CO multi-line observations of HH 80-81: a two-component molecular
  outflow associated with the largest protostellar jet in our Galaxy
  Stretching a length reaching 10 pc projected in the plane of sky, the radio
jet associated with Herbig-Haro objects 80 and 81 (HH 80-81) is known as the
largest and best collimated protostellar jet in our Galaxy. The nature of the
molecular outflow associated with this extraordinary jet remains an unsolved
question which is of great interests to our understanding of the relationship
between jets and outflows in high-mass star formation. Here we present Atacama
Pathfinder EXperiment CO(6-5) and (7-6), James Clerk Maxwell Telescope CO(3-2),
Caltech Submillimeter Observatory CO(2-1), and Submillimeter Array CO and
$^{13}$CO(2-1) mapping observations of the outflow. We report on the detection
of a two-component outflow consisting of a collimated component along the jet
path and a wide-angle component with an opening angle of about $30^{\circ}$.
The gas velocity structure suggests that each of the two components traces part
of a primary wind. From LVG calculations of the CO lines, the outflowing gas
has a temperature around 88 K, indicating that the gas is being heated by
shocks. Based on the CO(6-5) data, the outflow mass is estimated to be a few
$M_{\odot}$, which is dominated by the wide-angle component. A comparison
between the HH 80-81 outflow and other well shaped massive outflows suggests
that the opening angle of massive outflows continues to increase over time.
Therefore, the mass loss process in the formation of early-B stars seems to be
similar to that in low-mass star formation, except that a jet component would
disappear as the central source evolves to an ultracompact HII region.
