The Hard X-ray 20-40 keV AGN Luminosity Function

We have compiled a complete extragalactic sample based on ∼ 25, 000 deg to a limiting flux of 3 × 10 ergs cm s (∼ 7, 000 deg to a flux limit of 10 ergs cm s) in the 20 – 40 keV band with INTEGRAL. We have constructed a detailed exposure map to compensate for effects of non-uniform exposure. The flux-number relation is best described by a power-law with a slope of α = 1.66 ± 0.11. The integration of the cumulative flux per unit area leads to f20−40 keV = 2.6 × 10 −10 ergs cm s sr, which is about 1% of the known 20− 40 keV X-ray background. We present the first luminosity function of AGN in the 20–40 keV energy range, based on 38 extragalactic objects detected by the imager IBIS/ISGRI on-board INTEGRAL. The luminosity function shows a smoothly connected two power-law form, with an index of γ1 = 0.8 below, and γ2 = 2.1 above the turn-over luminosity of L∗ = 2.4 × 10 43 ergs s. The emissivity of all INTEGRAL AGNs per unit volume is W20−40 keV(> 10 41 ergs s) = 2.8 × 10 ergs s h70 Mpc . These results are consistent with those derived in the 2− 20 keV energy band and do not show a significant contribution by Compton-thick objects. Because the sample used in this study is truly local (z̄ = 0.022), only limited conclusions can be drawn for the evolution of AGNs in this energy band. Subject headings: galaxies: active — gamma rays: observations — X-rays: galaxies — surveys — galaxies: