## The biasing of baryons on the cluster mass function and cosmological parameter estimation    [PDF]

Davide Martizzi, Irshad Mohammed, Romain Teyssier, Ben Moore
The dark matter halo mass function is an extremely important quantity that will be measured to high precision by ongoing and next generation surveys. It is therefore crucial to determine which are the theoretical uncertainties that need to be taken into account when comparing the observed halo mass function to the predictions of theoretical cosmological models and numerical simulations. In this paper 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. We find that 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. We then explore how 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 surveys will be highly biased by these processes.
View original: http://arxiv.org/abs/1307.6002