Protostellar disk formation and transport of angular momentum during
  magnetized core collapse
  Theoretical studies of collapsing clouds have found that even a relatively
weak magnetic field (B) may prevent the formation of disks and their
fragmentation. However, most previous studies have been limited to cases where
B and the rotation axis of the cloud are aligned. We study the transport of
angular momentum, and its effects on disk formation, for non-aligned initial
configurations and a range magnetic intensities. We perform 3D AMR MHD
simulations of magnetically supercritical collapsing dense cores using the code
Ramses. We compute the contributions of the processes transporting angular
momentum (J), in the envelope and the region of the disk. We clearly define
what could be defined as centrifugally supported disks and study their
properties. At variance with earlier analyses, we show that the transport of J
acts less efficiently in collapsing cores with non-aligned rotation axis and B.
Analytically, this result can be understood by taking into account the bending
of field lines occurring during the gravitational collapse. For the transport
of J, we conclude that magnetic braking in the mean direction of B tends to
dominate over both the gravitational and outflow transport of J. We find that
massive disks, containing at least 10% of the initial core mass, can form
during the earliest stages of star formation even for mass-to-flux ratios as
small as 3 to 5 times the critical value. At higher field intensities, the
early formation of massive disks is prevented. Given the ubiquity of Class I
disks, and because the early formation of massive disks can take place at
moderate magnetic intensities, we speculate that for stronger fields, disks
will form later, when most of the envelope will have been accreted. In
addition, we speculate that some observed early massive disks may actually be
outflow cavities, mistaken for disks by projection effects. (Abridged version
of the abstract.)
