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We developed a novel method to unbiasedly select massive clouds by
determining mid infrared extinction maps from the GLIMPSE point source catalog.
A first view of the clouds was provided by bolometer imaging with MAMBO at the 30m telescope,
revealing various cloud structures (often filamentary) and allowing mass estimates of ~ 10^4 - 10^5 Msun per cloud.
We find various condensations, clumps of sub parsec sizes, to be present in the clouds,
sometimes several clumps per cloud.
We derived rotational temperatures and kinematic distances from ammonia observations performed with the Effelsberg 100m telescope.
A combination of the data points to a large variety in the
characteristics of the clouds. Firstly,
we have "quiescent" clouds with weak dust emission containing
no clumps, the clouds are cold (12-16 K) and IR dark. The second
"peaked" clouds have one clump per cloud, their temperatures are
higher (till 25 K) and some sources show the higher J,K=(3,3)
transitions of ammonia, but the line widths are still narrow (~ 1-2
km/s). The last category, has multiple clumps per cloud: these clouds have very strong
dust emission, the IR background is not always dark, the line widths
are wider indicating more turbulence in the cloud and the strong
presence ammonia J,K=(3,3) points to internal heating sources, possibly massive protostellar clusters?
These various types of clouds seem to represent a evolutionary
sequence: from the more dark, cold and quiescent clouds to the
brighter, hotter and more active ones. We will present the analyzed
data for 23 so-called high extinction clouds and provide a
possible interpretation in the shape of a evolutionary scheme in the
early phases of massive star formation based on the MAMBO
bolometer and the Effelsberg ammonia data.
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