High-latitude molecular clouds and infrared cirrus
The high-latitude infrared cirrus detected by IRAS is identified with atomic and molecular clouds. These clouds are small (usually less than 1 sq. deg.) and show weak CO emission. On the basis of a distance of 100 pc they are characterized by a mass of a few solar masses and a radius of about 1 pc. Thermal radiation by dust as a results of heating by the diffuse interstellar radiation field is the most-plausible origin of the cirrus emission at far-infrared wavelengths. On the basis of plausible assumptions regarding the uniformity of both the gas-to-dust ratio and the heating and cooling of the dust, the flux density at 100 {mu}m from regions with low visual extinction should be a good tracer of the gas column density. Indeed, the data show an approximately linear proportionality between N(HI), obtained from 21-cm observations, and I{sub 100} (HI), the flux density from dust associated with HI. If the ratio of column density to flux density in high-latitude molecular clouds is equal to the corresponding relation in atomic ones, a value for the ratio of H{sub 2} column density to CO velocity-integrated radiation temperature may be obtained. Although low-mass clouds may be large in number, the fraction of the Galactic molecular mass in the form of these clouds is probably no more than 1%.
- Research Organization:
- Columbia Univ., New York, NY (USA)
- OSTI ID:
- 5469974
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
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