Astronomy and Astrophysics, volume 533A, 117-117 (2011/9-1)
On the missing 2175 Å-bump in the Calzetti extinction curve.
FISCHERA J. and DOPITA M.
Abstract (from CDS):
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 2175Å 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 NHlog≥1021cm–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 σρ/<ρ>≃6.