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

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 ΛCDM theory prediction exist. We propose a novel method of ISW measurement by cross-correlating cosmic microwave background (CMB) and the LSS traced by 'low-density position' (LDP). 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 ≤ 0.6 over ~20 000 deg² sky coverage. We then cross-correlate with the Planck temperature map and detect the ISW effect at 3.2σ. We further compare the measurement with numerical simulations of the concordance ΛCDM cosmology and find the ISW amplitude parameter A_ISW = 1.14 ± 0.38 when we adopt an LDP definition radius $R_\mathrm{ s}=3^{^{\prime }}$, fully consistent with the prediction of the standard ΛCDM cosmology (A_ISW = 1). This agreement with ΛCDM 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.