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

We infer the mean optical depth of a sample of optically selected galaxy clusters from the Dark Energy Survey via the pairwise kinematic Sunyaev-Zel'dovich (KSZ) effect. The pairwise KSZ signal between pairs of clusters drawn from the Dark Energy Survey Year-3 cluster catalog is detected at 4.1 sigma in cosmic microwave background 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 similar to 1; 400 deg2 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 tau over bar e = (2.97 +/- 0.73) x 10-3, while that inferred from the thermal SZ signal is tau over bar e = (2.51 +/- 0.55stat +/- 0.15syst) x 10-3. The two measures agree at 0.6 sigma. We perform a suite of systematic checks to test the robustness of the analysis.

Automated summary

We use the pairwise kinematic Sunyaev-Zel'dovich (KSZ) effect to infer the average optical depth of a sample of optically selected galaxy clusters from the Dark Energy Survey. The pairwise KSZ signal is detected at 4.1 sigma in cosmic microwave background temperature maps from two years of observations with the SPT-3G camera. After data cuts, there are 24,580 clusters in the observed area. We calculate the mean optical depth using two techniques: the pairwise KSZ signal gives tau over bar e = (2.97 +/- 0.73) x 10-3, while the thermal SZ signal gives tau over bar e = (2.51 +/- 0.55stat +/- 0.15syst) x 10-3. The two measures agree within 0.6 sigma. We perform systematic checks to ensure the validity of our analysis.