The jet - driven molecular outflow of HH 211

We present high angular resolution (down to ∼ 1.5′′) interferometric maps of the CO J = 1→0 and J = 2→1 emission in the molecular outflow associated with the extremely young HH 211 jet, which is located in the IC 348 molecular complex. At velocities close to the systemic velocity, the CO emission traces the outflow cavities, while an extremely collimated, continuous jet-like structure is observed at high CO velocities. The continuum emission reveals a ∼ 0.2 M dust condensation surrounding the central exciting (Class 0) protostar, clearly resolved and elongated perpendicular to the jet axis. The strong (bow-)shocks observed in vibrationally excited H2 emission are located at the terminal ends of the jet and the low-velocity CO cavities are precisely situated in their wake. Hence, the overall structure of HH 211 perfectly fits into the picture of a jet-driven flow and strongly supports shock-entrainment models as the formation mechanisms of young, embedded molecular outflows. The shape of the cavities traced by the low-velocity CO emission can actually be (surprisingly well) reproduced by a simple, semi-analytical toy-model of a jet-driven flow, in which prompt entrainment occurs at the head of a travelling bow-shock. The estimated jet mass and mass loss rate yield a timescale of order one thousand years, in agreement with the kinematical age. Finally, we discuss the physical properties of the different parts of the outflow, and especially the actual nature of the high-velocity CO jet.