Jet driven molecular outflows in Orion

Abstract

We present high sensitivity and high angular resolution images of the high velocity (vLSR>30kms^-1) CO emission in the J=1-0 and J=2-1 lines of the Orion KL region. These results reveal the morphology of the high-velocity CO emission at the most extreme velocities. High velocity emission have been only detected in two regions: BN/KL (IRc2/I) and Orion-S. The Orion-S region contains a very young (dynamical age of 10^3years), very fast (~110kms^-1) and very compact (<0.16pc) bipolar outflow. From the morphology of the high-velocity gas we estimate that the position of the powering source must be ~20'' north of FIR4. For the IRc2/I molecular outflow the morphology of the moderate velocity (<60kms^-1) gas shows a weak bipolarity around IRc2/I. The gas at the most extreme velocities does not show any bipolarity around IRc2/I, if any, it is found ~30'' north from these sources. The blue and redshifted gas at moderate velocities shows similar spatial distribution with a systematic trend for the size of the high-velocity gas to decrease as the terminal radial velocity increases. The size-velocity relationship is fitted with a simple velocity law which considers a highly collimated jet and entrained material outside the jet moving in the radial direction. We also find that most of the CO outflowing at moderate velocities is located at the head of the jet. Our results and the spatial distribution and kinematics of the shock tracers in this outflow can be explained if the IRc2/I outflow is driven by a precessing jet oriented along the line of sight.