Yan-Chuan Cai, Mark C. Neyrinck, Istvan Szapudi, Shaun Cole, Carlos S. Frenk
We measure the average cold spot on the cosmic microwave background(CMB) produced by voids selected in the SDSS DR7 spectroscopic redshift galaxy catalog, spanning redshifts from 0 to 0.4. Our detection has a significance of ~3sigma based on the variance of random samples, and has an average amplitude of ~3 muK as viewed through a compensated top-hat filter scaled to the radius of each void. This signal, if interpreted as the late-time Integrated Sachs-Wolfe effect, serves as an evidence for the late-time acceleration of the Universe. The detection is achieved by applying the optimal filter size identified from N-body simulations. Two striking features are found by comparing ISW simulations with our detection, 1.) the void profiles traced by halos in our simulations are very similar to those in the data traced by galaxies. 2.) the same filter radius that gives the largest ISW signal in simulations also yields the largest detected signal in the observations. We model the expected ISW signal using voids from N-body simulations in LCDM, selected in the same way as in the observations. The detected signal, however, is many times larger than that from simulations, discrepant at the ~3sigma level. The large cosmic variance of large-scale modes in the gravitational potential can obscure an ISW measurement such as ours. However, we show how this cosmic variance can be effectively reduced by using a compensated top-hat filter for the detection. We test whether a few possible systematic effects could be producing the signal; we find no evidence that they do.
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http://arxiv.org/abs/1301.6136
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