Planck 2015 results. XXI. The integrated Sachs-Wolfe effect

TL;DR

This paper analyzes the ISW effect using Planck 2015 data, detecting it at 4 sigma through cross-correlations with large-scale structure tracers and improving the reconstruction of ISW temperature fluctuations.

Contribution

It provides the first detection of the ISW effect from Planck data through multiple cross-correlations and enhances the reconstruction of ISW anisotropies using combined LSS tracers.

Findings

ISW effect detected at 4 sigma significance

Planck data alone detects ISW at approximately 3 sigma

Reconstructed ISW map with improved accuracy and uncertainty estimates

Abstract

This paper presents a study of the ISW effect from the Planck 2015 temperature and polarization data release. The CMB is cross-correlated with different LSS tracers: the NVSS, SDSS and WISE catalogues, and the Planck 2015 lensing map. This cross-correlation yields a detection at $4\,\sigma$, where most of the signal-to-noise is due to the Planck lensing and NVSS. In fact, the ISW effect is detected only from the Planck data (through the ISW-lensing bispectrum) at $\approx 3\,\sigma$, which is similar to the detection level achieved by combining the cross-correlation signal coming from all the catalogues. The ISW signal allow us to detect $\Omega_\Lambda$ at more than $3\,\sigma$. This cross-correlation analysis is performed only with the Planck temperature data, since the polarization scales available in the 2015 release do not permit significant improvement of the CMB-LSS cross-correlation detectability. Nevertheless, polarization data is used to study the anomalously large ISW signal previously reported through the stacking of CMB features at the locations of known superstructures. We find that the current Planck polarization data do not exclude that this signal could be caused by the ISW effect. In addition, the stacking of the Planck lensing map on the locations of superstructures exhibits a positive cross-correlation with these large-scale structures. Finally, we have improved our previous reconstruction of the ISW temperature fluctuations by combining the information encoded in all the previously mentioned LSS tracers. In particular, we construct a map of the ISW secondary anisotropies and the corresponding uncertainties map, obtained from simulations. We also explore the reconstruction of the ISW anisotropies caused by the LSS traced by the 2MPZ survey by directly inverting the density field into the gravitational potential field.