A highly-collimated SiO jet in the HH212 protostellar outflow

We mapped the inner 40 ′′ of the HH212 Class 0 outflow in SiO(2–1), SiO(5–4) and continuum using the Plateau de Bure interferometer in its extended configurations. The unprecedented angular resolution (down to 0. 34) allows accurate comparison with a new, deep H2 image obtained at the VLT. The SiO emission is confined to a highly-collimated bipolar jet (width ∼ 0. 35) along the outflow axis. The jet can be traced down to within 500 AU of the protostar, in a region that is heavily obscured in H2 images. Where both species are detected, SiO shows the same overall kinematics and structure as H2, indicating that both molecules are tracing the same material. We find that the high-velocity SiO gas is not tracing a wide-angle wind but is already confined to a flow inside a narrow cone of half-opening angle <6 at ≤ 500 AU from the protostar. Transverse cuts reveal no velocity gradient compatible with jet rotation above 1 km s, in contrast to previous claims based on H2 spectra. Subject headings: Stars: formation – Radio lines: ISM – ISM: jets and outflows – ISM: molecules – ISM: individual objects: HH212