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 $\Lambda$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.
