Super-fast Rotation in the OMC 2/FIR 6b Jet
  We present ALMA CO ($J$=2--1) and 1.3 mm continuum observations of the
high-velocity jet associated with the FIR 6b protostar located in the Orion
Molecular Cloud-2. We detect a velocity gradient along the short axis of the
jet in both the red- and blue-shifted components. The position-velocity
diagrams along the short axis of the red-shifted jet show a typical
characteristic of a rotating cylinder. We attribute the velocity gradient in
the red-shifted component to rotation of the jet. The rotation velocity
($>20\,\ \rm{km s^{-1}}$) and specific angular momentum ($>10^{22}\,
\rm{cm^{2}\, s^{-1}}$) of the jet around FIR 6b are the largest among all jets
in which rotation has been observed. By combining disk wind theory with our
observations, the jet launching radius is estimated to be in the range of
$2.18-2.96$\,au. The rapid rotation, large specific angular momentum, and a
launching radius far from the central protostar can be explained by a
magnetohydrodynamic disk wind that contributes to the angular momentum transfer
in the late stages of protostellar accretion.
