The SZ effect contribution to WMAP: A Cross-Correlation between WMAP and ROSAT

We cross-correlate WMAP and ROSAT and look for common features in both data sets. We detect a common structure which shows up clearly in the cross-power spectrum of the cross-correlation. This structure has a coherence length of ≈ 2◦ and its frequency dependence follows the expected SZ effect frequency dependence. Assuming that this structure is due to galaxy clusters, we compute the expected cross-power spectrum for a variety of models and compare them with the expected power spectrum. From these models, we predict the level of contamination of the SZ effect on the power spectrum of the CMB. This contribution is found to be negligible for WMAP and is expected to be very small in experiments like ACBAR or CBI, but can be important for future high resolution experiments. We also discuss possible sources of systematic errors.