Orateur
Description
The gas mass fraction in galaxy clusters is a convenient tool to use in the context of cosmological studies.
Indeed this quantity allows to constrain the universal baryon fraction $\Omega_b/\Omega_m$, as well as other parameters like the matter density $\Omega_m$, the Hubble parameter $h$ or the Equation of State of Dark Energy $w$.
This gas mass fraction is also sensitive to baryonic effects that need to be taken into account, and that translate into nuisance parameters.
Two of them are the depletion factor $\Upsilon$ and the hydrostatic mass bias $B = (1 - b)$.
The former describes how baryons are depleted in clusters with respect to the universal baryon fraction, while the latter encodes the bias of the mass derived from X-ray observations under the hypothesis of hydrostatic equilibrium.
We will show preliminary results, based on the {\it Planck}-ESZ clusters observed by XMM-{\it Newton}, on both cosmological and cluster parameters.
We will notably discuss our investigation on a possible redshift and mass dependence of the mass bias, which is considered to be non-existent in hydrodynamic simulations based on $\Lambda$-CDM, and compare our results with other studies.
Finally we show that our results on the mass and redshift evolution of the mass bias exhibit a sample dependent behaviour, especially given particular mass and redshift selections.
An evolution of the bias nevertheless needs to be taken into account to derive robust cosmological constraints as we show a degeneracy between a redshift dependence of the bias and cosmological parameters.
| Field | Cosmology |
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