The hard X-ray luminosity function of high-redshift (3 < z ≲ 5) active galactic nuclei

F. Vito, R. Gilli, C. Vignali, A. Comastri, M. Brusa, N. Cappelluti, K. Iwasawa

Research output: Contribution to journalArticlepeer-review

64 Scopus citations


We present the hard-band (2-10 keV) X-ray luminosity function (HXLF) of 0.5-2 keV band selected active galactic nuclei (AGN) at high redshift. We have assembled a sample of 141 AGN at 3 < z ≲ 5 from X-ray surveys of different size and depth, in order to sample different regions in the LX - z plane. The HXLF is fitted in the range log LX ~ 43-45 with standard analytical evolutionary models through a maximum likelihood procedure. The evolution of the HXLF is well described by a pure density evolution, with the AGN space density declining by a factor of ~10 from z = 3 to 5. A luminosity-dependent density evolution model, which, normally, best represents the HXLF evolution at lower redshift, is also consistent with the data, but a larger sample of low-luminosity (log LX < 44), high-redshift AGN is necessary to constrain this model. We also estimated the intrinsic fraction of AGN obscured by a column density logNH ≥ 23 to be 0.54 ± 0.05, with no strong dependence on luminosity. This fraction is higher than the value in the Local Universe, suggesting an evolution of the luminous (LX > 1044 erg s-1) obscured AGN fraction from z = 0 to z > 3.

Original languageEnglish (US)
Pages (from-to)3557-3574
Number of pages18
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
StatePublished - Sep 29 2014
Externally publishedYes


  • Galaxies: active
  • Methods: data analysis
  • Surveys
  • X-rays: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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