Constraints on the Early and Late Integrated Sachs-Wolfe effects from Planck 2015 Cosmic Microwave Background Anisotropies angular power spectra

TL;DR

This paper uses Planck 2015 CMB data to measure and constrain the early and late Integrated Sachs-Wolfe effects, providing significant detection of the early ISW and evidence for the late ISW, consistent with standard cosmology.

Contribution

It provides the first precise constraints on early and late ISW effects using Planck 2015 data, including polarization, and discusses their stability under additional cosmological parameters.

Findings

Early ISW detected at high significance with A_eISW ≈ 1.06

Late ISW constrained with an upper limit of A_lISW < 1.1

Results are consistent with standard cosmological model

Abstract

The Integrated Sachs-Wolfe (ISW) effect predicts additional anisotropies in the Cosmic Microwave Background due to time variation of the gravitational potential when the expansion of the universe is not matter dominated. The ISW effect is therefore expected in the early universe, due to the presence of relativistic particles at recombination, and in the late universe, when dark energy starts to dominate the expansion. Deviations from the standard picture can be parameterized by $A_{e\text{ISW}}$ and $A_{l\text{ISW}}$, which rescale the overall amplitude of the early and late ISW effects. Analyzing the most recent CMB temperature spectra from the Planck 2015 release, we detect the presence of the early ISW at high significance with $A_{e\mathrm{ISW}} = 1.06\pm0.04$ at 68% CL and an upper limit for the late ISW of $A_{l\mathrm{ISW}} < 1.1$ at 95% CL. The inclusion of the recent polarization data from the Planck experiment results in $A_{e\mathrm{ISW}} = 0.999\pm0.028$ at 68% CL, in better agreement with the value $A_{e\mathrm{ISW}} = 1$ of a standard cosmology. When considering the recent detections of the late ISW coming from correlations between CMB temperature anisotropies and weak lensing, a value of $A_{l\mathrm{ISW}}=0.85\pm0.21$ is predicted at 68% CL, showing a $4\sigma$ evidence. We discuss the stability of our result in the case of an extra relativistic energy component parametrized by the effective neutrino number $N_\mathrm{eff}$ and of a CMB lensing amplitude $A_\mathrm{L}$.