CORRELATIONS BETWEEN THE COSMIC X-RAY AND MICROWAVE BACKGROUNDS - CONSTRAINTS ON A COSMOLOGICAL CONSTANT

In universes with significant curvature or cosmological constant, cosm ic microwave background (CMB) anisotropies are created very recently v ia the Rees-Sciama or integrated Sachs-Wolfe effects, This causes the CMB anisotropies to become partially correlated with the local matter density (z < 4). We examine the prospects of using the hard (2-10 keV) X-ray background as a probe of the local density and the measured cor relation between the HEAO1 A2 X-ray survey and the 4-year COBE-DMR map to obtain a constraint on the cosmological constant. The 95% confiden ce level upper limit on the cosmological constant is Omega(Lambda) les s than or equal to 0.5, assuming that the observed fluctuations in the X-ray map result entirely from large scale structure. (This would als o imply that the X-rays trace matter with a bias factor of b(x) simila r or equal to 5.6 Omega(m)(0.53).) This bound is weakened considerably if a large portion of the X-ray fluctuations arise from Poisson noise from unresolved sources. For example, if one assumes that the X-ray b ias is b(x) = 2., then the 95% confidence level upper limit is weaker, Omega(Lambda) less than or equal to 0.7. More stringent limits should be attainable with data from the next generation of CMB and X-ray bac kground maps. (C) 1998 Elsevier Science B.V.