Wednesday, May 03, 2006

Lieu: Soft X-ray cluster excess and SZ effect

EUD seminar by Richard Lieu from U. Alabama in Huntsville. The first half of the talk was a summary of soft X-ray observations of clusters. There are currently no confirmed observations of redshifted OVII so no definite evidence for WHIM in emission. The soft excess in the outer parts of clusters may still be thermal due to low S/N however that in the brighter regions must be non-thermal - possibly due to relativistic electrons accelerated in shocks or perhaps more exotic sources such as neutralino decay. The second and newer work was looking at WMAP data to measure the SZ effect from a sample of 30 bright, nearby clusters. The results are mixed - some clusters are clearly detected at the expected level (Coma), some are ambiguous, and some appear not to be detected at the level predicted by the X-ray data. Summing all 30 clusters and comparing with sets of randomly selected fields finds a net signal consistent with background (driven by the ~1 degree first peak in the power-spectrum). This is difficult to understand but implies some fraction of clusters do not show an SZ signal of the strength expected. Gary Hinshaw of the WMAP team confirmed that they also detect an SZ effect from Coma and that the noise level in Richard's plots is correct.

Keywords: Clusters, WMAP, SZ

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