Kinetic temperature of massive star forming molecular clumps measured
  with formaldehyde
  For a general understanding of the physics involved in the star formation
process, measurements of physical parameters such as temperature and density
are indispensable. The chemical and physical properties of dense clumps of
molecular clouds are strongly affected by the kinetic temperature. Therefore,
this parameter is essential for a better understanding of the interstellar
medium. Formaldehyde, a molecule which traces the entire dense molecular gas,
appears to be the most reliable tracer to directly measure the gas kinetic
temperature.We aim to determine the kinetic temperature with spectral lines
from formaldehyde and to compare the results with those obtained from ammonia
lines for a large number of massive clumps.Three 218 GHz transitions
(JKAKC=303-202, 322-221, and 321-220) of para-H2CO were observed with the 15m
James Clerk Maxwell Telescope (JCMT) toward 30 massive clumps of the Galactic
disk at various stages of high-mass star formation. Using the RADEX non-LTE
model, we derive the gas kinetic temperature modeling the measured para-H2CO
322-221/303-202and 321-220/303-202 ratios. The gas kinetic temperatures derived
from the para-H2CO (321-220/303-202) line ratios range from 30 to 61 K with an
average of 46 K. A comparison of kinetic temperature derived from para-H2CO,
NH3, and the dust emission indicates that in many cases para-H2CO traces a
similar kinetic temperature to the NH3 (2,2)/(1,1) transitions and the dust
associated with the HII regions. Distinctly higher temperatures are probed by
para-H2CO in the clumps associated with outflows/shocks. Kinetic temperatures
obtained from para-H2CO trace turbulence to a higher degree than NH3
(2,2)/(1,1) in the massive clumps. The non-thermal velocity dispersions of
para-H2CO lines are positively correlated with the gas kinetic temperature. The
massive clumps are significantly influenced by supersonic non-thermal motions.
