THE STRUCTURE AND ENERGETICS OF A HIGHLY COLLIMATED BIPOLAR OUTFLOW -NGC 2264G

We present a detailed observational study of (CO)-C-12 (J = 2-->1) emi ssion from the spectacular bipolar molecular outflow NGC 2264G. These observations enable us to make significantly improved determinations o f the basic physical parameters of the outflow and reveal rich structu ral detail in both its spatial morphology and velocity field. We ident ify a number of robust physical characteristics of the outflow that pr ovide critical challenges for the development of a theoretical underst anding of the dynamical nature of this and other bipolar molecular out flows. In particular, we find that (1) the velocity field of the outfl ow is described by a single ''Hubble'' law to a remarkable degree of p recision over its entire extent, (2) the flow exhibits a high degree o f bipolarity with an intensity contrast between red and blue emission in each lobe of at least a factor of 20, which indicates that the moti on of gas in the outflow is strongly (forwardly) directed along the fl ow major axis, (3) the flow exhibits a well-behaved power-law variatio n of mass with velocity, and (4) the collimation of the flow increases systematically with flow velocity and distance from the driving sourc e, with the highest velocity gas very jetlike in appearance. Moreover, at the highest flow velocities the two oppositely directed lobes disp lay a high degree of similarity in their basic physical properties sug gesting that the underlying wind driving the outflow is characterized by an intrinsic bipolar symmetry which originates with the driving eng ine at the origin of the outflow. Existing outflow theory cannot yet a ccount for the constraints imposed by these observations. In particula r, we find the general result that bow shock models cannot produce the degree of bipolarity required to match the observations of this and o ther outflows. Improved estimates of the outflow's mass, size, and ene rgetics provide strong constraints on the energetics of the driving en gine.