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Infrared Dark Clouds are generally assumed to be a promising hunting ground
to trace very early stages of massive star formation. Although IRDCs may
comprise a quite heterogeneous class of objects, high extinction even at
wavelengths as long as 8 micron is a common feature. Hence, Spitzer
observations are a viable tool probe the interior of these objects.
Within our Spitzer/MIPS programme, we have observed several IRDCs at 24 and
70 micron. We indeed find embedded compact objects in these clouds, at least
at 24 micron. By means of first radiative transfer considerations and by
comparing the Spitzer data with our 1.2-mm single dish data for these IRDCs,
we try to estimate the energetics of these constituents. Are these really the
seeds for massive (proto-)clusters? Together with the extinction information
one can derive from the Spitzer absorption data at shorter wavelengths
(GLIMPSE, 3 - 9 micron), we will attempt to give first ideas of the structure
of the IRDCs under study.
We mention that on the basis of these continuum data alone, it is not possible
to assert dynamical parameters of the gas within our IRDCs. However, if the
approved ATCA 3-mm observations for our IRDCs in the beginning of August 2006
are successful, we should be able to compare the Spitzer maps with N2H+(1-0)
maps at comparable spatial resolution. The dynamical state of the dense gas
can be assessed and the question can be addressed whether the gas is quiescent
overall or more disturbed in the vicinity of Spitzer point sources.
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