Astron. Astrophys. 364, 769-779 (2000)

5. Conclusion and outlook

The combined ISOSS 170 µm and IRAS 100 µm data sets are a useful tool to characterize cold dust in galactic molecular clouds and to find cloud cores with very low FIR colour temperatures. The main findings of our investigation in the test region Chamaeleon are as follows:

• The dust colour temperature is K for the intercloud medium and around 14 K inside the ¹³CO clouds.

• The comparison of 170 µm emission with optical extinction has shown a linear correlation up to 7 mag. This qualifies as a good tracer of dust column density.

• We have found (Boulanger et al. (1998)) well correlated with , which finally proves the assumption that combined IRAS 60 µm and 100 µm bands can be used to locate clouds with cold dust.

• We have developed a method for finding very cold cores, and located 9 VCCs. Comparison of our VCCs with earlier near infrared and CO surveys has proven that these objects are indeed highly opaque molecular cloud cores.

• The VCCs have high gas column densities and low CO excitation temperatures, .

• The phisical parameters of the very cold cores agree with the results of radiative transfer calculations for a spherical model cloud heated from outside by one third of the ISRF at the solar neighbourhood.

The sample we will obtain analysing the complete ISOSS database ( 15 % of the sky) is much larger than any of the previous FIR samples. The very cold core search will be extended to the giant molecular cloud complexes in Orion, Taurus, Cepheus, Cygnus and Ophiuchus. Extrapolating the results of our Chamaeleon survey, we expect to detect more than a hundred very cold cloud cores in the Milky Way. A series of follow-up measurements in cm, mm and sub-mm wavelengths has been started in order to derive the physical properties of the gas in the very cold cores.

© European Southern Observatory (ESO) 2000

Online publication: January 29, 2001
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