High-latitude molecular clouds and infrared cirrus

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1988

OSTI ID:5469974

de Vries, H W

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
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics & Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
CLOUDS
DUSTS
ELECTROMAGNETIC RADIATION
FAR INFRARED RADIATION
GALAXIES
INFRARED RADIATION
INFRARED SPECTRA
INTERSTELLAR SPACE
MILKY WAY
MOLECULES
RADIATIONS
SPACE
SPECTRA
THERMAL RADIATION