  We have conducted ALMA cycle 2 observations in the 1.3 mm continuum and in
the C18O (2-1) and SO (5_6-4_5) lines at a resolution of ~0.3" toward the Class
0 protostar B335. The 1.3 mm continuum, C18O, and SO emission all show central
compact components with sizes of ~40-180 AU within more extended components.
The C18O component shows signs of infalling and rotational motion. By fitting
simple kinematic models to the C18O data, the protostellar mass is estimated to
be 0.05 Msun. The specific angular momentum, on a 100 AU scale, is ~4.3E-5
km/s*pc. A similar specific angular momentum, ~3E-5 to 5E-5 km/s*pc, is
measured on a 10 AU scale from the velocity gradient observed in the central SO
component, and there is no clear sign of an infalling motion in the SO
emission. By comparing the infalling and rotational motion, our ALMA results
suggest that the observed rotational motion has not yet reached Keplerian
velocity neither on a 100 AU nor even on a 10 AU scale. Consequently, the
radius of the Keplerian disk in B335 (if present) is expected to be 1-3 AU. The
expected disk radius in B335 is one to two orders of magnitude smaller than
those of observed Keplerian disks around other Class 0 protostars. Based on the
observed infalling and rotational motion from 0.1 pc to inner 100 AU scales,
there are two possible scenarios to explain the presence of such a small
Keplerian disk in B335: magnetic braking and young age. If our finding is the
consequence of magnetic braking, ~50% of the angular momentum of the infalling
material within a 1000 AU scale might have been removed, and the magnetic field
strength on a 1000 AU scale is estimated to be ~200 uG. If it is young age, the
infalling radius in B335 is estimated to be ~2700 AU, corresponding to a
collapsing time scale of ~5E4 yr.

Solar and Stellar Astrophysics;Astrophysics of Galaxies