Small temperature anisotropies in the Cosmic Microwave Background can be sourced by density perturbations via the late-time integrated Sachs-Wolfe effect. Large voids and superclusters are excellent environments to make a localized measurement of this tiny imprint. In some cases excess signals have been reported. We probed these claims with an independent data set, using the first year data of the Dark Energy Survey in a different footprint, and using a different super-structure finding strategy. We identified 52 large voids and 102 superclusters at redshifts 0.2 < z < 0.65. We used the Jubilee simulation to a priori evaluate the optimal ISW measurement configuration for our compensated top-hat filtering technique, and then performed a stacking measurement of the CMB temperature field based on the DES data. For optimal configurations, we detected a cumulative cold imprint of voids with ∆T f ≈ −5.0 ± 3.7 µK and a hot imprint of superclusters ∆T f ≈ 5.1 ± 3.2 µK ; this is ∼ 1.2σ higher than the expected |∆T f | ≈ 0.6 µK imprint of such super-structures in ΛCDM. If we instead use an a posteriori selected filter size (R/R v = 0.6), we can find a temperature decrement as large as ∆T f ≈ −9.8 ± 4.7 µK for voids, which is ∼ 2σ above ΛCDM expectations and is comparable to previous measurements made using SDSS super-structure data.

Cosmological studies of large scale structure have relied on 2-point statistics, not fully exploiting the rich structure of the cosmic web. In this paper we show how to capture some of this information by using the Minimum Spanning Tree (MST), for the first time using it to estimate cosmological parameters in simulations. Discrete tracers of dark matter such as galaxies, N-body particles or haloes are used as nodes to construct a unique graph, the MST, which is defined to be the minimum weighted spanning graph. We study the dependence of the MST statistics on cosmological parameters using haloes from a suite of COLA simulations with a box size of 250 h −1 Mpc that vary the amplitude of scalar fluctuations (A s ), matter density (Ω m ) and neutrino mass ( m ν ). The power spectrum P(k) and bispectrum B(k 1 , k 2 , k 3 ) are measured between k ∼ 0.125 and 0.5 hMpc −1 , while a corresponding lower cut of ∼ 12.6 h −1 Mpc is applied to the MST. The constraints from the individual methods are fairly similar but when combined we see improved 1σ constraints on Ω m of ∼ 17% with respect to P(k) and ∼ 12% with respect to P(k)+ B(k 1 , k 2 , k 3 ) thus showing the MST is providing additional information not present in the power spectrum and bispectrum. The MST is a tool which can be used to constrain parameters and/or to test systematics in current and future galaxy surveys. This is especially applicable to spectroscopy surveys (BOSS, DESI, Euclid, PSF, WFIRST and 4MOST) where the MST can be applied in 3D comoving coordinates and photometric surveys (DES and LSST) in tomographic shells. The Python code, MiSTree, used to construct the MST and run the analysis, is made publicly available at https://knaidoo29.github.io/mistreedoc/.

Understanding the observed Cold Spot (CS) (temperature of ∼ −150µK at its centre) on the Cosmic Microwave Background (CMB) is an outstanding problem. Explanations vary from assuming it is just a 3σ primordial Gaussian fluctuation to the imprint of a supervoid via the Integrated Sachs-Wolfe and Rees-Sciama (ISW+RS) effects. Since single spherical supervoids cannot account for the full profile, the ISW+RS of multiple line-of-sight voids is studied here to mimic the structure of the cosmic web. Two structure configurations are considered. The first, through simulations of 20 voids, produces a central mean temperature of ∼ −50µK. In this model the central CS temperature lies at ∼ 2σ but fails to explain the CS hot ring. An alternative multi-void model (using more pronounced compensated voids) produces much smaller temperature profiles, but contains a prominent hot ring. Arrangements containing closely placed voids at low redshift are found to be particularly well suited to produce CS-like profiles. We then measure the significance of the CS if CS-like profiles (which are fitted to the ISW+RS of multi-void scenarios) are removed. The CS tension with the ΛCDM model can be reduced dramatically for an array of temperature profiles smaller than the CS itself.

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