Constraining the mass and redshift evolution of the hydrostatic mass bias using the gas mass fraction in galaxy clusters

TL;DR

This study investigates how the hydrostatic mass bias in galaxy clusters varies with mass and redshift, affecting cosmological parameter estimates, and finds evidence for redshift dependence with implications for cosmological constraints.

Contribution

It constrains the mass and redshift evolution of hydrostatic mass bias using gas mass fraction data from galaxy clusters, highlighting its impact on cosmological parameters.

Findings

Evidence for redshift dependence of the hydrostatic bias with 3.8 sigma significance.

Degeneracy between bias evolution and cosmological parameters, especially mbda_m.

Bias amplitude consistent with simulations but in tension with CMB and cluster count results.

Abstract

The gas mass fraction in galaxy clusters is a convenient probe to use in cosmological studies, as it can help derive constraints on a collection of cosmological parameters. It is however subject to various effects from the baryonic physics inside galaxy clusters, which may bias the obtained cosmological constraints. Among different aspects of the baryonic physics, in this paper we focus on the impact of the hydrostatic equilibrium assumption. We analyse the hydrostatic mass bias $B$, constraining a possible mass and redshift evolution of this quantity and its impact on the cosmological constraints. To that end we consider cluster observations of the {\it Planck}-ESZ sample and evaluate the gas mass fraction using X-ray counterpart observations. We show a degeneracy between the redshift dependence of the bias and cosmological parameters. In particular we find a $3.8 \sigma$ evidence for a redshift dependence of the bias when assuming a {\it Planck} prior on $\Omega_m$. On the other hand, assuming a constant mass bias would lead to the extreme large value of $\Omega_m > 0.849$. We however show that our results are entirely dependent on the cluster sample we consider. In particular, the mass and redshift trends that we find for the lowest mass-redshift and highest mass-redshift clusters of our sample are not compatible. Nevertheless, in all the analyses we find a value for the amplitude of the bias that is consistent with $B \sim 0.8$, as expected from hydrodynamical simulations and local measurements, but still in tension with the low value of $B \sim 0.6$ derived from the combination of cosmic microwave background primary anisotropies with cluster number counts.