Non-linear Evolution of f(R) Cosmologies III: Halo Statistics

TL;DR

This paper investigates how f(R) modified gravity theories influence dark matter halo properties, revealing that in certain regimes, gravity modifications significantly alter halo abundance and bias, with implications for testing cosmic acceleration models.

Contribution

It provides a detailed analysis of halo statistics in f(R) cosmologies, demonstrating the applicability of scaling relations and establishing bounds on gravity modifications based on simulation results.

Findings

Enhanced gravity increases massive halo abundance.

Bias of massive halos decreases with modified gravity.

Scaling relations remain useful for setting conservative limits.

Abstract

The statistical properties of dark matter halos, the building blocks of cosmological observables associated with structure in the universe, offer many opportunities to test models for cosmic acceleration, especially those that seek to modify gravitational forces. We study the abundance, bias and profiles of halos in cosmological simulations for one such model: the modified action f(R) theory. In the large field regime that is accessible to current observations, enhanced gravitational forces raise the abundance of rare massive halos and decrease their bias but leave their (lensing) mass profiles largely unchanged. This regime is well described by scaling relations based on a modification of spherical collapse calculations. In the small field regime, enhanced forces are suppressed inside halos and the effects on halo properties are substantially reduced for the most massive halos. Nonetheless, the scaling relations still retain limited applicability for the purpose of establishing conservative upper limits on the modification to gravity.