# Simulating galaxy formation in f(R) modified gravity: Matter, halo, and galaxy-statistics

## TL;DR

This paper investigates the effects of $f(R)$-gravity on galaxy formation and clustering using hydrodynamical simulations, revealing complex interactions between baryonic feedback and modified gravity that influence matter and galaxy statistics.

## Contribution

It provides a comprehensive analysis of matter, halo, and galaxy clustering in $f(R)$-gravity, highlighting the challenges in modeling baryonic effects and the independence of certain halo properties from gravity modifications.

## Key findings

- Matter power spectrum enhancement is difficult to model with baryonic effects.
- Halo mass function changes can be estimated independently from gravity and feedback effects.
- $f(R)$-gravity slightly increases low-mass galaxy populations, reducing galaxy clustering.

## Abstract

We present an analysis of the matter, halo and galaxy clustering in $f(R)$-gravity employing the SHYBONE full-physics hydrodynamical simulation suite. Our analysis focuses on the interplay between baryonic feedback and $f(R)$-gravity in the matter power spectrum, the matter and halo correlation functions, the halo and galaxy-host-halo mass function, the subhalo and satellite-galaxy count and the correlation function of the stars in our simulations. Our studies of the matter power spectrum in full physics simulations in $f(R)$-gravity show, that it will be very difficult to derive accurate fitting formulae for the power spectrum enhancement in $f(R)$-gravity which include baryonic effects. We find that the enhancement of the halo mass function due to $f(R)$-gravity and its suppression due to feedback effects do not show significant back-reaction effects and can thus be estimated from independent GR-hydro and $f(R)$ dark matter only simulations. Our simulations furthermore show, that the number of subhalos and satellite-galaxies per halo is not significantly affected by $f(R)$-gravity. Low mass halos are nevertheless more likely to be populated by galaxies in $f(R)$-gravity. This suppresses the clustering of stars and the galaxy correlation function in the theory compared to standard cosmology.