Near-infrared imaging in H_2_ of molecular (CO) outflows from young stars.

In an attempt to identify the molecular shocks associated with the acceleration of ambient gas by collimated outflows from young stars, we have imaged a number of known molecular (CO) outflows in H_2_ v=1-0 S(1) and wide-band K. H_2_ line emission is detected in all six sources: (o) In the L 1157, VLA 1623 and NGC 6334I outflows, bow-shaped H_2_ features are observed coincident with or just ahead of (downwind of) peaks in the CO outflow maps. (o) In NGC 2264G, as well as a compact group of H_2_ knots coincident with the blue-shifted CO peak, we see an extended H_2_ filament that traces the northern edge of the red-shifted CO flow. (o) In the L 1641N and Haro 4-255 molecular outflows we see a close correlation between H_2_ line emission features and peaks in the CO outflow maps. In each outflow system, the H_2_ probably results from shocks associated with the interaction of the flow with the ambient, molecular gas. A comparison of the H_2_ data with CO outflow maps strongly suggests that "prompt entrainment" near the head of a jet is the dominant mechanism for producing the CO outflows in at least some of these sources. We are also able to account for the ratios of observed radiated energy (derived from H_2_ v=1-0 S(1) flux measurements) to mechanical power in the CO outflows in at least half of the outflows with a very simple, strong, radiative shock model.