THE GIANT MOLECULAR OUTFLOW IN MONR2

We present CO J = 1-0, CS J = 2-1, and CS J= 5-4 observations of the energetic molecular outflow and the dense molecular core associated with the Mon R2 infrared cluster. The CO observations are used to determine the mass, energetics, structure, and morphology of the outflow. The outflow is found to have a high degree of collimation over a large angular extent. It is clearly bipolar, although near its origin red- and blue-shifted gas are spatially mixed. In both angular and physical extent this outflow source is among the largest ever studied. Our observations indicate that it is also extremely massive (script M sign ≈200script M sign⊙) and that a significant portion (≈50%) of the surrounding ambient molecular cloud has been swept up by the outflow during the course of its evolution. The outflow has an unusual, bent morphology and is roughly parallel to the direction of the magnetic field in the cloud. The redshifted gas is spatially more confined in the plane of the sky than the blueshifted gas. This may be the result of the effect of the ambient density structure on the outflow and possibly the geometry of the flow. There is also evidence for shell structure in the blueshifted gas, which is not apparent in the redshifted gas. Examination of the velocity field of the outflow reveals a velocity gradient along the flow axis and an apparent acceleration of outflowing gas away from the origin of the flow. The relatively large mass and average density of the outflow indicate that the outflow is primarily comprised of swept-up ambient material. The dynamical timescale shows the Mon R2 flow to be one of the oldest known outflows. Massive and evolved outflows such as the Mon R2 flow can be difficult to recognize and may have escaped detection in other molecular clouds. Yet, they may be important for the dynamical stability and evolution of GMCs. Our CS observations indicate that the dense core which surrounds the infrared cluster at the origin of the outflow has a flattened structure. A velocity gradient of 1 km s-1 pc-1 is found along the major axis of the core suggesting possible rotation about an axis parallel to both the outflow and the magnetic field direction. We place an upper limit on the dynamical mass of the core of ≈ 1000script M sign⊙. Radiative transfer models suggest a density of about 5 × 105 cm-3 in the central regions of the core. Comparison of the spatial distributions of emission from the 2→1 and 5→4 transitions of CS suggests a steep density gradient in the core. Comparison of the binding energy of the core and outflow energy indicates the outflow may be disrupting the core. Investigation of the velocity gradient in the core indicates that if the large-scale 13CO and CS dynamics are representative of precollapse cloud conditions, the cloud could not have conserved angular momentum down to at least 0.3 pc; in fact, Ω∼r-1. This is somewhat difficult to understand in the context of super-critical collapse, and indicates that some cloud braking is occurring on this scale. The overall velocity field in the core suggests significant interaction between the outflow and ambient core.