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Title: THE POPULATION OF HIGH-REDSHIFT ACTIVE GALACTIC NUCLEI IN THE CHANDRA-COSMOS SURVEY

Abstract

We present the high-redshift (3 <z < 5.3) 0.5-2 keV number counts and the 2-10 keV (rest-frame) space density of X-ray-selected active galactic nuclei (AGNs) detected in the Chandra Cosmic Evolution Survey. The sample comprises 81 X-ray-detected sources with available spectroscopic (31) and photometric (50) redshifts plus 20 sources with a formal z{sub phot} < 3 but with a broad photometric redshift probability distribution, such that z{sub phot} + 1{sigma} > 3. Eighty-one sources are selected in the 0.5-2 keV band, fourteen are selected in the 2-10 keV and six in the 0.5-10 keV bands. We sample the high-luminosity (log L{sub (2-10keV)} > 44.15 erg s{sup -1}) space density up to z {approx} 5 and a fainter luminosity range (43.5 erg s{sup -1} < log L{sub (2-10keV)} < 44.15 erg s{sup -1}) than previous studies, up to z = 3.5. We weighted the contribution to the number counts and the space density of the sources with photometric redshift by using their probability of being at z > 3. We find that the space density of high-luminosity AGNs declines exponentially at all the redshifts, confirming the trend observed for optically selected quasars. At lower luminosity, the measured space density is notmore » conclusive, and a larger sample of faint sources is needed. Comparisons with optical luminosity functions and black hole formation models are presented together with prospects for future surveys.« less

Authors:
; ;  [1];  [2]; ; ; ;  [3];  [4]; ; ;  [5];  [6];  [7];  [8];  [9];  [10];  [11];  [12];  [13]
  1. Harvard Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
  2. Max Planck Institut fuer Extraterrestrische Physik Giessenbach strasse 1, D-85748 Garching (Germany)
  3. INAF-Osservatorio Astronomico di Bologna, via Ranzani 1, I-40127 Bologna (Italy)
  4. Max-Planck-Institute for Plasma Physics, Boltzmannstrass 2, Garching D-85748 (Germany)
  5. California Institute of Technology, 1201 East California Boulevard, Pasadena, CA 91125 (United States)
  6. INAF-Osservatorio Astronomico di Roma, via Frascati 33, Monteporzio-Catone (Roma) I-00040 (Italy)
  7. Graduate School of Science and Engineering, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577 (Japan)
  8. Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)
  9. Instituto de Astronomia, Universidad Nacional Autonoma de Mexico-Ensenada, Km. 103 Carretera Tijuana-Ensenada, 22860 Ensenada (Mexico)
  10. ASI Science Data Center, via Galileo Galilei, 00044 Frascati (Italy)
  11. Max-Planck-Institut fuer Astrophysik, Karl-Schwarzschild-Str. 1, D-85748 Garching (Germany)
  12. Institute for the Physics and Mathematics of the Universe (IPMU), University of Tokyo, Kashiwanoha 5-1-5, Kashiwa, Chiba 277-8568 (Japan)
  13. Dipartimento di Astronomia, Universita di Bologna, via Ranzani 1, 40127 Bologna (Italy)
Publication Date:
OSTI Identifier:
21612698
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 741; Journal Issue: 2; Other Information: DOI: 10.1088/0004-637X/741/2/91; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BLACK HOLES; GALACTIC EVOLUTION; GALAXY NUCLEI; LUMINOSITY; QUASARS; RED SHIFT; UNIVERSE; X-RAY GALAXIES; COSMIC RADIO SOURCES; COSMIC RAY SOURCES; COSMIC X-RAY SOURCES; EVOLUTION; GALAXIES; OPTICAL PROPERTIES; PHYSICAL PROPERTIES

