The Cosmic X-ray Background -- IRAS galaxy Correlation and the Local X-ray Volume Emissivity

Abstract

We have cross-correlated the galaxies from the IRAS 2 Jy redshift survey sample and the 0.7 Jy projected sample with the all-sky cosmic X-ray background (CXB) map obtained from the HEAO-1 A2 experiment. We have developed a formulation to model the cross-correlation between CXB surface brightness and galaxy counts. This includes the effects of source clustering and the X-ray -- far infrared luminosity correlation. Using an X-ray flux limited sample of AGNs, which has IRAS 60 $\mu m$ measurements, we have estimated the contribution of the AGN component to the observed CXB -- IRAS galaxy count correlations in order to see whether there is an excess component, i.e. contribution from low X-ray luminosity sources. We have applied both the analytical approach and Monte-Carlo simulations for the estimations. Our estimate of the local X-ray volume emissivity in the 2 -- 10 keV band is consistent with the value expected from the luminosity function of AGNs alone and the contribution to the local volume emissivity from lower-luminosity sources is small.