The large-scale bias of the hard X-ray background

Recent deep X-ray surveys combined with spectroscopic identification of the sources have allowed the determination of the rest-frame 2-8 keV luminosity as a function of redshift. In addition, an analysis of the HEAO 1 A-2 2-10 keV full-sky map of the X-ray background reveals clustering on the scale of several degrees. Combining these two results in the context of the currently favored LambdaCDM cosmological model implies an average X-ray bias factor b(X) of b(X)(2)=1.12+/-0.33, i.e., b(X)=1.06+/-0.16. These error estimates include only statistical error; the systematic error sources, while comparable, appear to be subdominant. This result is in contrast to the large biases of some previous estimates and is more in line with current estimates of the optical bias of L-* galaxies.