Cosmological Evolution of the Hard X-Ray Active Galactic Nucleus Luminosity Function and the Origin of the Hard X-Ray Background

We investigate the cosmological evolution of the hard X-ray luminosity function (HXLF) of active galactic nuclei (AGNs) in the 2-10 keV luminosity range of 1041.5-1046.5 ergs s-1 as a function of redshift up to 3. From a combination of surveys conducted at photon energies above 2 keV with HEAO 1, ASCA, and Chandra, we construct a highly complete (>96%) sample consisting of 247 AGNs over the wide flux range of 10-10 to 3.8 × 10-15 ergs cm-2 s-1 (2-10 keV). For our purpose, we develop an extensive method of calculating the intrinsic (before absorption) HXLF and the absorption (NH) function. This utilizes the maximum likelihood method, fully correcting for observational biases with consideration of the X-ray spectrum of each source. We find that (1) the fraction of X-ray absorbed AGNs decreases with the intrinsic luminosity and (2) the evolution of the HXLF of all AGNs (including both type I and type II AGNs) is best described with a luminosity-dependent density evolution (LDDE) where the cutoff redshift increases with the luminosity. Our results directly constrain the evolution of AGNs that produce a major part of the hard X-ray background, thus solving its origin quantitatively. A combination of the HXLF and the NH function enables us to construct a purely observation-based population synthesis model. We present basic consequences of this model and discuss the contribution of Compton-thick AGNs to the rest of the hard X-ray background.

[1]  B. Boyle,et al.  The clustering of QSOs at low redshift , 1993 .

[2]  Chris Done,et al.  The Average X-ray/Gamma-ray Spectra of Seyfert Galaxies from Ginga and OSSE , 1995 .

[3]  Ralf Bender,et al.  The Demography of massive dark objects in galaxy centers , 1997, astro-ph/9708072.

[4]  M. S. Oey,et al.  THE EINSTEIN DATABASE OF IPC X-RAY OBSERVATIONS OF OPTICALLY SELECTED AND RADIO-SELECTED QUASARS .1. , 1994 .

[5]  Y. Ishisaki,et al.  ASCA Observation of Unusually X-Ray-Hard Radio-Quiet QSO Kaz102 , 2003, astro-ph/0302430.

[6]  Collision-induced galaxy formation: semi-analytical model and multiwavelength predictions , 2002, astro-ph/0210030.

[7]  P. Hewett,et al.  The Soft X-Ray Properties of a Large Optical QSO Sample: ROSAT Observations of the Large Bright Quasar Survey , 1995 .

[8]  G. Steigman.  The cosmic X-ray background , 1976, Nature.

[9]  D. M. Alexander,et al.  Optical and Infrared Properties of the 2 Ms Chandra Deep Field North X-Ray Sources , 2003, astro-ph/0306212.

[10]  George H. Rieke,et al.  Low-luminosity and obscured seyfert nuclei in nearby galaxies , 1995 .

[11]  T. Miyaji,et al.  Evolution of AGNs and a model of the X-ray back-ground , 2000 .

[12]  R. Giacconi,et al.  The ROSAT Deep Survey - VI. X-ray sources and Optical identifications of the Ultra Deep Survey , 2001 .

[13]  A. C. Fabian,et al.  Fitting the spectrum of the X-ray background: the effects of high-metallicity absorption , 1999 .

[14]  A. Zdziarski,et al.  Angle-dependent Compton reflection of X-rays and gamma-rays , 1995 .

[15]  T. Tsuru,et al.  A population of faint galaxies that contribute to the cosmic X-ray background , 1998, Nature.

[16]  A. Lawrence,et al.  Obscuration and the various kinds of Seyfert galaxies , 1982 .

[17]  T. J. Turner,et al.  The EXOSAT spectral survey of AGN , 1989 .

[18]  G. Hasinger,et al.  Testing current synthesis models of the X-ray background , 2000, astro-ph/0011341.

[19]  K. Wood,et al.  The HEAO A-1 X-Ray Source Catalog (Wood+, 1984) , 1984 .

[20]  E. al.,et al.  Composite Quasar Spectra from the Sloan Digital Sky Survey , 2001, astro-ph/0105231.

[21]  B. Boyle,et al.  ASCA observations of deep ROSAT fields — II. The 2–10 keV AGN luminosity function , 1998 .

[22]  W. Brandt,et al.  The Redshift Evolution of the 2-8 keV X-Ray Luminosity Function , 2003, astro-ph/0301231.

[23]  J. Matteson,et al.  The Spectrum of Diffuse Cosmic Hard X-Rays Measured with HEAO 1 , 1999, astro-ph/9903492.

[24]  T. Miyaji,et al.  On the relationship between galaxy formation and quasar evolution , 1999, astro-ph/9909290.

[25]  Hagai Netzer,et al.  ASCA Observations of Seyfert 1 Galaxies. III. The Evidence for Absorption and Emission Due to Photoionized Gas , 1997, astro-ph/9708046.

[26]  T. Takahashi,et al.  log N-log S Relations and Spectral Properties of Sources from the ASCA Large Sky Survey: Their Implications for the Origin of the Cosmic X-Ray Background (CXB) , 1999, astro-ph/9901101.

[27]  The BeppoSAX High-Energy Large-Area Survey. V. The Nature of the Hard X-Ray Source Population and Its Evolution , 2001, astro-ph/0112455.

[28]  Toru Yamada,et al.  Optical Identification of the ASCA Medium Sensitivity Survey in the Northern Sky: Nature of Hard X-Ray-Selected Luminous Active Galactic Nuclei , 2003, astro-ph/0307164.

[29]  Wolfgang Voges,et al.  Optical Identification of the ASCA Large Sky Survey , 2000 .

[30]  G. Kauffmann,et al.  A unified model for the evolution of galaxies and quasars , 1999, astro-ph/9906493.

[31]  T. J. Turner,et al.  ASCA observations of Seyfert 1 galaxies: I. Data Analysis, Imaging and Timing , 1996 .

[32]  European Southern Observatory,et al.  XMM-Newton observation of the Lockman Hole - II. Spectral analysis , 2002, astro-ph/0207166.

[33]  G. Kriss,et al.  X-ray properties of quasars and results from a deep X-ray survey of optically selected objects , 1985 .

[34]  G. Hasinger,et al.  ASCA Deep Survey in the Lockman Hole Field , 2001 .

[35]  J. Turner.  X‐ray spectra of a large sample of quasars with ASCA , 2000, astro-ph/0003080.

[36]  Scott M. Croom,et al.  The 2dF QSO Redshift Survey — I. The optical luminosity function of quasi-stellar objects , 2000 .

[37]  X. Barcons,et al.  On the intensity of the extragalactic X-ray background , 2000 .

[38]  W. N. Brandt,et al.  X-Ray, Optical, and Infrared Imaging and Spectral Properties of the 1 Ms Chandra Deep Field North Sources , 2002 .

[39]  N. Gehrels.  Confidence limits for small numbers of events in astrophysical data , 1986 .

[40]  K. Makishima,et al.  The ASCA Medium-Sensitivity Survey (The GIS Catalog Project): Source Counts and Evidence for Emerging Population of Hard Sources , 1999, astro-ph/9908128.

[41]  A. C. Fabian,et al.  The unified Seyfert scheme and the origin of the cosmic X-ray background , 1994 .

[42]  H. Tananbaum,et al.  X-Ray properties of optically selected QSOs , 1986 .

[43]  Kirpal Nandra,et al.  ASCA Observations of Type 2 Seyfert Galaxies. I. Data Analysis Results , 1997 .

[44]  A. Comastri,et al.  The 2-10 keV luminosity as a Star Formation Rate indicator , 2003 .

[45]  J. Dickey,et al.  H I in the Galaxy , 1990 .

[46]  A. Franceschini,et al.  Origin of the X-ray background and AGN unification: new perspectives , 2002, astro-ph/0205529.

[47]  B. Boyle,et al.  A deep ROSAT survey - I. The QSO X-ray luminosity function. , 1993 .

[48]  Peter J. Serlemitsos,et al.  Complete x-ray sample of the high-latitude (Vertical BarbVertical Bar>20/sup 0/) sky from HEAO 1 A-2: Log N-log S and luminosity functions , 1982 .

[49]  Masaru Matsuoka,et al.  New X-ray spectral observations of NGC 4151 with ASCA , 1994 .

[50]  Xavier Barcons,et al.  The Origin of the X-Ray Background , 1984 .

[51]  Roberto Gilmozzi,et al.  Chandra Deep Field South: The 1 Ms Catalog , 2002 .

[52]  X. Barcons,et al.  XMM-Newton observation of the lockman hole. I. The X-ray data , 2000, astro-ph/0011271.

[53]  R. Della Ceca,et al.  The properties of X-ray-selected active galactic nuclei. I - Luminosity function, cosmological evolution, and contribution to the diffuse X-ray background , 1991 .

[54]  Richard E. Rothschild,et al.  The diffuse X-ray background spectrum from 3 to 50 keV. , 1980 .

[55]  M. J. Page,et al.  The evolution of QSOs derived from soft X-ray surveys , 1997 .

[56]  Barry E. Burke,et al.  An abuttable CCD imager for visible and X-ray focal plane arrays , 1991 .

[57]  Juri Poutanen,et al.  Observations of Seyfert Galaxies by OSSE and Parameters of Their X-Ray/Gamma-Ray Sources , 2000 .

[58]  L. Kewley,et al.  The Chandra Deep Field-South: The 1 Million Second Exposure , 2001, astro-ph/0110452.

[59]  D. M. Alexander,et al.  The Chandra Deep Field North Survey. V. 1 Ms Source Catalogs , 2001, astro-ph/0108404.

[60]  R. Mushotzky,et al.  THE NATURE OF THE HARD X-RAY BACKGROUND SOURCES: OPTICAL, NEAR-INFRARED, SUBMILLIMETER, AND RADIO PROPERTIES , 2000, astro-ph/0007175.

[61]  M. Turner,et al.  Ginga observations of the X-ray spectra of quasars , 1997 .

[62]  H. Kaneda,et al.  The Gas Imaging Spectrometer on Board ASCA , 1996 .

[63]  E. Palazzi,et al.  BeppoSAX/PDS identification of the true counterpart of the Piccinotti source H0917-074 , 2002, astro-ph/0208395.

[64]  G. Fasano,et al.  A multidimensional version of the Kolmogorov–Smirnov test , 1987 .

[65]  A. C. Fabian,et al.  X-ray background synthesis: the infrared connection , 2002, astro-ph/0211129.

[66]  Y. Terashima,et al.  CHANDRA SNAPSHOT OBSERVATIONS OF LOW-LUMINOSITY AGNS WITHA COMPACT RADIO SOURCE , 2002 .

[67]  T. Miyaji,et al.  Soft X-ray AGN Luminosity Function from ROSAT Surveys II. Table of the binned Soft X-ray Luminosity Function , 2001, astro-ph/0101279.

[68]  X-ray emission from radio-quiet quasars in the SDSS Early Data Release. The alpha_ox dependence upon UV luminosity , 2002, astro-ph/0211125.

[69]  U. Hawaii,et al.  X-ray QSO evolution from a very deep ROSAT survey , 1996, astro-ph/9610124.

[70]  Kouji Ohta,et al.  A Candidate of a Type 2 Quasi-stellar Object at z = 0.9: Large X-Ray Absorption with a Strong Broad Hα Emission Line , 2001, astro-ph/0111037.

[71]  R. Maiolino,et al.  The Distribution of Absorbing Column Densities among Seyfert 2 Galaxies , 1999, astro-ph/9902377.

[72]  N. Yamasaki,et al.  Study of the X-Ray Background Spectrum and its Large-Scale Fluctuation with ASCA , 2002, astro-ph/0204224.

[73]  K. Nandra,et al.  GINGA observations of the X-ray spectra of Seyfert galaxies. , 1994 .