ALMA Results of the Pseudodisk, Rotating disk, and Jet in Continuum and
  HCO+ in the Protostellar System HH 212
  HH 212 is a nearby (400 pc) Class 0 protostellar system showing several
components that can be compared with theoretical models of core collapse. We
have mapped it in 350 GHz continuum and HCO+ J=4-3 emission with ALMA at up to
~ 0.4" resolution. A flattened envelope and a compact disk are seen in
continuum around the central source, as seen before. The HCO+ kinematics shows
that the flattened envelope is infalling with small rotation (i.e., spiraling)
into the central source, and thus can be identified as a pseudodisk in the
models of magnetized core collapse. Also, the HCO+ kinematics shows that the
disk is rotating and can be rotationally supported. In addition, to account for
the missing HCO+ emission at low-redshifted velocity, an extended infalling
envelope is required, with its material flowing roughly parallel to the jet
axis toward the pseudodisk. This is expected if it is magnetized with an
hourglass B-field morphology. We have modeled the continuum and HCO+ emission
of the flattened envelope and disk simultaneously. We find that a jump in
density is required across the interface between the pseudodisk and the disk. A
jet is seen in HCO+ extending out to ~ 500 AU away from the central source,
with the peaks upstream of those seen before in SiO. The broad velocity range
and high HCO+ abundance indicate that the HCO+ emission traces internal shocks
in the jet.
