Echelle spectroscopy of shocked H2 in the L1448 outflow

Here we investigate the dynamical properties of the outflow from a Class 0 protostar. We have observed H2 v=1-0 S(1) velocity profiles at eight slit positions in the northern lobe of the outflow driven by L 1448-mm (the VLA source L 1448C). Complex line profiles are observed throughout the region; the peak H2 emission is everywhere strongly blue-shifted. The velocities of the line profile peaks also gradually increase along the length of the outflow. This we attribute to the bending of the flow towards the observer. The flow produces numerous bow shocks along its length (as evidenced by the triangular H2 profiles) that are intersperced with a turbulent shear layer (resulting in the more Gaussian profiles). Knot A is a superb example of a bow shock. Its spatial distribution corresponds to a C-type bow, and this is confirmed by our velocity-position analysis: the profiles are wide and double-peaked just behind the bow apex. There is also evidence that all the H2 emission features are produced within an expanding wind of high Alfvèn speed. Analysis of the main "ridge" of emission suggests the presence of many small clumps, formed after the wind terminates at an oblique shock. We may therefore be witnessing the shredding and dispersal of the molecular cloud core by the L 1448-mm outflow.