Prospects for measuring the relative velocities of galaxy clusters in photometric surveys using the kinetic Sunyaev-Zel'dovich Effect

TL;DR

This paper explores the potential of using photometric surveys combined with mm-wave data to measure galaxy cluster velocities via the kinetic Sunyaev-Zel'dovich effect, enabling tests of gravity and structure formation.

Contribution

It demonstrates that current and next-generation surveys can detect the pairwise kSZ signal with high significance, even accounting for redshift errors, and discusses implications for gravity theories.

Findings

DES + SPT can detect the kSZ signal at 8-13 sigma.

Spectroscopic redshifts could improve detection to 26-43 sigma.

High-precision measurements can inform models of gravity and cluster gas content.

Abstract

We consider the prospects for measuring the pairwise kinetic Sunyaev-Zel'dovich (kSZ) signal from galaxy clusters discovered in large photometric surveys such as the Dark Energy Survey (DES). We project that the DES cluster sample will, in conjunction with existing mm-wave data from the South Pole Telescope (SPT), yield a detection of the pairwise kSZ signal at the 8-13 sigma level, with sensitivity peaking for clusters separated by ~100 Mpc distances. A next-generation version of SPT would allow for a 18-30 sigma detection and would be limited by variance from the kSZ signal itself and residual thermal Sunyaev-Zel'dovich (tSZ) signal. Throughout our analysis we assume photometric redshift errors, which wash out the signal for clusters separated by <~50 Mpc; a spectroscopic survey of the DES sample would recover this signal and allow for a 26-43 sigma detection, and would again be limited by kSZ/tSZ variance. Assuming a standard model of structure formation, these high-precision measurements of the pairwise kSZ signal will yield detailed information on the gas content of the galaxy clusters. Alternatively, if the gas can be sufficiently characterized by other means (e.g. using tSZ, X-ray, or weak lensing), then the relative velocities of the galaxy clusters can be isolated, thereby providing a precision measurement of gravity on 100 Mpc scales. We briefly consider the utility of these measurements for constraining theories of modified gravity.