Hard X-ray luminosity function and absorption distribution of nearby AGN: INTEGRAL all-sky survey

Aims. We study the hard X-ray luminosity function and absorption distribution of local (z less than or similar to 0.1) active galactic nuclei (AGN) and discuss the implications for AGN cosmological evolution and for the cosmic X-ray background (CXB). Methods. We use the INTEGRAL all-sky hard X-ray survey to perform a statistical study of a representative sample of nearby AGN. Our entire all-sky sample consists of 127 AGN, of which 91 are confidently detected (> 5 sigma) on the time-averaged map obtained with the IBIS/ISGRI instrument and 36 are detected only during single observations. Among the former there are 66 non-blazar AGN located at vertical bar b vertical bar > 5 degrees, where the survey's identification completeness is similar to 93%, which we use for calculating the AGN luminosity function and X-ray absorption distribution. Results. In broad agreement with previous studies, we find that the fraction fa of obscured (log N-H > 22) objects is much higher (similar to 70%) among the low-luminosity AGN (L-hx < 10(43.6) erg s(-1)) than among the high-luminosity ones ( Lhx > 1043.6 erg s(-1)), f(a) similar to 25%, where Lhx is the luminosity in the 17-60 keV energy band. We also find that locally the fraction of Compton-thick AGN is less than 20% unless there is a significant population of AGN that are so strongly obscured that their observed hard X-ray luminosities fall below similar to 10(40) - 10(41) erg s(-1), the effective limit of our survey. The constructed hard X-ray luminosity function has a canonical, smoothly broken power-law shape in the range 40 < log L-hx < 45.5 with a characteristic luminosity of log L-* = 43.40 +/- 0.28. The estimated local luminosity density due to AGN with log L-hx > 40 is (1.4 +/- 0.3) x 10(39) erg s(-1) Mpc(-3) (17 - 60 keV). We demonstrate that the spectral shape and amplitude of the CXB are consistent with the simple scenario in which the NH distribution of AGN ( for a given L-hx/L-*(z) ratio) has not changed significantly since z similar to 1.5, while the AGN luminosity function has experienced pure luminosity evolution.