Recently , we presented evidence for a cross-correlation of the WMAP satellite map of the cosmic microwave background ( CMB ) and the HEAO 1 satellite map of the hard X-ray background ( XRB ) with a dimensionless amplitude of 0.14 \pm 0.05 normalized to the product of the rms fluctuations of the CMB and XRB ( Boughn & Crittenden , 2004 ) .
Such a correlation is expected in a universe dominated by a cosmological constant via the integrated Sachs-Wolfe ( ISW ) effect and the level of the correlation observed is consistent with that predicted by the currently favored Lambda cold dark matter ( \Lambda CDM ) model of the universe .
Since this offers independent confirmation of the cosmological model , it is important to verify the origin of the correlation .
Here we explore in detail some possible foreground sources of the correlation .
The present evidence all supports an ISW origin .