# The separate and combined effects of baryon physics and neutrino free-streaming on large-scale structure

## TL;DR

This study investigates how baryon physics, especially AGN feedback, and neutrino free-streaming independently and jointly influence large-scale structure, showing their effects can often be approximated separately with high accuracy.

## Contribution

It provides a detailed analysis of the separate and combined impacts of baryon physics and neutrinos on large-scale structure diagnostics using hydrodynamical simulations, demonstrating their effects can be treated independently in most cases.

## Key findings

- Both AGN feedback and neutrinos suppress the matter power spectrum.
- AGN feedback reduces group and cluster masses, alters density profiles.
- Neutrinos lower cluster masses without significantly changing density profiles.

## Abstract

We use the cosmo-OWLS and BAHAMAS suites of cosmological hydrodynamical simulations to explore the separate and combined effects of baryon physics (particularly feedback from active galactic nuclei, AGN) and free-streaming of massive neutrinos on large-scale structure. We focus on five diagnostics: i) the halo mass function; ii) halo mass density profiles; iii) the halo mass-concentration relation; iv) the clustering of haloes; and v) the clustering of matter; and we explore the extent to which the effects of baryon physics and neutrino free-streaming can be treated independently. Consistent with previous studies, we find that both AGN feedback and neutrino free-streaming suppress the total matter power spectrum, although their scale and redshift dependencies differ significantly. The inclusion of AGN feedback can significantly reduce the masses of groups and clusters, and increase their scale radii. These effects lead to a decrease in the amplitude of the mass-concentration relation and an increase in the halo autocorrelation function at fixed mass. Neutrinos also lower the masses of groups and clusters while having no significant effect on the shape of their density profiles (thus also affecting the mass-concentration relation and halo clustering in a qualitatively similar way to feedback). We show that, with only a small number of exceptions, the combined effects of baryon physics and neutrino free-streaming on all five diagnostics can be estimated to typically better than a few percent accuracy by treating these processes independently (i.e., by multiplying their separate effects).