Infrared Emission from H II Regions

Abstract

view Abstract Citations (77) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Infrared Emission from H II Regions Panagia, Nino Abstract Models of dusty H ii regions have been constructed to study how the power absorbed by dust and reemitted in the infrared depends on the amount, distribution, and properties of dust grains and the spectral type of the exciting star. A large variety of possible situations have been examined. La radiation has been found not to be the dominant source of dust heating unless the optical depth of dust in the ultraviolet is small (and the absorbed power also is small). Nonionizing stellar radiation turned out to be at least as important as the Lyman continuum radiation for the heating of dust. The ratio of the expected infrared luminosity to the La luminosity has been shown to be a sensitive function of both the dust optical depth and the spectral type of the exciting star. A quantity has been defined which is strongly dependent only on the optical depth of the dust present inside an H ii region and which can easily be derived from available radio and infrared data. Very recent and extensive infrared data (Emerson, Jennings, and Moorwood) have been analyzed with the following results: (1) Dust is mixed with gas in compact H ii regions; it absorbs on the average two-thirds of the Lyman continuum radiation; (2) The grains have high infrared absorption efficiency (Q 10-2 at A 50 i ); (3) The average size of grains is larger than 0.05 and smaller than 0.15 (4) The average dust-to-gas mass ratio is 10-2; (5) It is possible that dust in H ii regions is overabundant relative to the interstellar medium. Subject headings: infrared - nebulae Publication: The Astrophysical Journal Pub Date: August 1974 DOI: 10.1086/153054 Bibcode: 1974ApJ...192..221P full text sources ADS | data products SIMBAD (10)