Space density of AGN in the CDFN in two redshift bins (2 < z < 3, left, and 3 < z < 4, right) and two luminosity bins (10⁴³ < L_{2.0 − 8.0keV} < 10⁴⁴, and 10⁴⁴ < L_{2.0 − 8.0keV} < 10⁴⁵), without correction applied for optical non-detections. Open symbols are based on the sources in the CDFN – GOODS – MOIRCS area with a redshift determination in Barger et al. (2003a) and Trouille et al. (2008) and filled symbols are based on the combination of those sources with those of Table 1. The solid and dashed lines represent the best-fit mod-PLE and LDDE models respectively (see Silverman et al. 2008).