An estimate of the local ISW signal, and its impact on CMB anomalies

TL;DR

This paper estimates the local ISW signal from galaxy data up to redshift 0.3 and shows that removing this foreground reduces the significance of certain large-scale anomalies in the WMAP CMB data.

Contribution

It provides a new method to estimate the local ISW effect and demonstrates its impact on observed CMB anomalies, improving understanding of foreground effects.

Findings

Removing the local ISW signal decreases the significance of large-scale CMB anomalies.

The local ISW contribution accounts for part of the observed anomalies.

Foreground subtraction alters interpretations of CMB large-scale features.

Abstract

We estimate the local density field in redshift shells to a maximum redshift of z=0.3, using photometric redshifts for the 2MASS galaxy catalogue, matched to optical data from the SuperCOSMOS galaxy catalogue. This density-field map is used to predict the Integrated Sachs-Wolfe (ISW) CMB anisotropies that originate within the volume at z<0.3. We investigate the impact of this estimated ISW foreground signal on large-scale anomalies in the WMAP CMB data. We find that removal of the foreground ISW signal from WMAP data reduces the significance of a number of reported large-scale anomalies in the CMB, including the low quadrupole power and the apparent alignment between the CMB quadrupole and octopole.