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Our knowledge about the first stages of massive star and cluster formation
is still limited. Several studies are underway to trace related objects by
means of (sub-)mm continuum surveys in the vicinity of more evolved
objects. On the other hand, recent mid-infrared satellite surveys of the
Galactic plane have revealed a plethora of infrared-dark clouds (IRDCs),
suggested by initial studies to be a good hunting ground for very early
stages of (high-mass) star formation.
We present the first results of our program to study the properties of a
new sample of IRDCs in the southern hemisphere where ALMA will play a
major role in the intermediate future.
To investigate the dust content in the IRDCs we cross-correlated 1.2 mm
continuum data from SIMBA@SEST with mid- infrared Spitzer/GLIMPSE images.
Thus, we were able to establish the connection between emission sources at
millimeter wavelengths and the dark clouds we see at 8 micron. We
extracted masses and column densities, which are important quantities in
the characterization of the initial conditions of massive star formation.
The total masses of the IRDCs were found to range from 200 to 3200 solar
masses, hence qualifying the regions to be well capable of forming massive
stars.
The results for the column densities will be discussed with regard to
recent predictions from theoretical high-mass star formation models. In
particular, we employ the extinction map technique to derive masses and
column densities from the mid-infrared data that provide a much better
spatial resolution (2”-3”) compared to (sub-)mm single-dish
data (15”-24”) and allow such parameter estimations in a
temperature-independent fashion. We demonstrate that these advantages turn
the extinction map approach into a promising technique to efficiently
analyse the huge number of catalogued IRDCs.
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