A SPECTROSCOPIC STUDY OF THE DR-21 OUTFLOW SOURCE .2. THE VIBRATIONAL H-2 LINE EMISSION

Large-scale mapping and high-spectral resolution profile measurements of the vibrational H-2 v = 1-0 S(1) line are used to investigate the morphology and kinematic structure of the hot, shocked gas associated with the ultraluminous DR 21 young-stellar outflow. It is found that the H-2 line profiles at certain locations within the outflow posses high-velocity wings which extend to beyond 100 km s-1 from the DR 21 rest velocity. We argue that the jets, which shock the surrounding molecular cloud medium and produce the bright H-2 line emission are composed primarily of hot atomic gas which is confined by the thermal pressure of the ambient cloud medium. If this is indeed the case, it is then possible that the periodic clumping of the H-2 jets arise from the interaction of oblique shocks that are formed inside the jets as a result of sudden changes in the external pressure. Alternatively, if the magnetic field strength within the DR 21 cloud core is significantly greater than 30-mu-G, it is more likely that the jets are collimated by the magnetic pressure of the ambient cloud medium.