Silicon Monoxide and Methanol Emission from the NGC 2071 Molecular Outflow

Abstract

We report observations of emission in the J = 3 → 2 and J = 2 → 1 transitions of SiO and Jk = 3k → 2k transitions of CH3OH, made with the Swedish-ESO Submillimeter Telescope (SEST), toward the high-velocity, collimated molecular outflow in NGC 2071. Emission is detected from the lobes, as well as from the central core region, in both species. The spatial distribution of the SiO wing emission, which is detected over a velocity range of ~50 km s-1, shows three distinct features: a blueshifted clump located toward the northeast, a redshifted clump located toward the southwest, and a central structure, with moderate redshifted velocities, located near the cluster of young stellar objects. The shape of the SiO profiles from the northeast and southwest clumps are distinctly different. The SiO lines from the northeast clump exhibit a peak near the velocity of the ambient cloud and a gradual decline toward blueshifted velocities reaching flow velocities of up to -32 km s-1. On the other hand, the SiO profiles from the southwest clump show a peak emission at a velocity that is redshifted by ~8.5 km s-1 from the ambient gas velocity and a gradual decline in brightness toward the ambient cloud velocity. We suggest that the SiO emission from the clumps are signposts of working surfaces where a collimated jet is interacting with ambient material, and ascribe the differences in line shape to differences in the density of the environment under which the jet is propagating. The abundance of silicon monoxide in the outflow lobes is found to be enhanced, with respect to that of quiescent ambient gas in dark globules, by at least 2 orders of magnitude (peak enhancement ≥500 in the southwest clump and ≥170 in the northeast clump). The abundance of methanol is considerably more enhanced in the southwest clump (peak enhancement of ~500) than in the northwest clump (peak enhancement of ~70). We suggest that the large enhancements of methanol and silicon monoxide in the outflow clumps are most likely due to the release from grains of ice mantles and Si-bearing species via shocks produced by the interaction between the outflow and dense ambient gas, and attribute the differences in enhancements to the different shock velocities attained in the northeast clump (vs ~ 45 km s-1) and southwest clump (vs ~ 12 km s-1).