Astronomy and Astrophysics – Astronomy
Scientific paper
Mar 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008head...10.2615d&link_type=abstract
American Astronomical Society, HEAD meeting #10, #26.15
Astronomy and Astrophysics
Astronomy
Scientific paper
X-ray surveys have revealed a population of objects with fx/fopt > 10, i. e. more than a factor 10 higher than typical X-ray selected AGN. The true nature of these extreme objects, termed EXOs, is still not fully understood. A significant fraction of the EXO population has been found to exhibit very red optical-NIR colours (R-K > 5) and shows signatures of substantial absorption in X-rays. These objects are the best candidates to be the mostly elusive type 2 QSOs, required by synthesis models of the X-ray background.
Here we present the multi-wavelength properties of one of the largest samples of bright EXOs assembled so far (fx > 10^-13 erg/cm^2/s, 0.2-12 keV), drawn from the cross-correlation between 2XMMp and SDSS-DR5 catalogues. Using detailed analysis of the XMM-Newton spectra and X-ray colours, we are able to place limits on the size of the obscured population represented by our sample. UKIRT near-IR data, obtained for 40% of our EXOs, show evidence of substantial reddening for most of them, supporting the classification of type 2 AGN. We also investigate further constraints on the nature of these objects obtained via simple modeling of the AGN population incorporating realistic distribution of the nuclear obscuration and highlight the surprising results on the most extreme object in our sample for which near-IR spectroscopy has been obtained.
We acknowledge the SPARTAN support under the contract MEST-CT-2004-7512.
Del Moro Agnese
Mateos Silvia
Watson Michael G.
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