The Lyman-alpha forest in f(R) modified gravity

TL;DR

This study uses hydrodynamical simulations to assess the impact of f(R) gravity on the Lyman-alpha forest, finding minimal effects that limit current observational constraints.

Contribution

First detailed hydrodynamical simulation analysis of f(R) gravity effects on Lyman-alpha forest statistics, showing limited impact on observable properties.

Findings

f(R) gravity has less than 10% effect on Lyman-alpha flux PDFs and power spectra

Column density and line width distributions are largely unaffected by f(R) modifications

Current data cannot constrain f(R) models due to small impact and observational systematics

Abstract

In this work, we analyze the Lyman-$\alpha$ forest in cosmological hydrodynamical simulations of chameleon-type f(R) gravity with the goal to assess whether the impact of such models is detectable in absorption line statistics. We carry out a set of hydrodynamical simulations with the cosmological simulation code MG-GADGET, including star formation and cooling effects, and create synthetic Lyman-$\alpha$ absorption spectra from the simulation outputs. We statistically compare simulations with f(R) and ordinary general relativity, focusing on flux probability distribution functions (PDFs) and flux power-spectra, an analysis of the column density and line width distributions, as well as the matter power spectrum. We find that the influence of f(R) gravity on the Lyman-$\alpha$ forest is rather small. Even models with strong modifications of gravity, like $|\bar{f}_{R0}| = 10^{-4}$, do not change the statistical Lyman-$\alpha$ properties by more than 10%. The column density and line width distributions are hardly affected at all. It is therefore not possible to get competitive constraints on the background field $f_R$ using current observational data. An improved understanding of systematics in the observations and a more accurate modeling of the baryonic/radiative physics would be required to allow this in the future. The impact of f(R) on the matter power spectrum in our results is consistent with previous works.