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: http://www.arcetri.astro.it/~sbianchi/clumping.html
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Abstract: We present Monte Carlo radiative transfer simulations
for spiral galaxies modelled as a stellar disk and a two-phase clumpy dust
distribution. We divide the volume occupied by the dust into a three-dimensional
grid and assign each cell a clump or smooth medium status. Cell dimension,
clump dust mass and spatial distribution are derived from the observed
properties of Giant Molecular Clouds and molecular gas in the Galaxy. We
produce models for several values of the optical depth and fraction of
the interstellar medium residing in clumps. As a general result, clumpy
models are less opaque than the corresponding homogeneous models. For the
adopted parameters, the increase in the fraction of energy that escapes
the disk is moderate, resulting in surface brightness profiles that are
less than one magnitude brighter than those of the homogeneous models.
The effects of clumping are larger for edge-on views of the disk. This
is in contrast with previous preliminary results for clumping in the literature.
We show how differences arise from the different parametrisation and clump
distribution adopted. We also consider models in which a fraction of the
stellar radiation is emitted within the clumps. In this case, galaxies
are less transparent than in the case when only dust is clumped. The opacity
can be even higher than in the homogeneous case, depending on the fraction
of embedded stellar emission. We point out the implications of the results
for the determination of the opacity and dust mass of spiral galaxies.
A postscript version of the paper is available.
Attenuation: this
file contains the attenuation (i.e. the ratio between the observed flux
and the intrinsic, unextinguished total one) as a function of optical depth
tauV, inclination i, fraction of gas in clumps f_c and fraction of embedded
emission f_emb. 8 values of i are available (Bianchi, Ferrara & Giovanardi,
1996, ApJ, 465, 127). The file is organised as follows:
f_emb tauV -> 0.00 0.15 0.50 0.1 0.5 1.0 2.0 5.0 10.0 0.25 X . . 20 . . . . . . f_c 0.50 . . . 37 . . . . . . 0.75 . . . i 48 . Attenuation . . . X = 58 . . . . . . | 66 . . . . . . where each X is a subset | 75 . . . values . for fixed f_c and f_emb \/ 82 . . . . . . 90 . . . . . .
The attenuation file for the homogeneous case can
be found here
here. The attenuation values
are compatible with those of a S??_ME04 B/T=0 model in the Atlas
of Monte Carlo Models of Dust Extinction in Galaxies for Cosmological Applications
(Ferrara, Bianchi, Cimatti, Giovanardi 1999), the small differences arising
from the different choice of the inclination bands, much narrower in that
work.
| f_emb | ||||
| 0.00 | 0.15 | 0.50 | ||
| 0.25 | 0.1, 0.5, 1.0, 2.0, 5.0, 10. | 0.1, 0.5, 1.0, 2.0, 5.0, 10. | 0.1, 0.5, 1.0, 2.0, 5.0, 10. | |
| f_c | 0.50 | 0.1, 0.5, 1.0, 2.0, 5.0, 10. | 0.1, 0.5, 1.0, 2.0, 5.0, 10. | 0.1, 0.5, 1.0, 2.0, 5.0, 10. |
| 0.75 | 0.1, 0.5, 1.0, 2.0, 5.0, 10. | 0.1, 0.5, 1.0, 2.0, 5.0, 10. | 0.1, 0.5, 1.0, 2.0, 5.0, 10. |
| tauV | ||||||||
| 0.0 | 0.1 | 0.5 | 1.0 | 2.0 | 5.0 | 10. | ||
| 0.25 | 0.075 | 0.375 | 0.75 | 1.5 | 3.75 | 7.5 | ||
| f_c | 0.50 | 0.05 | 0.25 | 0.5 | 1.0 | 2.5 | 5.0 | |
| 0.75 | 0.025 | 0.125 | 0.25 | 0.5 | 1.25 | 2.5 |
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