HCN hyperfine ratio analysis of massive molecular clumps
  We report a new analysis protocol for HCN hyperfine data, based on the
PYSPECKIT package, and results of using this new protocol to analyse a sample
area of seven massive molecular clumps from the Census of High- and Medium-mass
Protostars (CHaMP) survey, in order to derive maps of column density for this
species. There is a strong correlation between the HCN integrated intensity,
IHCN, and previously reported IHCO+ in the clumps, but IN2H+ is not well
correlated with either of these other two "dense gas tracers". The four fitted
parameters from PYSPECKIT in this region fall in the range of VLSR = 8-10 km/s,
{\sigma} V = 1.2-2.2 km/s, Tex = 4-15 K, and {\tau} = 0.2-2.5. These parameters
allow us to derive a column density map of these clouds, without limiting
assumptions about the excitation or opacity. A more traditional (linear) method
of converting IHCN to total mass column gives much lower clump masses than our
results based on the hyperfine analysis. This is primarily due to areas in the
sample region of low I, low Tex, and high {\tau} . We conclude that there may
be more dense gas in these massive clumps not engaged in massive star formation
than previously recognized. If this result holds for other clouds in the CHaMP
sample, it would have dramatic consequences for the calibration of the
Kennicutt-Schmidt star formation laws, including a large increase in the gas
depletion time-scale in such regions.
