EDP Sciences
Free Access
Volume 507, Number 2, November IV 2009
Page(s) 747 - 756
Section Extragalactic astronomy
DOI https://doi.org/10.1051/0004-6361/200912395
Published online 08 September 2009
A&A 507, 747-756 (2009)
DOI: 10.1051/0004-6361/200912395

The Compton-thick AGN in the Chandra Deep Field North

I. Georgantopoulos1, A. Akylas1, A. Georgakakis1, and M. Rowan-Robinson2

1  Institute of Astronomy & Astrophysics, National Observatory of Athens, Palaia Penteli, 15236 Athens, Greece
    e-mail: ig@astro.noa.gr
2  Astrophysics Group, Blackett Laboratory, Imperial College, Prince Consort Road, SW7 2BZ, UK

Received 27 April 2009 / Accepted 22 August 2009

We present X-ray spectral analysis of the brightest sources ( $f_{2{-}10~{\rm keV}} > 10^{-15}$  $\rm erg\,cm^{-2}\,s^{-1}$) in the Chandra Deep Field North. Our sample consists of 222 sources; for the vast majority (171) either a spectroscopic or a photometric redshift is available. Our goal is to discover the Compton-thick AGN in a direct way i.e. through their X-ray spectra. Compton-thick AGN give away their presence in X-rays either directly through the absorption turnover redshifted in the Chandra passband, or through a flat, reflection-dominated, spectrum. The above selection criteria yield 10 Compton-thick AGN candidates of which the nine are reflection dominated. The IR or sub-mm data where available, corroborate the presence of a heavily obscured nucleus in most cases. All the five candidate Compton-thick sources with available 24 $\mu$m data present very high values of the f24/$f_{\rm R}$ flux ratio suggesting that they are dust obscured galaxies. The low fx/ $f_{\rm IR}$ ratio also suggest the presence of obscured nuclei in many cases. Four of the candidate Compton-thick sources are associated with sub-mm galaxies at high redshifts $z \sim 2$. The number count vs. flux distribution of the candidate Compton-thick AGN as well as their distribution with redshift agree reasonably well with the predictions of the X-ray background synthesis models of Gilli et al.

Key words: X-rays: general -- X-rays: diffuse background -- X-rays: galaxies -- infrared: galaxies

© ESO 2009

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.