A lower density universe? - Measuring imprints of large scale structure on the CMB

Large-scale structures (LSS) can leave various imprints on the cosmic microwave background(CMB). Two main features come from the spatial and temporal perturbations of the CMB photon trajectory due to LSS: weak lensing and the integrated Sachs-Wolfe effect. I will give a summary of our paper "Galaxy clustering in Legacy Survey and its imprint on the CMB" (arXiv: 2010.00466), where we use the DESI Legacy Imaging Survey to extract cosmological information from the above effects in the redshift range 0<z<0.8. The Legacy Survey, covering about a third of the sky area and containing tens of millions of galaxies, is excellent for the purpose of cross-correlation studies, although a difficulty is to obtain a robust redshift distribution for those galaxies given the very limited photometric bands. In this study, we use our own method to find competitive photometric redshifts using colour information and construct galaxy density maps in four tomographic redshift slices. These maps are cross-correlated in angular space with the Planck 2018 lensing convergence and temperature maps. By comparing our measurements with theoretical predictions from the standard Lambda-CDM model assuming Planck 2018 cosmology, we find that interestingly the lensing amplitude is lower than expected, consistent with other weak lensing results. This may add to the existing tension in the Omega_m-sigma_8 parameter space.