Neelima Sehgal, Graeme Addison, Nick Battaglia, Elia S. Battistelli, J. Richard Bond, Sudeep Das, Mark J. Devlin, Joanna Dunkley, Rolando Dünner, Megan Gralla, Amir Hajian, Mark Halpern, Matthew Hasselfield, Matt Hilton, Adam D. Hincks, Renée Hlozek, John P. Hughes, Arthur Kosowsky, Yen-Ting Lin, Thibaut Louis, Tobias A. Marriage, Danica Marsden, Felipe Menanteau, Kavilan Moodley, Michael D. Niemack, Lyman A. Page, Bruce Partridge, Erik D. Reese, Blake D. Sherwin, Jon Sievers, Cristóbal Sifón, David N. Spergel, Suzanne T. Staggs, Daniel S. Swetz, Eric R. Switzer, Ed Wollack
We present the measured Sunyaev-Zel'dovich (SZ) flux from 474 optically-selected MaxBCG clusters that fall within the Atacama Cosmology Telescope (ACT) Equatorial survey region. The ACT Equatorial region used in this analysis covers 510 square degrees and overlaps Stripe 82 of the Sloan Digital Sky Survey. We also present the measured SZ flux stacked on 52 X-ray-selected MCXC clusters that fall within the ACT Equatorial region and an ACT Southern survey region covering 455 square degrees. We find that the measured SZ flux from the X-ray-selected clusters is consistent with expectations. However, we find that the measured SZ flux from the optically-selected clusters is both significantly lower than expectations and lower than the recovered SZ flux measured by the Planck satellite. Since we find a lower recovered SZ signal than Planck, we investigate the possibility that there is a significant offset between the optically-selected brightest cluster galaxies (BCGs) and the SZ centers, to which ACT is more sensitive due to its finer resolution. Such offsets can arise due to either an intrinsic physical separation between the BCG and the center of the gas concentration or from misidentification of the cluster BCG. We find that the entire discrepancy for both ACT and Planck can be explained by assuming that the BCGs are offset from the SZ maxima with a uniform random distribution between 0 and 1.5 Mpc. In contrast, the physical separation between BCGs and X-ray peaks for an X-ray-selected subsample of MaxBCG clusters shows a much narrower distribution that peaks within 0.2 Mpc. We conclude that while offsets between BCGs and SZ peaks may be an important component in explaining the discrepancy, it is likely that a combination of factors is responsible for the ACT and Planck measurements. (Abridged)
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http://arxiv.org/abs/1205.2369
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