Anomalous SZ contribution to three-year WMAP data

We first show that the new Wilkinson Microwave Anisotropy Probe (WMAP) 3-yr data confirm the detection by Myers et al. of an extended SZ signal centred on 606 Abell (ACO)clusters with richness class, R >= 2. Our results also show SZ decrements around APM and 2MASS groups at increased significance than previously detected. We then followthe approach of Lieu, Mittaz & Zhang and compare the stacked WMAP results for the decrement in 31 clusters with ROSAT X-ray profiles where Lieu et al. found on average less SZ decrement in the WMAP 1-yr data than predicted. We confirm that in the 3-yr data these same clusters again show less SZ decrement than the X-ray data predict. We then analysed the WMAP results for the 38 X-ray clusters with OVRO/BIMA measured SZ decrements as presented by Bonamente et al.. We again find that the average decrement is measured to be significantly less (5.5s) than predicted by the Chandra X-ray data. Thus while we confirm the original detection of an extended SZ effect by Myers et al., these X-ray comparisons may now suggest that the central SZ amplitudes detected by WMAP may actually be lower than expected. One possible explanation is that there is contamination of the WMAP SZ signal by radio sources in the clusters but we argue that this appears implausible. We then consider the possibility that the SZ decrement has been lensed away by foreground galaxy groups. Such a model predicts that the SZ decrement should depend on cluster redshift. A reduction in the SZ decrement with redshift is suggested from the ACO cluster sample and also from comparing the samples of Lieu et al. and Bonamente et al.. However, the mass power spectrum would require a far higher amplitude than currently expected if lensing was to explain the SZ deficit in high-redshift clusters.