Constraining cosmological parameters using the pairwise kinematic Sunyaev-Zel'dovich effect with CMB-S4 and future galaxy cluster surveys

TL;DR

This paper forecasts how future CMB-S4 and galaxy surveys can precisely measure the pairwise kSZ effect to constrain cosmological parameters, including dark energy and gravity theories, with high significance.

Contribution

It provides the first detailed forecast of the pairwise kSZ measurement capabilities of CMB-S4, including systematic uncertainties and their impact on cosmological constraints.

Findings

CMB-S4 can reject zero pairwise kSZ signal at 36σ.

Systematic effects can reduce the signal-to-noise ratio by 20%.

Constraints on the growth index γ will reach 28σ, strongly testing gravity theories.

Abstract

We present a forecast of the pairwise kinematic Sunyaev-Zel'dovich (kSZ) measurement that will be achievable with the future CMB-S4 experiment. CMB-S4 is the next stage for ground-based cosmic microwave background experiments, with a planned wide area survey that will observe approximately $50\%$ of the sky. We construct a simulated sample of galaxy clusters that have been optically selected in an LSST-like survey and have spectroscopic redshifts. For this cluster sample, we predict that CMB-S4 will reject the null hypothesis of zero pairwise kSZ signal at $36 \,\sigma$. We estimate the effects of systematic uncertainties such as scatter in the mass-richness scaling relation and cluster mis-centering. We find that these effects can reduce the signal-to-noise ratio of the CMB-S4 pairwise kSZ measurement by $20\%$. We explore the constraining power of the measured kSZ signal in combination with measurements of the galaxy clusters' thermal SZ emission on two extensions to the standard cosmological model. The first extension allows the dark energy equation of state $w$ to vary. We find the CMB-S4 pairwise kSZ measurement yields a modest reduction in the uncertainty on $w$ by a factor of 1.36 over the \Planck's 2018 uncertainty. The second extension tests General Relativity by varying the growth index $\gamma$. We find that CMB-S4's pairwise kSZ measurement will yield a $28\sigma$ constraint on $\gamma$, and strongly constrain alternative theories of gravity.