Continuum and Spectral Line Radiation from a Random Clumpy Medium
Journal article, 2018

The American Astronomical Society. All rights reserved. We present a formalism for continuum and line emission from random clumpy media together with its application to problems of current interest, including CO spectral lines from ensembles of clouds and radio emission from H ii regions, supernovae, and star-forming regions. For line emission, we find that the effects of clump opacity on observed line ratios can be indistinguishable from variations of intrinsic line strengths, adding to the difficulties in determining abundances from line observations. Our formalism is applicable to arbitrary distributions of cloud properties, provided the cloud volume filling factor is small; numerical simulations show it to hold up to filling factors of ∼10%. We show that irrespective of the complexity of the cloud ensemble, the radiative effect of clumpiness can be parameterized at each frequency by a single multiplicative correction to the overall optical depth; this multiplier is derived from appropriate averaging over individual cloud properties. Our main finding is that cloud shapes have only a negligible effect on radiation propagation in clumpy media; the results of calculations employing point-like clouds are practically indistinguishable from those for finite-sized clouds with arbitrary geometrical shapes.

H II regions

ISM: abundances

radiative transfer

line: formation

supernovae: general

line: profiles


John Conway

Chalmers, Space, Earth and Environment, Onsala Space Observatory

Moshe Elitzur

University of Kentucky

University of California

Rodrigo Parra Barraza

European Southern Observatory Santiago

Astrophysical Journal

0004-637X (ISSN) 1538-4357 (eISSN)

Vol. 865 1 70

Subject Categories

Meteorology and Atmospheric Sciences

Astronomy, Astrophysics and Cosmology

Other Physics Topics



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