Chandra and Spitzer Unveil Heavily Obscured Quasars in the Chandra/SWIRE Survey

Creators: Polletta, Maria del Carmen; Wilkes, Belinda J.; Siana, Brian; Lonsdale, Carol J.; Kilgard, Roy; Smith, Harding E.; Kim, Dong-Woo; Owen, Frazer; Efstathiou, Andreas; Jarrett, Tom; Stacey, Gordon; Franceschini, Alberto; Rowan-Robinson, Michael; Babbedge, Tom S. R.; Berta, Stefano; Fang, Fan; Farrah, Duncan; Gonzalez-Solares, Eduardo; Morrison, Glenn; Surace, Jason A.; Shupe, Dave L.

Abstract

Using the large multiwavelength data set in the Chandra/SWIRE Survey (0.6 deg^2 in the Lockman Hole), we show evidence for the existence of highly obscured (Compton-thick) AGNs, estimate a lower limit to their surface density, and characterize their multiwavelength properties. Two independent selection methods based on the X-ray and infrared spectral properties are presented. The two selected samples contain (1) five X-ray sources with hard X-ray spectra and column densities ≳ 10^(24) cm^(-2) and (2) 120 infrared sources with red and AGN-dominated infrared SEDs. We estimate a surface density of at least 25 Compton-thick AGNs deg^(-2) detected in the infrared in the Chandra/SWIRE field, of which ~40% show distinct AGN signatures in their optical/near-infrared SEDs, the remaining being dominated by the host galaxy emission. Only ~33% of all Compton-thick AGNs are detected in the X-rays at our depth [F(0.3-8 keV) > 10^(-15) ergs cm^(-2) s^(-1)]. We report the discovery of two sources in our sample of Compton-thick AGNs, SWIRE J104409.95+585224.8 (z = 2.54) and SWIRE J104406.30+583954.1 (z = 2.43), which are the most luminous Compton-thick AGNs at high z currently known. The properties of these two sources are discussed in detail with an analysis of their spectra, SEDs, luminosities, and black hole masses.

Additional Information

© 2006 The American Astronomical Society. Received 2005 September 10; accepted 2005 December 21. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. Based on observations at the Kitt Peak National Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under a cooperative agreement by Associated Universities, Inc. M. P. thanks Alain Omont and Dan Weedman for useful discussions. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407. Support for this work, part of the Spitzer Space Telescope Legacy Science Program, was provided by NASA through an award issued by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract 1407. M. P., B. W., and R. K. are grateful for the financial support of NASA grant G04-5158A (Chandra). B. W. is grateful for the financial support of NASA contract NAS8-39073 (Chandra X-Ray Center). This research makes use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This work is based on observations obtained at the Hale Telescope, Palomar Observatory, as part of a continuing collaboration between the California Institute of Technology, NASA/JPL, and Cornell University. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. Facilities: Spitzer ( IRAC,MIPS), CXO (ACIS)

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