A measurement of the mean central optical depth of galaxy clusters via the pairwise kinematic Sunyaev-Zel'dovich effect with SPT-3G and DES

TL;DR

This paper measures the average optical depth of galaxy clusters using the pairwise kSZ effect with data from DES and SPT-3G, achieving a significant detection and consistent results with thermal SZ measurements.

Contribution

It provides the first measurement of the mean optical depth of optically-selected galaxy clusters via the pairwise kSZ effect using DES and SPT-3G data.

Findings

Detected the pairwise kSZ signal at 4.1 sigma significance.

Inferred the mean optical depth as approximately 3 x 10^-3.

Results from kSZ and thermal SZ methods are consistent within uncertainties.

Abstract

We infer the mean optical depth of a sample of optically-selected galaxy clusters from the Dark Energy Survey (DES) via the pairwise kinematic Sunyaev-Zel'dovich (kSZ) effect. The pairwise kSZ signal between pairs of clusters drawn from the DES Year-3 cluster catalog is detected at $4.1 \sigma$ in cosmic microwave background (CMB) temperature maps from two years of observations with the SPT-3G camera on the South Pole Telescope. After cuts, there are 24,580 clusters in the $\sim 1,400$ deg$^2$ of the southern sky observed by both experiments. We infer the mean optical depth of the cluster sample with two techniques. The optical depth inferred from the pairwise kSZ signal is $\bar{\tau}_e = (2.97 \pm 0.73) \times 10^{-3}$, while that inferred from the thermal SZ signal is $\bar{\tau}_e = (2.51 \pm 0.55^{\text{stat}} \pm 0.15^{\rm syst}) \times 10^{-3}$. The two measures agree at $0.6 \sigma$. We perform a suite of systematic checks to test the robustness of the analysis.