On the signature of z ~ 0.6 superclusters and voids in the integrated sachs-wolfe effect

Abstract

Through a large ensemble of Gaussian realizations and a suite of large-volume N-body simulations, we show that in a standard λ cold dark matter (λCDM) scenario, supervoids and superclusters in the redshift range z ε [0.4, 0.7] should leave a small signature on the Integrated Sachs-Wolfe (ISW) effect of the order of ~2 μK. We perform aperture photometry on Wilkinson Microwave Anisotropy Probe (WMAP) data, centred on such superstructures identified from SDSS luminous red Galaxies data, and find amplitudes at the level of 8-11 μK - thus, confirming the earlier work of Granett et al. If we focus on apertures of the size ~3°. 6, then our realizations indicate that λCDM is discrepant at the level of ~4 σ. However, if we combine all aperture scales considered, ranging from 1°to 20°, then the discrepancy becomes ~2 σ, and it further lowers to ~0.6 σ if only 30 superstructures are considered in the analysis (being compatible with no ISW signatures at 1.3 s in this case). Full-sky ISW maps generated from our N-body simulations show that this discrepancy cannot be alleviated by appealing to Rees-Sciama mechanisms, since their impact on the scales probed by our filters is negligible. We perform a series of tests on the WMAP data for systematics. We check for foreground contaminants and show that the signal does not display the correct dependence on the aperture size expected for a residual foreground tracing the density field. The signal also proves robust against rotation tests of the cosmic microwave background maps, and seems to be spatially associated with the angular positions of the supervoids and superclusters. We explore whether the signal can be explained by the presence of primordial non-Gaussianities of the local type. We show that for models with f localNL = ±100, whilst there is a change in the pattern of temperature anisotropies, all amplitude shifts are well below <1 μK. If primordial non-Gaussianity were to explain the result, then f localNL would need to be several times larger than currently permitted by WMAP constraints. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.