Correlation of the 2-10 keV X-ray background with nearby galaxies

Abstract

Catalogues of several types of extragalactic objects have been cross-correlated with Ginga measurements of the X-ray background intensity. Some of these catalogues give rise to significant signals, meaning that either sources in them or some other sources clustered around them produce a fraction of the X-ray background. The significance of these results has been established using bootstrap and X-ray background simulations. An expression to infer the local X-ray emissivity from the cross-correlation signal is given and applied to two galaxy catalogues (UGC and IRAS) for which the signal is more significant (>95 per cent). Values of ∼ 1039h ergs−1 Mpc−3 are obtained, implying that ≤ 30 per cent of the X-ray background could be produced by a non-evolving population of galaxies.