The Gas Properties of the W3 GMC: A HARP study
  We present 12CO, 13CO and C18O J=3-2 maps of the W3 GMC made at the James
Clerk Maxwell Telescope. We combine these observations with Five Colleges Radio
Astronomy Observatory CO J=1-0 data to produce the first map of molecular-gas
temperatures across a GMC and the most accurate determination of the mass
distribution in W3 yet obtained. We measure excitation temperatures in the part
of the cloud dominated by triggered star formation (the High Density Layer,
HDL) of 15-30 K, while in the rest of the cloud, which is relatively unaffected
by triggering (Low Density Layer, LDL), the excitation temperature is generally
less than 12 K. We identify a temperature gradient in the HDL which we
associate with an age sequence in the embedded massive star-forming regions. We
measure the mass of the cloud to be 4.4+/-0.4 x 10^5 solar masses, in agreement
with previous estimates. Existing sub-mm continuum data are used to derive the
fraction of gas mass in dense clumps as a function of position in the cloud.
This fraction, which we interpret as a Clump Formation Efficiency (CFE), is
significantly enhanced across the HDL, probably due to the triggering. Finally,
we measure the 3D rms Mach Number as a function of position and find a
correlation between the Mach number and the CFE within the HDL only. This
correlation is interpreted as due to feedback from the newly-formed stars and a
change in its slope between the three main star-forming regions is construed as
another evolutionary effect. We conclude that triggering has affected the
star-formation process in the W3 GMC primarily by creating additional dense
structures that can collapse into stars. Any traces of changes in CFE due to
additional turbulence have since been overruled by the feedback effects of the
star-forming process itself.
