Volume 441, Number 2, October II 2005
|Page(s)||417 - 434|
|Section||Cosmology (including clusters of galaxies)|
|Published online||19 September 2005|
Luminosity-dependent evolution of soft X-ray selected AGN
New Chandra and XMM-Newton surveys
Max-Planck-Institut für extraterrestrische Physik, Postf. 1312, 85741 Garching, Germany e-mail: firstname.lastname@example.org
2 Department of Physics, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburg, PA 15213, USA e-mail: email@example.com
3 California Institute of Technology, Pasadena, CA 91125, USA e-mail: firstname.lastname@example.org
Accepted: 10 June 2005
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 , similar to that of optically selected QSO, the space density of low-luminosity AGNs peaks at redshifts below . 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 erg s-1 declines significantly towards high redshifts.
Key words: galaxies: active / X-rays: general
© ESO, 2005
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