DG Tauri B: The interaction of an atomic jet with ambient molecular gas

We have made high-resolution (4 '') observations of the 2.6 mm continuum and CO (1-0) line emission associated with the young stellar object DG Tau B. The aperture-synthesis CO map clearly shows that redshifted emission is symmetrically distributed about the DG Tau B optical jet and extends at least 6000 AU to the northwest of the unresolved continuum source. By contrast, blueshifted CO emission is confirmed to a compact region, which is less than 500 AU in radius. Within 1000 AU of the star, the redshifted CO emission is elongated, brightest along its central axis, and unresolved in the transverse direction. Beyond 1000 AU, the flow broadens and begins to bifurcate. The morphology of the CO emission provides compelling evidence that the extended molecular outflow is driven by the highly collimated atomic jet. The spatial correspondence between knots in the optical jet and successive broadenings of the outflow supports the hypothesis that the molecular outflow is produced by the action of multiple working surfaces in a time-varying jet.