Dust and gas temperatures in dense molecular clouds

Details Dust and gas temperatures in dense molecular clouds Dust and gas temperatures in dense molecular clouds

Jan 1984

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984a%26a...130....5k&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 130, no. 1, Jan. 1984, p. 5-10.

Astronomy and Astrophysics

Astrophysics

44

Cosmic Dust, Gas Temperature, Molecular Clouds, Astronomical Models, Optical Thickness, Particle Size Distribution, Temperature Distribution

Scientific paper

Calculations are performed on the relationship between gas and dust temperatures for the situation where the main heat input to the gas is due to collisions with hot grains. The grains have a wide distribution of sizes and, consequently, a wide distribution of temperatures. It is found that, under many circumstances, the molecular gas is heated by small graphite grains whose temperature can be considerably larger than the silicate grains whose emission dominates the far-infrared spectrum. This can cause the gas temperature to appear larger than the dust temperature. The extreme case is found to be when one tenth of the solar carbon abundance is in the form of 100 A graphite particles and all of solar silicon is present as micron sized olivine grains. Radiative transport calculations of a spherical model cloud heated from the outside show that, in this situation, the gas temperature can be twenty percent larger than the color temperature deduced from the infrared spectrum. Large differences between gas and dust color temperature can also occur when the dust is highly optically thick (100 visual magnitudes) and there are embedded heat sources within the cloud. A brief comparison is made with observational data available for the nearby dust cloud B 35 as well as for the galactic center molecular clouds.

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