Submillimeter emission from the hot molecular jet HH 211

We observed the HH 211 jet in the submillimeter continuum and the CO (3-2) and SiO (8-7) transitions with the Submillimeter Array. The continuum source detected at the center of the outflow shows an elongated morphology, perpendicular to the direction of the outflow axis. The high-velocity emission of both molecules shows a knotty and highly collimated structure. The SiO (8-7) emission at the base of the outflow, close to the driving source, spans a wide range of velocities, from -20 up to 40 km s^-1. This suggests that a wide-angle wind may be the driving mechanism of the HH 211 outflow. For distances ≥5″ (∼1500 AU) from the driving source, emission from both transitions follows a Hubble-law behavior, with SiO (8-7) reaching higher velocities than CO (3-2) and being located upstream of the CO (3-2) knots. This indicates that the SiO (8-7) emission is likely tracing entrained gas very close to the primary jet, while the CO (3-2) is tracing less dense entrained gas. From the SiO (5-4) data of Hirano et al., we find that the SiO (8-7)/SiO (5-4) brightness temperature ratio along the jet decreases for knots far from the driving source. This is consistent with the density decreasing along the jet, from (3-10) × 10⁶ cm^-3 at 500 AU to (0.8-4) × 106 cm^-3 at 5000 AU from the driving source.