Galaxy Cluster Statistics in Modified Gravity Cosmologies

TL;DR

This paper explores how galaxy cluster statistics can reveal deviations from general relativity in modified gravity models, analyzing simulations to identify observable differences in cluster properties across redshifts.

Contribution

It provides a comparative analysis of galaxy cluster statistics in DGP and f(R) gravity models using N-body simulations, highlighting potential observational signatures.

Findings

Systematic differences in cluster mass function, power spectrum, and velocities between gravity models.

Mean pairwise velocity as a key consistency test for modified gravity.

Upcoming experiments could detect these differences via cluster observations.

Abstract

If the accelerated expansion of the universe is due to a modification of general relativity at late times, it is likely that the growth of structure on large scales would also display deviations from the standard cosmology. We investigate the statistics of the distribution of galaxy cluster-sized halos as a probe of gravity. We analyze the output of several matched N-body simulations with the same initial conditions and expansion histories but using both DGP and f (R) gravity with various parameters. From each simulation we extract the cluster mass function, power spectrum, and mean pairwise velocity at redshifts 1, 0.3, and 0. All three statistics display systematic differences between gravity theories. The mean pairwise velocity provides an important consistency test for any posited departure from general relativity suggested by measurements of the power spectrum and cluster mass function. Upcoming microwave background experiments, including Simons Observatory and CMB- S4, will detect tens of thousands of galaxy clusters via the thermal Sunyaev-Zeldovich effect, probe their masses with lensing of the microwave background, and potentially measure velocities using the transverse lensing effect or the kinematic Sunyaev-Zeldovich effect. These cluster measurements promise to be a substantial probe of modified gravity.