Analytical approximations for calculating the escape and absorption of radiation in clumpy dusty environments

Authors
Citation
F. Varosi et E. Dwek, Analytical approximations for calculating the escape and absorption of radiation in clumpy dusty environments, ASTROPHYS J, 523(1), 1999, pp. 265-305
Citations number
42
Categorie Soggetti
Space Sciences
Journal title
ASTROPHYSICAL JOURNAL
ISSN journal
0004637X → ACNP
Volume
523
Issue
1
Year of publication
1999
Part
1
Pages
265 - 305
Database
ISI
SICI code
0004-637X(19990920)523:1<265:AAFCTE>2.0.ZU;2-A
Abstract
We present analytical approximations for calculating the scattering, absorp tion, and escape of non-ionizing photons from a spherically symmetric two-p hase clumpy medium, with either a central point source of isotropic radiati on, a uniform distribution of isotropic emitters, or uniformly illuminated by external sources. The analytical approximations are based on the mega-gr ains model of two-phase clumpy media, as proposed by Hobson & Padman, combi ned with escape and absorption probability formulae for homogeneous media. The accuracy of the approximations is examined by comparison with three-dim ensional Monte Carlo simulations of radiative transfer, including multiple scattering. Our studies show that the combined mega-grains and escape/absor ption probability formulae provide a good approximation of the escaping and absorbed radiation fractions for a wide range of parameters characterizing the clumpiness and optical properties of the medium. A realistic test of t he analytic approximations is performed by modeling the absorption of a sta rlike source of radiation by interstellar dust in a clumpy medium and by ca lculating the resulting equilibrium dust temperatures and infrared emission spectrum of both the clumps and the interclump medium. In particular, we f ind that the temperature of dust in clumps is lower than in the interclump medium if the clumps are optically thick at wavelengths at which most of th e absorption occurs. Comparison with Monte Carlo simulations of radiative t ransfer in the same environment shows that the analytic model yields a good approximation of dust temperatures and the emerging UV-FIR spectrum of rad iation for all three types of source distributions mentioned above. Our ana lytical model provides a numerically expedient way to estimate radiative tr ansfer in a variety of interstellar conditions and can be applied to a wide range of astrophysical environments, from clumpy star-forming regions to s tal;burst galaxies.