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

• Published in: The Astrophysical journal 2006-11, Vol.652 (1), p.126-135
• Main Authors: Beckmann, V, Soldi, S, Shrader, C. R, Gehrels, N, Produit, N
• Format: Article
• Language: English
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1086/507510

We have compiled a complete extragalactic sample based on 625,000 deg super(2) to a limiting flux of 3 x 10 super(-11) ergs cm super(-2) s super(-1) (67000 deg super(2) to a flux limit of 10 super(-11) ergs cm super(-2) s super(-1)) in the 20-40 keV band with INTEGRAL. We have constructed a detailed exposure map to compensate for effects of nonuniform exposure. The flux-number relation is best described by a power law with a slope of a = 1.66 c 0.11. The integration of the cumulative flux per unit area leads to f sub(20-40 keV) = 2.6 x 10 super(-10) ergs cm super(-2) s super(-1) sr super(-1), which is about 1% of the known 20-40 keV X-ray background. We present the first luminosity function of AGNs 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 double-power-law form with an index of g sub(1) = 0.8 below and g sub(2) = 2.1 above the turnover luminosity of L sub(*) = 2.4 x 10 super(43) ergs s super(-1). The emissivity of all INTEGRAL AGNs per unit volume is W sub(20-40 keV) (> 10 super(41) ergs s super(-1)) = 2.8 x 10 super(38) ergs s super(-1) h super(3) sub(70) Mpc super(-3). 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 ( = 0.022), only limited conclusions can be drawn for the evolution of AGNs in this energy band.