Citation Formats

Civano, F., Elvis, M., Hao, H., Brusa, M., Comastri, A., Zamorani, G., Gilli, R., Mignoli, M., Salvato, M., Capak, P., Kakazu, Y., Masters, D., Fiore, F., Ikeda, H., Kartaltepe, J. S., Miyaji, T., Puccetti, S., Shankar, F., Silverman, J., and Vignali, C. THE POPULATION OF HIGH-REDSHIFT ACTIVE GALACTIC NUCLEI IN THE CHANDRA-COSMOS SURVEY. United States: N. p., 2011. Web. doi:10.1088/0004-637X/741/2/91; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
Civano, F., Elvis, M., Hao, H., Brusa, M., Comastri, A., Zamorani, G., Gilli, R., Mignoli, M., Salvato, M., Capak, P., Kakazu, Y., Masters, D., Fiore, F., Ikeda, H., Kartaltepe, J. S., Miyaji, T., Puccetti, S., Shankar, F., Silverman, J., & Vignali, C. THE POPULATION OF HIGH-REDSHIFT ACTIVE GALACTIC NUCLEI IN THE CHANDRA-COSMOS SURVEY. United States. doi:10.1088/0004-637X/741/2/91; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
Civano, F., Elvis, M., Hao, H., Brusa, M., Comastri, A., Zamorani, G., Gilli, R., Mignoli, M., Salvato, M., Capak, P., Kakazu, Y., Masters, D., Fiore, F., Ikeda, H., Kartaltepe, J. S., Miyaji, T., Puccetti, S., Shankar, F., Silverman, J., and Vignali, C. 2011. "THE POPULATION OF HIGH-REDSHIFT ACTIVE GALACTIC NUCLEI IN THE CHANDRA-COSMOS SURVEY". United States. doi:10.1088/0004-637X/741/2/91; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA).
@article{osti_21612698,
title = {THE POPULATION OF HIGH-REDSHIFT ACTIVE GALACTIC NUCLEI IN THE CHANDRA-COSMOS SURVEY},
author = {Civano, F. and Elvis, M. and Hao, H. and Brusa, M. and Comastri, A. and Zamorani, G. and Gilli, R. and Mignoli, M. and Salvato, M. and Capak, P. and Kakazu, Y. and Masters, D. and Fiore, F. and Ikeda, H. and Kartaltepe, J. S. and Miyaji, T. and Puccetti, S. and Shankar, F. and Silverman, J. and Vignali, C.},
abstractNote = {We present the high-redshift (3 <z < 5.3) 0.5-2 keV number counts and the 2-10 keV (rest-frame) space density of X-ray-selected active galactic nuclei (AGNs) detected in the Chandra Cosmic Evolution Survey. The sample comprises 81 X-ray-detected sources with available spectroscopic (31) and photometric (50) redshifts plus 20 sources with a formal z{sub phot} < 3 but with a broad photometric redshift probability distribution, such that z{sub phot} + 1{sigma} > 3. Eighty-one sources are selected in the 0.5-2 keV band, fourteen are selected in the 2-10 keV and six in the 0.5-10 keV bands. We sample the high-luminosity (log L{sub (2-10keV)} > 44.15 erg s{sup -1}) space density up to z {approx} 5 and a fainter luminosity range (43.5 erg s{sup -1} < log L{sub (2-10keV)} < 44.15 erg s{sup -1}) than previous studies, up to z = 3.5. We weighted the contribution to the number counts and the space density of the sources with photometric redshift by using their probability of being at z > 3. We find that the space density of high-luminosity AGNs declines exponentially at all the redshifts, confirming the trend observed for optically selected quasars. At lower luminosity, the measured space density is not conclusive, and a larger sample of faint sources is needed. Comparisons with optical luminosity functions and black hole formation models are presented together with prospects for future surveys.},
doi = {10.1088/0004-637X/741/2/91; COUNTRY OF INPUT: INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)},
journal = {Astrophysical Journal},
number = 2,
volume = 741,
place = {United States},
year = 2011,
month =
}
  • Chandra observations of a complete, flux-limited sample of 38 high-redshift (1 < z < 2), low-frequency-selected (and so unbiased in orientation) 3CRR radio sources are reported. The sample includes 21 quasars (=broad-line radio galaxies) and 17 narrow-line radio galaxies (NLRGs) with matched 178 MHz radio luminosity (log L{sub R}(5 GHz) {approx}44-45). The quasars have high radio core fraction, high X-ray luminosities (log L{sub X} {approx}45-46), and soft X-ray hardness ratios (HR {approx}-0.5) indicating low obscuration. The NLRGs have lower core fraction, lower apparent X-ray luminosities (log L{sub X} {approx}43-45), and mostly hard X-ray hardness ratios (HR >0) indicating obscuration (N{submore » H} {approx}10{sup 22}-10{sup 24} cm{sup -2}). These properties and the correlation between obscuration and radio core fraction are consistent with orientation-dependent obscuration as in unification models. About half the NLRGs have soft X-ray hardness ratios and/or a high [O III] emission line to X-ray luminosity ratio suggesting obscuration by Compton thick (CT) material so that scattered nuclear or extended X-ray emission dominates (as in NGC 1068). The ratios of unobscured to Compton-thin (10{sup 22} cm{sup -2} < N{sub H}(int) <1.5 Multiplication-Sign 10{sup 24} cm{sup -2}) to CT (N{sub H}(int) >1.5 Multiplication-Sign 10{sup 24} cm{sup -2}) is 2.5:1.4:1 in this high-luminosity, radio-selected sample. The obscured fraction is 0.5, higher than is typically reported for active galactic nuclei at comparable luminosities from multi-wavelength surveys (0.1-0.3). Assuming random nuclear orientation, the unobscured half-opening angle of the disk/wind/torus structure is {approx}60 Degree-Sign and the obscuring material covers 30 Degree-Sign , {approx}12 Degree-Sign of which is CT. The multi-wavelength properties reveal that many NLRGs have intrinsic absorption 10-1000 Multiplication-Sign higher than indicated by their X-ray hardness ratios, and their true L{sub X} values are {approx}10-100 Multiplication-Sign larger than the hardness-ratio absorption corrections would indicate.« less
