Cluster Abundance in f(R) Gravity Models

TL;DR

This paper uses N-body simulations to study how modifications in f(R) gravity models affect galaxy cluster abundance, demonstrating the effectiveness of a spherical collapse model for constraining such theories.

Contribution

It introduces a comprehensive class of f(R) models, compares simulation results with a spherical collapse model, and provides a method to translate cluster abundance constraints across models.

Findings

Spherical collapse model accurately predicts halo abundance in large-field f(R) models.

Simulation results align with the spherical collapse model across various f(R) parameters.

Constraints from local X-ray cluster observations can be mapped onto different f(R) models.

Abstract

As one of the most powerful probes of cosmological structure formation, the abundance of massive galaxy clusters is a sensitive probe of modifications to gravity on cosmological scales. In this paper, we present results from N-body simulations of a general class of f(R) models, which self-consistently solve the non-linear field equation for the enhanced forces. Within this class we vary the amplitude of the field, which controls the range of the enhanced gravitational forces, both at the present epoch and as a function of redshift. Most models in the literature can be mapped onto the parameter space of this class. Focusing on the abundance of massive dark matter halos, we compare the simulation results to a simple spherical collapse model. Current constraints lie in the large-field regime, where the chameleon mechanism is not important. In this regime, the spherical collapse model works equally well for a wide range of models and can serve as a model-independent tool for placing constraints on f(R) gravity from cluster abundance. Using these results, we show how constraints from the observed local abundance of X-ray clusters on a specific f(R) model can be mapped onto other members of this general class of models.