A large-scale CO survey of the Rosette Molecular Cloud: assessing the
  effects of O stars on surrounding molecular gas
  We present a new large-scale survey of J=3-2 12CO emission covering 4.8
square degrees around the Rosette Nebula. Approximately 2000 compact clumps are
identified, with a spatially-invariant power law mass distribution index of
-1.8. Most of the inner clumps show velocity gradients of 1-3 km/s/pc, directed
away from the exciting nebula. The gradients decrease with distance from the
central O stars, and are consistent with a photoionised gas acceleration model,
assuming clump lifetimes of a few 10^5 yrs. However, in one clear case, the
observed near-constant velocity gradient is difficult to explain with simple
models. Most blue-shifted but very few of the red-shifted clumps are associated
with dark absorbing optical globules, confirming that the dominant molecular
gas motion is expansion away from the central nebula and O stars. Many clumps
also lie in a molecular ring, having an expansion velocity of 30 km/s, radius
11pc, and dynamical lifetime of ~1Myr. The J=3-2/1-0 12CO line ratios of the
clumps decrease with distance from the O stars, implying a gradient in their
surface temperatures; the results are consistent with a simple model of clump
surface heating due to the central stars.
  Seven high-velocity molecular flows are found in the region, with a close
correspondence between these flows and embedded young clusters. These outflows
are sufficiently energetic to drive local gas turbulence within each cluster.
  We find 14 clear examples of association between embedded young stars seen at
24um and CO clumps; these are thought to be photoevaporating molecular
envelopes. The CO clumps without evidence of embedded stars tend to have lower
velocity gradients, and it is suggested that the presence of the young star may
extend the lifespan of the photoevaporating envelope.
