On the signature of $z\sim 0.6$ superclusters and voids in the Integrated Sachs-Wolfe effect

TL;DR

This study investigates the ISW effect signatures of supervoids and superclusters at redshift 0.4-0.7, finding a significant discrepancy between observed signals and LCDM predictions, and testing various systematic and primordial non-Gaussianity explanations.

Contribution

The paper provides a detailed analysis of the ISW effect from superstructures using simulations and WMAP data, highlighting a persistent discrepancy with LCDM expectations and ruling out certain systematics and non-Gaussianity explanations.

Findings

Observed ISW signals are larger than LCDM predictions.

Discrepancy is around 4 sigma for certain aperture sizes.

Primordial non-Gaussianities with F_NL=±100 cannot explain the signal.

Abstract

Through a large ensemble of Gaussian realisations and a suite of large-volume N-body simulations, we show that in a standard LCDM scenario, supervoids and superclusters in the redshift range $z\in[0.4,0.7]$ should leave a {\em small} signature on the ISW effect of the order $\sim 2 \mu$K. We perform aperture photometry on WMAP data, centred on such superstructures identified from SDSS LRGs, and find amplitudes at the level of 8 -- 11$ \mu$K -- thus confirming the earlier work of Granett et al 2008. If we focus on apertures of the size $\sim3.6\degr$, then our realisations indicate that LCDM is discrepant at the level of $\sim4 \sigma$. If we combine all aperture scales considered, ranging from 1\degr--20\degr, then the discrepancy becomes $\sim2\sigma$, and it further lowers to $\sim 0.6 \sigma$ if only 30 superstructures are considered in the analysis (being compatible with no ISW signatures at $1.3\sigma$ 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 CMB maps, and seems to be spatially associated to 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 $\FNL=\pm100$, whilst there is a change in the pattern of temperature anisotropies, all amplitude shifts are well below $<1\mu$K.