EDP Sciences
Free access
Issue
A&A
Volume 441, Number 2, October II 2005
Page(s) 417 - 434
Section Cosmology (including clusters of galaxies)
DOI http://dx.doi.org/10.1051/0004-6361:20042134


A&A 441, 417-434 (2005)
DOI: 10.1051/0004-6361:20042134

Luminosity-dependent evolution of soft X-ray selected AGN

New Chandra and XMM-Newton surveys
G. Hasinger1, T. Miyaji2 and M. Schmidt3

1  Max-Planck-Institut für extraterrestrische Physik, Postf. 1312, 85741 Garching, Germany
    e-mail: ghasinger@mpe.mpg.de
2  Department of Physics, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburg, PA 15213, USA
    e-mail: miyaji@cmu.edu
3  California Institute of Technology, Pasadena, CA 91125, USA
    e-mail: mxs@astro.caltech.edu

(Received 7 October 2004 / Accepted 10 June 2005 )

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 $z\sim 2$, 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 $L_{\rm x} < 10^{45}$ erg s-1 declines significantly towards high redshifts.


Key words: galaxies: active -- X-rays: general

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