Entrainment mechanisms for outflows in the L1551 star-forming region

We present high sensitivity (CO)-C-12 and (CO)-C-13 J = 1 -> 0 maps covering the full extent of the parsec-scale L1551 molecular outflow, including the redshifted east-west (EW) flow. We also present (CO)-C-12 J = 3 -> 2 data obtained over a good fraction of the L1551 outflow. We compare the molecular data to wide-field, narrowband optical emission in H alpha. While there are multiple outflows in the L1551 cloud, the main outflow is oriented at 50 degrees position angle and appears to be driven by an embedded source(s) in the central IRS 5 region. The J = 3 -> 2 data indicate that there may be molecular emission associated with the L1551 NE jet, within the redshifted lobe of the main outflow. We have also better defined the EW flow and believe we have identified its blueshifted counterpart. We speculate that the origin of the EW outflow lies near HH 102. Velocity-dependent opacity correction is used to estimate the mass and energy of the outflow. The resulting mass spectral indices from our analysis are systematically lower (less steep) than the power-law indices obtained toward other outflows in several recent studies that use a similar opacity correction method. We show that systematic errors and biases in the mass analysis procedures could result in errors in the determination of the power-law indices. The mass spectral indices, the morphological appearance of the position-velocity plots, and integrated intensity maps of molecular data, compared with the optical, suggest that jet-driven bow shock entrainment is the best explanation for the driving mechanism of outflows in L1551. The kinetic energy of the outflows is found to be comparable to the binding energy of the cloud and sufficient to maintain the turbulence in the L1551 cloud.