Molecular jets in the DR21/W75N high-mass star-forming region
  Molecular jets have been discovered in large numbers, spread throughout star
formation regions. They can usually be traced back to embedded driving
protostars. We here investigate a squadron of such molecular hydrogen jets in
the DR21/W75N region through echelle spectroscopy of the near infrared v=1-0
S(1) emission line centred at 2.122 microns. We detect 79 components, a number
of which possess radial velocities in excess of 80 km/s. The majority of the
components exhibit blue shifts.The regions closer to DR21 exhibit more
blueshifted components suggesting that extinction is important across
individual flows and is higher near DR21. We provide a classification scheme
for the resulting collection of position-velocity diagrams, including other
published data. One prominent class is associated with pairs of shocks well
separated in radial velocity.
  We use hydrodynamic simulations with molecular cooling and chemistry to show
that these are associated with Mach discs and bow shocks. We also employ a
steady-state bow shock model to interpret other revealing position-velocity
diagrams. We consider mechanisms which can generate vibrationally-excited
hydrogen molecules moving at speeds well beyond the breakdown speed permitted
for shock excitation. We conclude that the molecules have formed within the
jets well before being excited by internal shocks triggered by impacts with the
ambient clouds. We also note the relatively high number of high blueshifted
radial velocity components and argue that these must be associated with
high-density molecular jets from Class 0 protostars which are obscured unless
we are selectively viewing within a conical cavity containing the jet.
