The Sunyaev‐Zel’dovich Effect in a Sample of 31 Clusters: A Comparison between the X‐Ray Predicted andWMAPObserved Cosmic Microwave Background Temperature Decrement

The WMAP Q, V, and W band radial profiles of temperature deviation of thecosmic microwave background (CMB) were constructed for a sample of 31 randomlyselected nearby clusters of galaxies in directions of Galactic latitude $|b| >$30$^o$. The profiles were compared in detail with the expected CMBSunyaev-Zel'dovich effect (SZE) caused by these clusters, with the hot gasproperties of each cluster inferred observationally by applying gastemperatures as measured by ASCA to isothermal $\beta$ models of the ROSATX-ray surface brightness profiles, and with the WMAP point spread functionfully taken into consideration. After co-adding the 31 cluster field, itappears that WMAP detected the SZE in all three bands. Quantitatively, however,the observed SZE only accounts for about 1/4 of the expected decrement. Thediscrepancy represents too much unexplained extra flux: in the W band, thedetected SZE corresponds on average to 5.6 times less X-ray gas mass within a10 arcmin radius than the mass value given by the ROSAT $\beta$ model. Weexamined critically how the X-ray prediction of the SZE may depend on ouruncertainties in the density and temperature of the hot intracluster plasma,and emission by cluster radio sources. Although our comparison between thedetected and expected SZE levels is subject to a margin of error, the factremains that the average observed SZE depth and profile are consistent withthose of the primary CMB anisotropy, i.e. in principle the average WMAPtemperature decrement among the 31 rich clusters is too shallow to accomodateany extra effect like the SZE. A unique aspect of this SZE investigation isthat because all the data being analyzed are in the public domain, our work isreadily open to the scrutiny of others.Comment: ApJ v648, p176 (2006). This is the final version to appear on Sept. 1s