  • In this paper, we release accurate photometric redshifts for 1692 counterparts to Chandra sources in the central square degree of the Cosmic Evolution Survey (COSMOS) field. The availability of a large training set of spectroscopic redshifts that extends to faint magnitudes enabled photometric redshifts comparable to the highest quality results presently available for normal galaxies. We demonstrate that morphologically extended, faint X-ray sources without optical variability are more accurately described by a library of normal galaxies (corrected for emission lines) than by active galactic nucleus (AGN) dominated templates, even if these sources have AGN-like X-ray luminosities. Preselecting the library onmore » the bases of the source properties allowed us to reach an accuracy {sigma}{sub {Delta}z/(1+z{sub s{sub p{sub e{sub c)}}}}}{approx}0.015 with a fraction of outliers of 5.8% for the entire Chandra-COSMOS sample. In addition, we release revised photometric redshifts for the 1735 optical counterparts of the XMM-detected sources over the entire 2 deg{sup 2} of COSMOS. For 248 sources, our updated photometric redshift differs from the previous release by {Delta}z > 0.2. These changes are predominantly due to the inclusion of newly available deep H-band photometry (H{sub AB} = 24 mag). We illustrate once again the importance of a spectroscopic training sample and how an assumption about the nature of a source together, with the number and the depth of the available bands, influences the accuracy of the photometric redshifts determined for AGN. These considerations should be kept in mind when defining the observational strategies of upcoming large surveys targeting AGNs, such as eROSITA at X-ray energies and the Australian Square Kilometre Array Pathfinder Evolutionary Map of the Universe in the radio band.« less
  • Using a physically motivated, model-based active galactic nucleus (AGN) characterization technique, we fit a large sample of X-ray-selected AGNs with known spectroscopic redshifts from the Cosmic Evolution Survey field. We identify accretion disks in the spectral energy distributions of broad- and narrow-line AGNs, and infer the presence or absence of host galaxy light in the SEDs. Based on infrared and UV excess AGN selection techniques, our method involves fitting a given SED with a model consisting of three components: infrared power-law emission, optical-UV accretion disk emission, and host galaxy emission. Each component can be varied in relative contribution, and amore » reduced chi-square minimization routine is used to determine the optimum parameters for each object. Using this technique, both broad- and narrow-line AGNs fall within well-defined and plausible bounds on the physical parameters of the model, allowing trends with luminosity and redshift to be determined. In particular, based on our sample of spectroscopically confirmed AGNs, we find that approximately 95% of the broad-line AGNs and 50% of the narrow-line AGNs in our sample show evidence of an accretion disk, with maximum disk temperatures ranging from 1 to 10 eV. Because this fitting technique relies only on photometry, we hope to apply it in future work to the characterization and eventually the selection of fainter AGNs than are accessible in wide-field spectroscopic surveys, and thus probe a population of less luminous and/or higher redshift objects without prior redshift or X-ray data. With the abundant availability of photometric data from large surveys, the ultimate goal is to use this technique to create large samples that will complement and complete AGN catalogs selected by X-ray emission alone.« less
  • The Wide-field Infrared Survey Explorer (WISE) is an extremely capable and efficient black hole finder. We present a simple mid-infrared color criterion, W1 - W2 {>=} 0.8 (i.e., [3.4]-[4.6] {>=}0.8, Vega), which identifies 61.9 {+-} 5.4 active galactic nucleus (AGN) candidates per deg{sup 2} to a depth of W2 {approx} 15.0. This implies a much larger census of luminous AGNs than found by typical wide-area surveys, attributable to the fact that mid-infrared selection identifies both unobscured (type 1) and obscured (type 2) AGNs. Optical and soft X-ray surveys alone are highly biased toward only unobscured AGNs, while this simple WISEmore » selection likely identifies even heavily obscured, Compton-thick AGNs. Using deep, public data in the COSMOS field, we explore the properties of WISE-selected AGN candidates. At the mid-infrared depth considered, 160 {mu}Jy at 4.6 {mu}m, this simple criterion identifies 78% of Spitzer mid-infrared AGN candidates according to the criteria of Stern et al. and the reliability is 95%. We explore the demographics, multiwavelength properties and redshift distribution of WISE-selected AGN candidates in the COSMOS field.« less
  • 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 datamore » 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.« less