Top: Evolution of the number density of X‐ray AGNs in three bins of luminosity (in units of ergs s⁻¹, in the band 2–10 keV): ﹩43< \mathrm{log}\,L_{\mathrm{X}\,}< 44﹩ (dotted line), ﹩44< \mathrm{log}\,L_{\mathrm{X}\,}< 44.5﹩ (solid line), and ﹩44.5< \mathrm{log}\,L_{\mathrm{X}\,}﹩ (dashed line). The data for the above luminosity bins (squares, triangles, and circles, respectively) are taken from Fiore et al. (2003). Bottom: Evolution of the X‐ray luminosity density for the same luminosity bins.