The Distribution of Absorbing Column Densities among Seyfert 2 Galaxies

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Abstract
We use hard X-ray data for an "optimal" sample of Seyfert 2 galaxies to derive the distribution of the gaseous absorbing column densities among obscured active nuclei in the local universe. Of all Seyfert 2 galaxies in the sample, 75% are heavily obscured (NH > 1023 cm-2), and about half are Compton thick (NH > 1024 cm-2). Intermediate type 1.8-1.9 Seyfert galaxies are characterized by an average NH much lower than "strict" Seyfert 2 galaxies. No correlation is found between NH and the intrinsic luminosity of the nuclear source. This NH distribution has important consequences for the synthesis of the cosmic X-ray background. In addition, the large fraction of Compton-thick objects implies that most of the obscuring gas is located within a radius of a few 10 pc from the nucleus.
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