ALMA RESULTS OF THE PSEUDODISK, ROTATING DISK, AND JET IN THE CONTINUUM AND HCO⁺IN THE PROTOSTELLAR SYSTEM HH 212

Abstract

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