High-Resolution Imaging of Molecular Outflows in Massive Young Stars

We present high angular resolution observations toward two massive star-forming regions, IRAS 18264-1152 and IRAS 23151+5912, with the Plateau de Bure Interferometer (PdBI) in the SiO(J = 2-1) and H¹³CO⁺(J = 1-0) lines and at 1.3 and 3.4 mm continuum, and with the Very Large Array (VLA) in the NH₃(J,K) = (1,1), (2, 2) lines. The NH₃(1, 1) and (2, 2) emission is detected toward IRAS 18264-1152 only. For IRAS 18264-1152, the SiO observations reveal at least two quasi-perpendicular outflows with high collimation factors, and the most dominant feature is a redshifted jetlike outflow with very high velocities up to about Δv = 60 km s^-1 with respect to the systemic velocity. The very high velocity component (Δv = 22-60 km s^-1) of this outflow is spatially offset from its high-velocity (Δv = 3-21 km s^-1) component. The SiO line profiles and position-velocity characteristics of these two components suggest that this outflow could be driven by an underlying precessing jet. For IRAS 23151+5912, the bipolar but mainly blueshifted SiO outflow coincides with the inner parts of the single-dish CO outflow. In particular, the quasi-parabolic shape of the blueshifted outflow coincides with the near-infrared nebulosity and is consistent with entrainment of the gas by an underlying wide-angle wind. The analysis of the molecular outflow data of the two luminous sources further supports high-mass stars forming via a disk-mediated accretion process similar to that in low-mass stars.