of the 233 GHz thermal dust continuum
emission obtained with ALMA in the B335 Class 0 protostar. Linearly polarized
dust emission arising from the circumstellar material in the envelope of B335
is detected at all scales probed by our observations, from radii of 50 to 1000
au. The magnetic field structure producing the dust polarization has a very
ordered topology in the inner envelope, with a transition from a large-scale
poloidal magnetic field, in the outflow direction, to strongly pinched in the
equatorial direction. This is probably due to magnetic field lines being
dragged along the dominating infall direction since B335 does not exhibit
prominent rotation. Our data and their qualitative comparison to a family of
magnetized protostellar collapse models show that, during the magnetized
collapse in B335, the magnetic field is maintaining a high level of
organization from scales 1000 au to 50 au: this suggests the field is
dynamically relevant and capable of influencing the typical outcome of
protostellar collapse, such as regulating the disk size in B335.
