CROSS-CORRELATION OF THE X-RAY-BACKGROUND WITH NEARBY GALAXIES

We have cross-correlated the diffuse 2-10 keV X-ray surface brightness (using the HEAO 1 A-2 data) with the galaxy surface density from the diameter-limited UGC and the ESO catalog. Although the galaxies are nearby (z < 0.03) and sample only a small fraction of the volume believed to produce the X-ray background, we present a statistically significant correlation. The "zero-lag" (for 17 square degree cells) cross-correlation and associated 1-sigma interval is W triple-overdot xg = (3 +/- 1) x 10(-3). We estimate the volume X-ray emissivity of the local universe, rho-x = (2.8 +/- 1.0) x 10(38) ergs s-1 Mpc-3, which implies that unevolved populations of X-ray sources correlated with present-epoch galaxies can contribute only 13% +/- 5% of the cosmic X-ray background.