The Hard X-Ray Luminosity Function of High-Redshift (3<z 5) Active Galactic Nuclei

الأصل · EN

We present the hard-band (2-10keV) X-ray luminosity function (HXLF) of 0.5-2keV band selected AGN at high redshift. We have assembled a sample of 141 AGN at 3<z5 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 logLₓ 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 (logLₓ<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>10⁴⁴ergs⁻¹) obscured AGN fraction from z=0 to z>3.