The Structure and Energetics of a Highly Collimated Bipolar Outflow: NGC 2264G

We present a detailed observational study of 12CO (J = 2 1) emission from the spectacular bipolar molecular outflow NGC 2264G. These observations enable us to make significantly improved determinations of the basic physical parameters of the outflow and reveal rich structural detail in both its spatial morphology and velocity field. We identify a number of robust physical characteristics of the outflow that provide critical challenges for the development of a theoretical understanding of the dynamical nature of this and other bipolar molecular outflows. In particular, we find that (1) the velocity field of the outflow is described by a single "Hubble" law to a remarkable degree of precision over its entire extent, (2) the flow exhibits a high degree of bipolarity with an intensity contrast between red and blue emission in each lobe of at least a factor of 20, which indicates that the motion of gas in the outflow is strongly (forwardly) directed along the flow major axis, (3) the flow exhibits a well-behaved power-law variation of mass with velocity, and (4) the collimation of the flow increases systematically with flow velocity and distance from the driving source, with the highest velocity gas very jetlike in appearance. Moreover, at the highest flow velocities the two oppositely directed lobes display a high degree of similarity in their basic physical properties suggesting that the underlying wind driving the outflow is characterized by an intrinsic bipolar symmetry which originates with the driving engine at the origin of the outflow. Existing outflow theory cannot yet account for the constraints imposed by these observations. In particular, we find the general result that bow shock models cannot produce the degree of bipolarity required to match the observations of this and other outflows. Improved estimates of the outflow's mass, size, and energetics provide strong constraints on the energetics of the driving engine.