Weike Xiao, Chen Chen, Bin Zhang, Yongfeng Wu, Mi Dai
Galaxy clusters are the most massive objects in the universe, and they comprise a high temperature intracluster medium of about $10^7$K, believed to offer a main foreground effect for the CMB data with thermal Sunyaev-Zel'dovich (SZ) effect. This assumption has been confirmed with SZ signal detection in hundreds of clusters, but comparing with the huge numbers of clusters within optical selected samples from SDSS data, this only accounts for a few percent. Here we introduce a model-independent new method to confirm the assumption that galaxy clusters offer the thermal SZ signal as their main foreground effect. For the WMAP 7year data, we classified data pixels as "to be" or "not to be" affected by the sample clusters, with a parameter of its nearest neighbor cluster's angular distance. By comparing the statistical results of these two kinds of pixels, we can see how the sample clusters affect the CMB data directly. We find that Planck-ESZ sample and the Xray samples($\sim10^2$ clusters) can lead to obvious temperature depression in WMAP 7year data, this confirms the SZ effect prediction. However, each optical selected sample ($> 10^4$ clusters), shows an opposite result: the mean temperature rises to about 10 uK. The unexpected qualitative scenario implies that the main foreground effect of most clusters is NOT always the expected SZ effect. This is maybe the reason why the SZ signal detection result is lower than what is expected by the model.
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http://arxiv.org/abs/1211.6515
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