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

• Published in: The Astrophysical journal 2010-06, Vol.716 (1), p.348-369
• Main Authors: Brusa, M, Civano, F, Comastri, A, Miyaji, T, Salvato, M, Zamorani, G, Cappelluti, N, Fiore, F, Hasinger, G, Mainieri, V, Merloni, A, Bongiorno, A, Capak, P, Elvis, M, Gilli, R, Hao, H, Jahnke, K, Koekemoer, A. M, Ilbert, O, Le Floc'h, E, Lusso, E, Mignoli, M, Schinnerer, E, Silverman, J. D, Treister, E, Trump, J. D, Vignali, C, Zamojski, M, Aldcroft, T, Aussel, H, Bardelli, S, Bolzonella, M, Cappi, A, Caputi, K, Contini, T, Finoguenov, A, Fruscione, A, Garilli, B, Impey, C. D, Iovino, A, Iwasawa, K, Kampczyk, P, Kartaltepe, J, Kneib, J. P, Knobel, C, Kovac, K, Lamareille, F, Leborgne, J.-F, Le Brun, V, Le Fevre, O, Lilly, S. J, Maier, C, McCracken, H. J, Pello, R, Peng, Y.-J, Perez-Montero, E, de Ravel, L, Sanders, D, Scodeggio, M, Scoville, N. Z, Tanaka, M, Taniguchi, Y, Tasca, L, de la Torre, S, Tresse, L, Vergani, D, Zucca, E
• Format: Article
• Language: English
• Subjects: Active galactic nuclei; Astronomy; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COSMIC RAY SOURCES; COSMIC X-RAY SOURCES; Cosmos; Demography; Earth, ocean, space; ENERGY SPECTRA; Exact sciences and technology; GALAXIES; GALAXY NUCLEI; LUMINOSITY; OPTICAL PROPERTIES; PHYSICAL PROPERTIES; RED SHIFT; SPECTRA; SPECTROSCOPY; STARS; UNIVERSE; X-RAY GALAXIES; XMM (spacecraft)
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/716/1/348

We report the final optical identifications of the medium-depth ({approx}60 ks), contiguous (2 deg{sup 2}) XMM-Newton survey of the COSMOS field. XMM-Newton has detected {approx}1800 X-ray sources down to limiting fluxes of {approx}5 x 10{sup -16}, {approx}3 x 10{sup -15}, and {approx}7 x 10{sup -15} erg cm{sup -2} s{sup -1} in the 0.5-2 keV, 2-10 keV, and 5-10 keV bands, respectively ({approx}1 x 10{sup -15}, {approx}6 x 10{sup -15}, and {approx}1 x 10{sup -14} erg cm{sup -2} s{sup -1}, in the three bands, respectively, over 50% of the area). The work is complemented by an extensive collection of multiwavelength data from 24 {mu}m to UV, available from the COSMOS survey, for each of the X-ray sources, including spectroscopic redshifts for {approx}>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 ({approx}95%) have IRAC counterparts, and 1394 ({approx}78%) have MIPS 24 {mu}m 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{sub X} > 44.5 active galactic nuclei (AGNs) is at z {approx} 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 {approx}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{sub X} > 10{sup 44} erg s{sup -1}) X-ray luminosity is {approx}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.