A measurement of the Integrated Sachs-Wolfe Effect with the Rapid ASKAP Continuum Survey

TL;DR

This paper measures the Integrated Sachs-Wolfe effect by cross-correlating Planck CMB maps with RACS radio galaxy data, finding results consistent with the standard cosmological model and detecting a large-scale power excess.

Contribution

It provides the first measurement of the ISW effect using RACS data, confirming the accelerated expansion of the universe and analyzing large-scale galaxy clustering.

Findings

Detected a positive ISW cross-correlation at ~2.8 sigma

Measured the ISW amplitude as A_ISW = 0.94^{+0.42}_{-0.41}

Observed a power excess in galaxy auto-correlation on large scales

Abstract

The evolution of the gravitational potentials on large scales due to the accelerated expansion of the Universe is an important and independent probe of dark energy, known as the integrated Sachs-Wolfe (ISW) effect. We measure this ISW effect through cross-correlating the cosmic microwave background maps from the Planck satellite with a radio continuum galaxy distribution map from the recent Rapid ASKAP Continuum Survey (RACS). We detect a positive cross-correlation at $\sim 2.8\,\sigma$ relative to the null hypothesis of no correlation. We parameterise the strength of the ISW effect through an amplitude parameter and find the constraints to be $A_{\mathrm{ISW}} = 0.94^{+0.42}_{-0.41}$, which is consistent with the prediction of an accelerating universe within the current concordance cosmological model, $\Lambda$CDM. The credible interval on this parameter is independent of the different bias models and redshift distributions that were considered when marginalising over the nuisance parameters. We also detect a power excess in the galaxy auto-correlation angular power spectrum on large scales ($\ell \leq 40$), and investigate possible systematic causes.