The XMM-Newton Wide-field Survey in the Cosmos Field (XMM-COSMOS): Demography and Multiwavelength Properties of Obscured and Unobscured Luminous Active Galactic Nuclei
Finoguenov, A.; Aussel, H.; Le Floc'h, E.; Ilbert, O.; Taniguchi, Y.; Jahnke, K.; Silverman, J. D.; Treister, E.; Salvato, M.; Merloni, A.; Fiore, F.; Bolzonella, M.; Vignali, C.; Gilli, R.; Comastri, A.; Iwasawa, K.; Cappelluti, N.; Brusa, M.; Tanaka, M.; Hasinger, G.; Mainieri, V.; Capak, P.; Koekemoer, A. M.; Schinnerer, E.; Scoville, N. Z.; Caputi, K.; Civano, F.; Elvis, M.; McCracken, H. J.; Sanders, D.; Mignoli, M.; Zamorani, G.; Tasca, L.; Kneib, J. P.; Kartaltepe, J.; Garilli, B.; Bardelli, S.; Zucca, E.; Cappi, A.; Scodeggio, M.; Hao, H.; Bongiorno, A.; Lusso, E.; Impey, C. D.; Lilly, S. J.; Zamojski, M.; Pello, R.; Contini, T.; Tresse, L.; Kampczyk, P.; Fruscione, A.; de la Torre, S.; de Ravel, L.; Iovino, A.; Knobel, C.; Lamareille, F.; Le Brun, V.; Maier, C.; Vergani, D.; Miyaji, T.; Kovac, K.; Perez-Montero, E.; Le Fevre, O.; Aldcroft, T.; Trump, J. D.; Leborgne, J. -F.; Peng, Y. -J.
Germany, United States, Italy, Mexico, France, Japan, United Kingdom, Switzerland
Abstract
We report the final optical identifications of the medium-depth (~60 ks), contiguous (2 deg2) 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 gsim50% 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 LX > 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 (LX > 1044 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.
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.