Measuring the integrated Sachs-Wolfe effect from the low-density regions of the universe

TL;DR

This paper introduces a new method using low-density regions to measure the ISW effect, achieving a detection consistent with ΛCDM predictions and offering an independent approach to address existing tensions in cosmology.

Contribution

The paper presents a novel LDP-based cross-correlation method for ISW detection, reducing selection biases and providing results consistent with standard cosmology.

Findings

Detected ISW effect at 3.2σ significance

Measured ISW amplitude parameter A_ISW=1.14±0.38

Results are consistent with ΛCDM predictions

Abstract

The integrated Sachs-Wolfe (ISW) effect is caused by the decay of cosmological gravitational potential, and is therefore a unique probe of dark energy. However, its robust detection is still problematic. Various tensions between different data sets, different large scale structure (LSS) tracers, and between data and the $\Lambda$CDM theory prediction, exist. We propose a novel method of ISW measurement by cross correlating CMB and the LSS traced by "low-density-position" (LDP, \citet{2019ApJ...874....7D}). It isolates the ISW effect generated by low-density regions of the universe, but insensitive to selection effects associated with voids. We apply it to the DR8 galaxy catalogue of the DESI Legacy imaging surveys, and obtain the LDPs at $z\leq 0.6$ over $\sim$ 20000 $deg^2$ sky coverage. We then cross correlate with the Planck temperature map, and detect the ISW effect at $3.2\sigma$. We further compare the measurement with numerical simulations of the concordance $\Lambda$CDM cosmology, and find the ISW amplitude parameter $A_{ISW}=1.14\pm0.38$ when we adopt a LDP definition radius $R_s=3^{'}$, fully consistent with the prediction of the standard $\Lambda$CDM cosmology ($A_{ISW}=1$). This agreement with $\Lambda$CDM cosmology holds for all the galaxy samples and $R_s$ that we have investigated. Furthermore, the S/N is comparable to that of galaxy ISW measurement. These results demonstrate the LDP method as a competitive alternative to existing ISW measurement methods, and provide independent checks to existing tensions.