Submillimeter Array Observations of the Molecular Outflow in High-mass
  Star-forming Region G240.31+0.07
  We present Submillimeter Array observations toward the 10^{4.7} Lsun
star-forming region G240.31+0.07, in the J=2-1 transition of 12CO and 13CO and
at 1.3 mm continuum, as well as the 12CO and 13CO observations from the Caltech
Submillimeter Observatory to recover the extended emission filtered out by the
interferometer. Maps of the 12CO and 13CO emission show a bipolar, wide-angle,
quasi-parabolic molecular outflow, roughly coincident with an IR nebula
revealed by the Spitzer 3.6 and 4.5 micron emission. The outflow has ~98 Msun
molecular gas, making it one of the most massive molecular outflows known, and
resulting in a very high mass-loss rate of 4.1 by 10^{-3} Msun yr^{-1} over a
dynamical timescale of 2.4 by 10^4 yr. The 1.3 mm continuum observations with a
4" by 3" beam reveal a flattened dusty envelope of ~150 Msun, which is further
resolved with a 1.2" by 1" beam into three dense cores with a total mass of ~40
Msun. The central mm core, showing evidence of active star formation,
approximately coincides with the geometric center of the bipolar outflow thus
most likely harbors the powering source of the outflow. Overall our
observations provide the best case to date of a well-defined wide-angle
molecular outflow in a >10^4 Lsun star-forming region. The outflow is
morphologically and kinematically similar to low-mass protostellar outflows but
has two to three orders of magnitude greater mass, momentum, and energy, and is
apparently driven by an underlying wide-angle wind, hence further supports that
high-mass stars up to late-O types, even in a crowded clustering environment,
can form as a scaled-up version of low-mass star formation.
