A Search for X-Ray Reionization Signatures from Cross-Correlation of Wmap and ROSAT Rass Data

We present an observational search for the possible correlation between cosmic microwave background (CMB) polarization map and soft X-ray background (SXRB) based on the ROSAT All-sky Survey (RASS) archive and WMAP five-year observations. This is motivated by the fact that some of the CMB polarization may arise from the scattering of CMB photons due to the free electrons generated by X-ray heating sources in the epoch of reionization. Detection of such a correlation allows one to study the role of X-ray heating in the process of reionization. However, the cross angular power spectrum of the CMB polarization and SXRB maps constructed from ROSAT RASS and WMAP five-year maps is consistent with no correlation. We attribute this negative detection to both the extremely weak signals and large instrumental noises. While a future search is needed with high sensitivity instruments for both CMB polarization and soft X-ray photons, our current results can still be used as a useful constraint on the effect of X-ray heating in the epoch of reionization.