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Published June 10, 2010 | Published
Journal Article Open

The XMM-Newton Wide-field Survey in the Cosmos Field (XMM-COSMOS): Demography and Multiwavelength Properties of Obscured and Unobscured Luminous Active Galactic Nuclei


We report the final optical identifications of the medium-depth (~60 ks), contiguous (2 deg^2) XMM-Newton survey of the COSMOS field. XMM-Newton has detected ~1800 X-ray sources down to limiting fluxes of ~5 × 10^(–16), ~3 × 10^(–15), and ~7 × 10^(–15) erg cm^(–2) s^(–1) in the 0.5-2 keV, 2-10 keV, and 5-10 keV bands, respectively (~1 × 10^(–15), ~6 × 10^(–15), and ~1 × 10^(–14) erg cm^(–2) s^(–1), in the three bands, respectively, over 50% of the area). The work is complemented by an extensive collection of multiwavelength data from 24 μm to UV, available from the COSMOS survey, for each of the X-ray sources, including spectroscopic redshifts for ≳50% of the sample, and high-quality photometric redshifts for the rest. The XMM and multiwavelength flux limits are well matched: 1760 (98%) of the X-ray sources have optical counterparts, 1711 (~95%) have IRAC counterparts, and 1394 (~78%) have MIPS 24 μm detections. Thanks to the redshift completeness (almost 100%) we were able to constrain the high-luminosity tail of the X-ray luminosity function confirming that the peak of the number density of log L_X > 44.5 active galactic nuclei (AGNs) is at z ~ 2. Spectroscopically identified obscured and unobscured AGNs, as well as normal and star-forming galaxies, present well-defined optical and infrared properties. We devised a robust method to identify a sample of ~150 high-redshift (z > 1), obscured AGN candidates for which optical spectroscopy is not available. We were able to determine that the fraction of the obscured AGN population at the highest (L_X > 10^(44) erg s^(–1)) X-ray luminosity is ~15%-30% when selection effects are taken into account, providing an important observational constraint for X-ray background synthesis. We studied in detail the optical spectrum and the overall spectral energy distribution of a prototypical Type 2 QSO, caught in a stage transitioning from being starburst dominated to AGN dominated, which was possible to isolate only thanks to the combination of X-ray and infrared observations.

Additional Information

© 2010 The American Astronomical Society. Received 2009 December 23; accepted 2010 April 15; published 2010 May 18. Based on data collected at: the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA Inc, under NASA contract NAS 5-26555; the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan; the European Southern Observatory, Chile, under Large Program 175.A-0839; Kitt Peak National Observatory, Cerro Tololo Inter-American Observatory, and the National Optical Astronomy Observatory, which are operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation; and the Canada–France–Hawaii Telescope operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique de France and the University of Hawaii. 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 the USA (NASA). In Germany, the XMM-Newton project is supported by the Bundesministerium f¨ur Wirtschaft und Technologie/Deutsches Zentrum f¨ur Luft- und Raumfahrt (BMWI/DLR, FKZ 50 OX 0001), the Max-Planck Society, and the Heidenhain-Stiftung. Part of this work was supported by the Deutsches Zentrum f¨ur Luft–und Raumfahrt, DLR project numbers 50 OR 0207 and 50 OR 0405. In Italy, the XMM-COSMOS project is supported by PRIN/MIUR under grant 2006-02-5203, ASI-INAF grants I/023/05/00, I/088/06 and ASI/COFIS/WP3110,I/026/07/0. This work was supported in part by NASA Chandra grant number GO7- 8136A (F.C., M.E., A.F., H.H.). T.M. acknowledges support from CONACyT 83564 DGAPA/PAPIIT IN10209 to IAUNAM as well as the NASA ADP (NNX07AT02G) grant to UCSD. G.H. and M.S. acknowledge a contribution from the Leibniz Prize of the Deutsche Forschungsgemeinschaft under the grant HA 1850/28-1. N.C. and A.F. were partially supported from a NASA grant NNX07AV03G to UMBC. K.J. is supported by the Emmy Noether-Programme of the German Science Foundation DFG. E.T. is supported by the National Aeronautics and Space Administration through Chandra Postdoctoral Fellowship Award Number PF8-90055. We thank James Aird and Jacobo Ebrero for sending us machine-readable tables of their X-ray luminosity functions, Desika Narayanan for help with his model SEDs, and Ryan Hickox for providing unpublished information about the X-Bootes survey. We gratefully thank Nick Wright for a carefully reading of the manuscript. This work is based in part on observations obtained with MegaPrime/ MegaCam, a joint project of Canada–France–Hawaii Telescope (CFHT) and CEA/DAPNIA, at the CFHT, and on data products produced at TERAPIX data center located at the Institut d'Astophysique de Paris. This research has made use of the Keck Observatory Archive (KOA), which is operated by the W. M. Keck Observatory and the NASA Exoplanet Science Institute (NExScI), under contract with the National Aeronautics and Space Administration. We gratefully acknowledge the contribution of the entire COSMOS collaboration; more information on the COSMOS survey is available at http://www.astro.caltech.edu/cosmos. This research has made use of the NASA/IPAC Extragalactic Database (NED) and the SDSS spectral archive. Finally, we thank the anonymous referee for detailed and constructive comments to the first version of this paper.

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