The distribution of absorbing column densities among Seyfert 2 galaxies

  • Risaliti G
  • Maiolino R
  • Salvati M
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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 (N_H > 10^23 cm^-2) and about half are Compton thick (N_H > 10^24 cm^-2). Intermediate type 1.8-1.9 Seyferts are characterized by an average N_H much lower than "strict" Seyfert 2s. No correlation is found between N_H and the intrinsic luminosity of the nuclear source. This N_H distribution has important consequences for the synthesis of the cosmic X-ray background. Also, 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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Authors

  • G Risaliti

  • R Maiolino

  • M Salvati

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