Luminosity-dependent evolution of soft X-ray selected AGN. New Chandra and XMM-Newton surveys
Abstract
We present new results on the cosmological evolution of unabsorbed (type-1) active galactic nuclei (AGN) selected in the soft (0.5-2 keV) X-ray band. From a variety of ROSAT, XMM-Newton and Chandra surveys we selected a total of ~1000 AGN with an unprecedented spectroscopic and photometric optical/NIR identification completeness. For the first time we are able to derive reliable space densities for low-luminosity (Seyfert-type) X-ray sources at cosmological redshifts. The evolutionary behaviour of AGN shows a strong dependence on X-ray luminosity: while the space density of high-luminosity AGN reaches a peak around z∼ 2, similar to that of optically selected QSO, the space density of low-luminosity AGNs peaks at redshifts below z=1. This confirms previous ROSAT findings of a luminosity-dependent density evolution. Using a rigorous treatment of the optical identification completeness we are able to show that the space density of AGN with X-ray luminosities Lx < 1045 erg s-1 declines significantly towards high redshifts.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- October 2005
- DOI:
- 10.1051/0004-6361:20042134
- arXiv:
- arXiv:astro-ph/0506118
- Bibcode:
- 2005A&A...441..417H
- Keywords:
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- galaxies: active;
- X-rays: general;
- Astrophysics
- E-Print:
- 21 pages, 13 figures, A&