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Title: Effects of external radiation fields on line emission—application to star-forming regions

A variety of astronomical environments contain clouds irradiated by a combination of isotropic and beamed radiation fields. For example, molecular clouds may be irradiated by the isotropic cosmic microwave background, as well as by a nearby active galactic nucleus. These radiation fields excite atoms and molecules and produce emission in different ways. We revisit the escape probability theorem and derive a novel expression that accounts for the presence of external radiation fields. We show that when the field is isotropic the escape probability is reduced relative to that in the absence of external radiation. This is in agreement with previous results obtained under ad hoc assumptions or with the two-level system, but can be applied to complex many-level models of atoms or molecules. This treatment is in the development version of the spectral synthesis code CLOUDY. We examine the spectrum of a Spitzer cloud embedded in the local interstellar radiation field and show that about 60% of its emission lines are sensitive to background subtraction. We argue that this geometric approach could provide an additional tool toward understanding the complex radiation fields of starburst galaxies.
Authors:
;  [1] ;  [2] ;  [3] ;  [4]
  1. University of Kentucky, Lexington, KY 40506 (United States)
  2. AWE plc, Aldermaston, Reading RG7 4PR (United Kingdom)
  3. Department of Physics and Astronomy and Center for Simulational Physics, University of Georgia, Athens, GA 30602-2451 (United States)
  4. Royal Observatory of Belgium, Avenue Circulaire 3, B-1180 Uccle (Belgium)
Publication Date:
OSTI Identifier:
22348458
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 779; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ATOMS; BEAMS; EMISSION; GALAXIES; GALAXY NUCLEI; IRRADIATION; MOLECULES; RADIANT HEAT TRANSFER; RELICT RADIATION; SPECTRA; STARS