Comparison of COBE DMR and ROSAT All-Sky Survey data
  Statistical comparisons of microwave maps in the GHz range and X-ray maps at around 1 keV are an interesting probe to constrain different astrophysical phenomena. Possible correlations on various angular scales and with different frequency (energy) dependences, although not expected at present day experimental sensitivity, could in principle be due to Galactic emission/absorption, the Sunyaev-Zel'dovich effect, the Integrated Sachs-Wolfe effect in cosmological models with a cosmological constant or low density, or X-ray luminous radio sources such as radio-loud AGNs. I report on work cross-correlating the COBE DMR and ROSAT All-Sky Survey in a selected area of the sky. This area (+40 deg < b, 70 deg < l < 250 deg) is the best presently available data set probing the medium-hard extragalactic X-ray background around 1 keV. No significant correlation on astrophysically relevant scales has been found in this analysis, but it will be possible to infer constraints from the limits. 
Ruediger Kneissl (MPA, Garching)