Radiation transport in dense interstellar dust clouds. II. Infrared emission from molecular clouds associated with H II regions

Journal Article · Fri Oct 01 00:00:00 EDT 1976 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/154694· OSTI ID:7332105

Leung, C M

Theoretical models are constructed to study the distribution of grain temperature (T/sub d/) and infrared emission from molecular clouds associated with H II regions (with embedded O: B stars). The effects of the following parameters on the temperature structure and the emergent spectrum are studied: grain type (graphite, silicate, and core-mantle grains), optical depth, density inhomogeneity, cloud size, anisotropic scattering, radiation field anisotropy, and characteristics of central heat source. T/sub d/ varies from approximately-greater-than100 K to approximately-less-than20 K throughout the major portion of a cloud, and dielectric grains attain lower temperatures. Due to an inward increase in T/sub d/, the radiation field is strongly forward-peaking, thereby producing a pronounced limb-darkening in the surface brightness. Important features of the computed emission spectra from typical models are compared with available observations, and the importance of beam dilution is emphasized. Theoretical surface brightnesses at selected infrared wavelengths are also presented. The outward radiation pressure on the dust grains is found to exceed the self-gravitational force of the gas over a large portion of a cloud, thus possibly causing the gas in the inner region to expand. Assumptions commonly used in the analysis of infrared observations are examined. Finally, observational methods of deriving the temperature structure (from color and brightness temperatures in the far-infrared), density distribution (from surface brightness at lambdaapproximately-greater-than1 mm), and optical depth (from multiaperture photometry) for the dust component in simple sources are discussed. (AIP)

• Research Organization: National Radio Astronomy Observatory, Green Bank, West Virginia
• OSTI ID: 7332105
• Journal Information: Astrophys. J.; (United States), Vol. 209:1
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
H2 REGIONS
FAR INFRARED RADIATION
INTERSTELLAR GRAINS
RADIATION TRANSPORT
BRIGHTNESS
COSMIC DUST
COSMIC GASES
NEBULAE
OPACITY
SILICATES
COSMIC RADIO SOURCES
DUSTS
ELECTROMAGNETIC RADIATION
FLUIDS
GASES
INFRARED RADIATION
OPTICAL PROPERTIES
OXYGEN COMPOUNDS
PARTICLES
PHYSICAL PROPERTIES
RADIATIONS
SILICON COMPOUNDS
640105* - Astrophysics & Cosmology- Galaxies