Mass bias evolution in tSZ cluster cosmology.

Galaxy clusters observed through the thermal Sunyaev-Zeldovich (tSZ) effect are a recent cosmological probe. The precision on the cosmological constraints is mainly affected by the current knowledge of clusters physics, that enters the analysis through the scaling relations. We study one of the most important sources of systematic uncertainties, the mass bias $(1-b)$. We analyse the effects of a mass-redshift dependence, adopting a power-law parametrisation. We apply this parametrisation to the combination of tSZ number counts and power spectrum, finding a hint for redshift dependence that leads to an increasing value of the mass bias for higher redshift. We test the robustness of our results for different weak lensing calibrations and a discrete redshift dependence. We find our results to be dependent on the clusters sample that we are considering, in particular obtaining an inverse (decreasing) redshift dependence when neglecting $z<0.2$ clusters. We analyse the effects of this parametrisation on the combination of cosmic microwave background (CMB) primary anisotropies and tSZ galaxy clusters. We find a preferred constant value of mass bias, $(1-b) =0.62 \pm 0.05$, that is too low with respect to weak lensing and numerical simulations estimations. Therefore we conclude that this mass-redshift parametrisation does not help in solving the remaining discrepancy between CMB and tSZ clusters observations.