COMOVING SPACE DENSITY AND OBSCURED FRACTION OF HIGH-REDSHIFT ACTIVE GALACTIC NUCLEI IN THE SUBARU/XMM-NEWTON DEEP SURVEY

Journal Article · Wed Oct 10 04:00:00 EDT 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/758/1/49· OSTI ID:22092082

Hiroi, Kazuo; Ueda, Yoshihiro ^[1]; Akiyama, Masayuki ^[2]

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1. Department of Astronomy, Kyoto University, Oiwake-cho, Sakyo-ku, Kyoto (Japan)
2. Astronomical Institute, Graduate School of Science, Tohoku University, Aramaki, Aoba, Sendai (Japan)

We study the comoving space density of X-ray-selected luminous active galactic nuclei (AGNs) and the obscured AGN fraction at high redshifts (3 < z < 5) in the Subaru/XMM-Newton Deep Survey field. From an X-ray source catalog with high completeness of optical identification thanks to deep optical images, we select a sample of 30 AGNs at z > 3 with intrinsic (de-absorbed and rest-frame 2-10 keV) luminosities of L{sub X} = 10{sup 44-45} erg s{sup -1} detected in the 0.5-2 keV band, consisting of 20 and 10 objects with spectroscopic and photometric redshifts, respectively. Utilizing the 1/V{sub max} method, we confirm that the comoving space density of luminous AGNs decreases with redshift above z > 3. When combined with the Chandra-COSMOS result of Civano et al., the density decline of AGNs with L{sub X} = 10{sup 44-45} erg s{sup -1} is well represented by a power law of (1 + z){sup -6.2{+-}0.9}. We also determine the fraction of X-ray obscured AGNs with N{sub H} > 10{sup 22} cm{sup -2} in the Compton-thin population to be 0.54{sup +0.17}{sub -0.19}, by carefully taking into account observational biases including the effects of photon statistics for each source. This result is consistent with an independent determination of the type-2 AGN fraction based on optical properties, for which the fraction is found to be 0.59 {+-} 0.09. Comparing our result with that obtained in the local universe, we conclude that the obscured fraction of luminous AGNs increases significantly from z = 0 to z > 3 by a factor of 2.5 {+-} 1.1.

• OSTI ID: 22092082
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 758; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ASTRONOMY
ASTROPHYSICS
CATALOGS
DENSITY
GALAXY NUCLEI
KEV RANGE
LUMINOSITY
PHOTOMETRY
RED SHIFT
UNIVERSE
X RADIATION
X-RAY GALAXIES
X-RAY SOURCES