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arXiv · 1108.1971

On the missing 2175 Angstroem-bump in the Calzetti extinction curve

Joerg Fischera·Michael Dopita
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Abstract

The aim of the paper is to give a physical explanation of the absence of the feature in the Calzetti extinction curve. We analyze the dust attenuation of a homogeneous source seen through a distant inhomogeneous distant screen. The inhomogeneities are described through an idealized isothermal turbulent medium where the probability distribution function (PDF) of the column density is log-normal. In addition it is assumed that below a certain critical column density the carriers of the extinction bump at 2175 Angstroem are being destroyed by the ambient UV radiation field. Turbulence is found to be a natural explanation not only of the flatter curvature of the Calzetti extinction curve but also of the missing bump provided the critical column density is N_H >= 10^21 cm^-2. The density contrast needed to explain both characteristics is well consistent with the Mach number of the cold neutral medium of our own Galaxy which suggests a density contrast sigma_(rho/ ) 6.

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Joerg Fischera, Michael Dopita. 2011-08-09. On the missing 2175 Angstroem-bump in the Calzetti extinction curve. https://doi.org/10.1051/0004-6361/201116644

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