期刊
ASTROPHYSICAL JOURNAL
卷 741, 期 2, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/741/2/91
关键词
evolution; galaxies: active; surveys; X-rays: galaxies
资金
- NASA [GO7-8136A]
- Blancheflor Boncompagni Ludovisi foundation
- Smithsonian Scholarly Studies
- Alexander von Humboldt Foundation
- ASI/INAF [I/009/10/0, I/088/06]
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(phot) < 3 but with a broad photometric redshift probability distribution, such that z(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((2-10 keV)) > 44.15 erg s(-1)) space density up to z similar to 5 and a fainter luminosity range (43.5 erg s(-1) < log L((2-10 keV)) < 44.15 erg s(-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.
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