EDP Sciences
Free access
Issue A&A
Volume 459, Number 3, December I 2006
Page(s) 693 - 701
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20054632

A&A 459, 693-701 (2006)
DOI: 10.1051/0004-6361:20054632

XMM-Newton and Chandra measurements of the AGN intrinsic absorption: dependence on luminosity and redshift

A. Akylas1, I. Georgantopoulos1, A. Georgakakis2, S. Kitsionas3, and E. Hatziminaoglou4

1  Institute of Astronomy & Astrophysics, National Observatory of Athens, I. Metaxa & B. Pavlou, Penteli, 15236, Athens, Greece
    e-mail: th@astro.noa.gr
2  Physics Department, Imperial College of Science Technology and Medicine, Blackett Laboratory, Prince Consort Rd, 2BZ SW7, London, UK
3  Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482, Potsdam, Germany
4  Institute de Astrofisica de Canarias, C/via Lactea s/n, 38200 La Laguna, Spain

(Received 2 December 2005 / Accepted 8 June 2006 )

We combine bright XMM-Newton data with the Chandra Deep Field South observations to explore the behavior of the intrinsic AGN absorption, as a function of redshift and luminosity. Our sample consists of 359 sources selected in the hard 2-8 keV band, spanning the flux range 6 $\times$ 10-16-3 $\times$ 10-13 $\rm erg~cm^{-2}~s^{-1}$ with a high rate of spectroscopic or photometric redshift completeness (100 and 85 per cent respectively for the Chandra and XMM-Newton data). We derive the column density values using X-ray spectral fits. We find that the fraction of obscured AGN falls with increasing luminosity in agreement with previous findings. The fraction of obscured AGN shows an apparent increase at high redshifts (z>2). Simulations show that this effect can most probably be attributed to the fact that at high redshifts the column densities are overestimated.

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

© ESO 2006

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.
  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.

Editor-in-Chief: T. Forveille
Letters Editor-in-Chief: J. Alves
Managing Editor: C. Bertout

ISSN: 0004-6361 ; e-ISSN: 1432-0746
Frequency: 12 volumes per year
Published by: EDP Sciences

Mirror sites: CDS | EDP Sciences
  RSS feeds
© The European Southern Observatory (ESO)