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

The Largest X-ray Selected Sample of z>3 AGNs: C-COSMOS & ChaMP