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R. Lieu, J. Mittaz (University of Alabama, Huntsville), S.-N. Zhang (Tsinghua University, Beijing)
The WMAP Q, V, and W band radial profiles of temperature deviation of the cosmic microwave background (CMB) were constructed for a sample of 31 randomly selected nearby clusters of galaxies in directions of Galactic latitude |b| > 30o. The profiles were compared in detail with the expected CMB Sunyaev-Zel'dovich effect (SZE) caused by these clusters, with the hot gas properties of each cluster obtained directly from X-ray observations, and with the WMAP point spread function fully taken into consideration. While the WMAP profiles of some clusters do exhibit the SZE, the phenomenon is also noted to be weak or absent from other clusters. A reliable overall assessment can be made using the combined (co-added) datasets of all 31 clusters, because (a) any remaining systematic uncertainties are low, and (b) the data are extremely clean (i.e. free from foreground contaminants). Both (a) and (b) are facts which we established by examining hundreds of random fields. The verdict from the 31 co-added cluster fields is that the observed SZE only accounts for about 1/4 of the expected decrement. The discrepancy represents too much extra flux for optically thin intracluster thermal emission to be the cause. Radio sources (discrete or halo) are also excluded because they have negative sloping spectra which are inconsistent with the ratio of the signals in different WMAP filters. A resolution of this discrepancy between predicted and observed decrements have potentially extreme ramifications for our interpretation of the CMB. One is forced to conclude that either the CMB is non-cosmological, or there are issues with the WMAP data itself which must be taken into account when interpreting the CMB emission.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.