The Distribution of Absorbing Column Densities among Seyfert 2 Galaxies
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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 1999
- DOI:
- 10.1086/307623
- arXiv:
- arXiv:astro-ph/9902377
- Bibcode:
- 1999ApJ...522..157R
- Keywords:
-
- GALAXIES: ACTIVE;
- GALAXIES: NUCLEI;
- GALAXIES: SEYFERT;
- X-RAYS: GALAXIES;
- Galaxies: Active;
- Galaxies: Nuclei;
- Galaxies: Seyfert;
- X-Rays: Galaxies;
- Astrophysics
- E-Print:
- 16 LaTeX pages+5 postscript figures, accepted by ApJ