The biasing of baryons on the cluster mass function and cosmological parameter estimation

TL;DR

This study investigates how baryonic physics, especially AGN feedback, influences the galaxy cluster mass function and the resulting biases in cosmological parameter estimation, highlighting the importance of accurate modeling for future surveys.

Contribution

It provides a detailed analysis of baryonic effects on the halo mass function using high-resolution simulations and introduces an analytical model to assess these impacts on cosmological measurements.

Findings

AGN feedback reduces baryonic bias in the mass function

Baryonic effects can bias cosmological parameters like σ8 and Ωm

Current surveys are less affected, but future surveys will be significantly biased

Abstract

We study the effect of baryonic processes on the halo mass function in the galaxy cluster mass range using a catalogue of 153 high resolution cosmological hydrodynamical simulations performed with the AMR code ramses. We use the results of our simulations within a simple analytical model to gauge the effects of baryon physics on the halo mass function. Neglect of AGN feedback leads to a significant boost in the cluster mass function similar to that reported by other authors. However, including AGN feedback not only gives rise to systems that are similar to observed galaxy clusters, but they also reverse the global baryonic effects on the clusters. The resulting mass function is closer to the unmodified dark matter halo mass function but still contains a mass dependent bias at the 5-10% level. These effects bias measurements of the cosmological parameters, such as $\sigma_8$ and $\Omega_m$. For current cluster surveys baryonic effects are within the noise for current survey volumes, but forthcoming and planned large SZ, X-ray and multi-wavelength surveys will be biased at the percent level by these processes. The predictions for the halo mass function including baryonic effects need to be carefully studied with larger and improved simulations. However, simulations of full cosmological boxes with the resolution we achieve and including AGN feedback are still computationally challenging.