The ALMA view of the protostellar system HH212 - The wind, the cavity, and the disk

摘要

Context. Because it is viewed simply edge-on, the HH212 protostellar system is an ideal laboratory for studying the interplay of infall, outflow, and rotation in the earliest stages of low-mass star formation. Aims. We wish to exploit the unmatched combination of high angular resolution, high sensitivity, high-imaging fidelity, and spectral coverage provided by ALMA to shed light on the complex kinematics of the innermost central regions of HH212. Methods. We mapped the inner 10″ (4500 AU) of the HH212 system at ?0.5″ resolution in several molecular tracers and in the 850 μm dust continuum using the ALMA interferometer in band 7 in the extended configuration of the Early Science Cycle 0 operations. Results. Within a single ALMA spectral set-up, we simultaneously identify all the crucial ingredients known to be involved in the star formation recipe: (i) the fast, collimated bipolar SiO jet driven by the protostar; (ii) the large-scale swept-up CO outflow; (iii) the flattened rotating and infalling envelope, with bipolar cavities carved by the outflow (in C17O(3–2)); and (iv) a rotating wide-angle flow that fills the cavities and surrounds the axial jet (in C34S(7–6)). In addition, the compact high-velocity C17O emission (±1.9?3.5 km?s-1 from systemic) shows a velocity gradient along the equatorial plane consistent with a rotating disk of ? AU around a ?0.3 ± 0.1 M⊙ source. The rotating disk is possibly Keplerian. Conclusions. HH212 is the third Class 0 protostar with possible signatures of a Keplerian disk of radius ≥30 AU. The warped geometry in our CS data suggests that this large Keplerian disk might result from misaligned magnetic and rotation axes during the collapse phase. The wide-angle CS flow suggests that disk winds may be present in this source.