The Anatomy of Dense Molecular Clouds
At mm/submm wavelengths, where the Rayleigh-Jeans approximation applies and dust optical depths are small, the observed surface brightness of dust emission is S v /ΩA∝NHσ v H Td. Here NH is the hydrogen column density, σ v H is the dust absorption cross section per H-atom at the frequency v and Td is the dust temperature. For volume densities nH ⩽1E5–1E6cm-3 molecular spectroscopy and dust continuum observations in general yield comparable results. But at higher volume densities and low gas temperatures it is found that molecular spectroscopy becomes an unreliable tracer of hydrogen column densities. Continuum observations of dust emission, on the other hand, provide the most reliable method of investigating especially very compact cores of molecular clouds, since σ v H and Td are usually known within factors of 2 or better. As examples recent observations of star forming cloud cores in the Orion A and B clouds and of two giant molecular clouds in the galactic center region will be summarizeded in this review.
KeywordsMolecular Cloud Dust Emission Galactic Center Cloud Core Dust Temperature
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