We present results from an analysis of the largest high-redshift ( z > 3 ) X-ray-selected active galactic nucleus ( AGN ) sample to date , combining the Chandra C-COSMOS and ChaMP surveys and doubling the previous samples .
The sample comprises 209 X-ray-detected AGN , over a wide range of rest frame 2-10 keV luminosities log L _ { X } = 43.3 - 46.0 ~ { } { erg~ { } s ^ { -1 } } .
X-ray hardness rates show that \sim 39 % of the sources are highly obscured , N _ { H } > 10 ^ { 22 } { cm ^ { -2 } } , in agreement with the \sim 37 % of type-2 AGN found in our sample based on their optical classification .
For \sim 26 % of objects have mismatched optical and X-ray classifications .
Using the 1 / V _ { max } method , we confirm that the comoving space density of all luminosity ranges of AGNs decreases with redshift above z > 3 and up to z \sim 7 .
With a significant sample of AGN ( N = 27 ) at z > 4 , it is found that both source number counts in the 0.5 -2 keV band and comoving space density are consistent with the expectation of a luminosity dependent density evolution ( LDDE ) model at all redshifts , while they exclude the luminosity and density evolution ( LADE ) model .
The measured comoving space density of type-1 and type-2 AGN shows a constant ratio between the two types at z > 3 .
Our results for both AGN types at these redshifts are consistent with the expectations of LDDE model .