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

Abstract

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 about 0.5 arcsec resolution in several molecular tracers and in the 850 $\hat{I}¼$m 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 namely: (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 C${}^{17}$O(3--2)), and (iv) a rotating wide-angle flow that fills the cavities and surrounding the axial jet (in C${}^{34}$S(7--6)). In addition, the compact high-velocity C${}^{17}$O emission ($\pm$ 1.9--3.5 km s${}^{-1}$ from systemic) shows a velocity gradient along the equatorial plane consistent with a rotating disk of about 0.2 arcsec = 90 AU around a $\simeq 0.3\pm 0.1M_{\odot }$ source. The rotating disk is possibly Keplerian. Conclusions: HH212 is the third Class 0 protostar with possible signatures of a Keplerian disk of radius $\ge 30AU$. 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.

Astronomy & Astrophysics Letter, in press