Astronomy and Astrophysics, volume 462, 57-66 (2007/1-4)
Hard X-ray luminosity function and absorption distribution of nearby AGN: INTEGRAL all-sky survey.
SAZONOV S., REVNIVTSEV M., KRIVONOS R., CHURAZOV E. and SUNYAEV R.
Abstract (from CDS):
We study the hard X-ray luminosity function and absorption distribution of local (z≲0.1) active galactic nuclei (AGN) and discuss the implications for AGN cosmological evolution and for the cosmic X-ray background (CXB). 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 (>5σ) 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 |b|>5°, where the survey's identification completeness is ∼93%, which we use for calculating the AGN luminosity function and X-ray absorption distribution. In broad agreement with previous studies, we find that the fraction fa of obscured (logNH>22) objects is much higher (∼70%) among the low-luminosity AGN (Lhx<1043.6erg/s) than among the high-luminosity ones (Lhx>1043.6 erg/s), fa∼25%, where Lhx is the luminosity in the 17-60keV 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 ∼1040-1041erg/s, 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<logLhx<45.5 with a characteristic luminosity of logL*=43.40±0.28. The estimated local luminosity density due to AGN with logLhx>40 is (1.4±0.3)x1039erg/s/Mpc3 (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 Lhx/L*(z) ratio) has not changed significantly since z∼1.5, while the AGN luminosity function has experienced pure luminosity evolution.