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|Title:||Compton thick AGN in the XMM-COSMOS survey||Authors:||LANZUISI, Giorgio
Rosario, D. J.
|Issue Date:||2015||Journal:||ASTRONOMY & ASTROPHYSICS||Number:||573||First Page:||A137||Abstract:||Heavily obscured, Compton thick (CT, N<SUB>H</SUB>> 10<SUP>24</SUP> cm<SUP>-2</SUP>) active galactic nuclei (AGN) may represent an important phase in AGN/galaxy co-evolution and are expected to provide a significant contribution to the cosmic X-ray background at its peak. However, unambiguously identifying CT AGN beyond the local Universe is a challenging task even in the deepest X-ray surveys, and given the expected low spatial density of these sources in the 2-10 keV band, large area surveys are needed to collect sizable samples. Through direct X-ray spectra analysis, we selected 39 heavily obscured AGN (N<SUB>H</SUB>>3 × 10<SUP>23</SUP> cm<SUP>-2</SUP>) at bright X-ray fluxes (F<SUB>2-10</SUB> ≳ 10<SUP>-14</SUP> erg s<SUP>-1</SUP> cm<SUP>-2</SUP>) in the 2 deg<SUP>2</SUP> XMM-COSMOS survey. After selecting CT AGN based on the fit of a simple absorbed two power law model to the shallow XMM-Newton data, the presence of bona fide CT AGN was confirmed in 80% of the sources using deeper Chandra data and more complex models. The final sample comprises ten CT AGN (six of them also have a detected Fe Kα line with EW ~ 1 keV), spanning a wide range of redshifts (z ~ 0.1-2.5) and luminosity (L<SUB>2-10</SUB> ~ 10<SUP>43.5</SUP>-10<SUP>45</SUP> erg s<SUP>-1</SUP>) and is complemented by 29 heavily obscured AGN spanning the same redshift and luminosity range. We collected the rich multi-wavelength information available for all these sources, in order to study the distribution of super massive black hole and host properties, such as black hole mass (M<SUB>BH</SUB>), Eddington ratio (λ<SUB>Edd</SUB>), stellar mass (M<SUB>∗</SUB>), specific star formation rate (sSFR) in comparison with a sample of unobscured AGN. We find that highly obscured sources tend to have significantly smaller M<SUB>BH</SUB> and higher λ<SUB>Edd</SUB> with respect to unobscured sources, while a weaker evolution in M<SUB>∗</SUB> is observed. The sSFR of highly obscured sources is consistent with the one observed in the main sequence of star forming galaxies, at all redshifts. We also present and briefly discuss optical spectra, broadband spectral energy distribution (SED) and morphology for the sample of ten CT AGN. Both the optical spectra and SED agree with the classification as highly obscured sources: all the available optical spectra are dominated by the stellar component of the host galaxy, and to reproduce the broadband SED, a highly obscured torus component is needed for all the CT sources.Exploiting the high resolution Hubble-ACS images available, we are able to show that these highly obscured sources have a significantly larger merger fraction with respect to other X-ray selected samples of AGN. Finally we discuss the implications of our findings in the context of AGN/galaxy co-evolutionary models, and compare our results with the predictions of X-ray background synthesis models. Appendices are available in electronic form at <http://www.aanda.org/10.1051/0004-6361/201424924/olm||Acknowledgments:||We thank the anonymous referee for constructive comments that have helped us to improve the quality of this paper. The authors thank M. Brightman for useful discussions on the X-ray selection of CT AGN. G.L. and M.B. acknowledge support from the FP7 Career Integration Grant eEASy (CIG 321913). G.L. acknowledges support from the PRIN 2011/2012. K.I. acknowledges support by DGI of the Spanish Ministerio de Economía y Competitividad (MINECO) under grant AYA2013-47447-C3-2-P. This work benefited from the thales project 383549 that is jointly funded by the European Union and the Greek Government in the framework of the programme “Education and lifelong learning”. This work is based on observations obtained with XMM-Newton , an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. Also based on observations made with Chandra X-ray satellite, founded by NASA. This research has made use of data and/or software provided by the High Energy Astrophysics Science Archive Research Center (HEASARC), which is a service of the Astrophysics Science Division at NASA/GSFC and the High Energy Astrophysics Division of the Smithsonian Astrophysical Observatory.||URI:||http://hdl.handle.net/20.500.12386/23689||URL:||https://www.aanda.org/articles/aa/abs/2015/01/aa24924-14/aa24924-14.html||ISSN:||0004-6361||DOI:||10.1051/0004-6361/201424924||Bibcode ADS:||2015A&A...573A.137L||Fulltext:||open|
|Appears in Collections:||1.01 Articoli in rivista|
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