Cross-correlation of Planck CMB lensing with DESI galaxy groups

TL;DR

This study measures the cross-correlation between DESI galaxy groups and Planck CMB lensing, confirming large-scale structure signals and revealing bias dependence on group mass, with implications for cosmology and tSZ contamination correction.

Contribution

It provides the first detailed measurement of galaxy group-CMB lensing cross-correlation across various redshifts and masses, and compares observed bias with theoretical predictions.

Findings

High significance detections with S/N up to 50.

Bias measurements agree with theory at high redshift, but are lower at low redshift.

tSZ contamination affects the cross-correlation at about 30%.

Abstract

We measure the cross-correlation between galaxy groups constructed from DESI Legacy Imaging Survey DR8 and \emph{Planck} CMB lensing, over overlapping sky area of 16876 $\rm deg^2$. The detections are significant and consistent with the expected signal of the large-scale structure of the universe, over group samples of various redshift, mass, richness $N_{\rm g}$ and over various scale cuts. The overall S/N is 40 for a conservative sample with $N_{\rm g}\geq 5$, and increases to $50$ for the sample with $N_{\rm g}\geq 2$. Adopting the \emph{Planck} 2018 cosmology, we constrain the density bias of groups with $N_{\rm g}\geq 5$ as $b_{\rm g}=1.31\pm 0.10$, $2.22\pm 0.10$, $3.52\pm 0.20$ at $0.1<z\leq 0.33$, $0.33<z\leq 0.67$, $0.67<z\leq1$ respectively. The group catalog provides the estimation of group halo mass and therefore allows us to detect the dependence of bias on group mass with high significance. It also allows us to compare the measured bias with the theoretically predicted one using the estimated group mass. We find excellent agreement for the two high redshift bins. However, it is lower than the theory by $\sim 3\sigma$ for the lowest redshift bin. Another interesting finding is the significant impact of the thermal Sunyaev Zel'dovich (tSZ). It contaminates the galaxy group-CMB lensing cross-correlation at $\sim 30\%$ level, and must be deprojected first in CMB lensing reconstruction.