26 April 2012
26 April 2012
Speaker: James Bartlett (U. Paris Diderot)
Title:Galaxy Clusters: What We Are Learning From Planck
Abstract:The Planck satellite is furnishing a fresh perspective on galaxy clusters through its all-sky survey via the Sunyaev-Zeldovich (SZ) effect, a distinctive spectral distortion of the cosmic microwave background generated by the hot intra-cluster medium This is, in fact, the first all-sky cluster survey in two decades - since the X-ray survey by the ROSAT satellite in the early 1990s. Reaching deeper in redshift Planck is extending the volume of all-sky cluster catalogs and finding the most massive bound systems in the universe. First cluster results from Planck were published in 2011 (Planck Early Results), including an Early SZ catalog (ESZ) of 189 of the highest significance clusters, follow-up observations with XMM-Newton and statistical studies of large samples of X-ray and optical clusters. Of particular note are these statistical studies, enabled by Planck's all-sky coverage, that allow us to link the X-ray, SZ and optical properties of the cluster population through so-called scaling laws. As a surprise result, we found that the SZ signal from the Sloan maxBCG cluster catalog was much lower than predicted based on simple X-ray cluster models and published weak-lensing masses. I will describe the Planck survey, and review the Planck early results on clusters and discuss their implications, including ideas recently proposed by various authors to explain the Planck-maxBCG result. Such studies are pushing galaxy cluster science to more sophisticated and accurate modeling.