Implication of an evolution of the mean pressure profile of galaxy clusters on the cosmological parameters estimated from the Planck tSZ power spectrum
Most recent studies show that the tension observed between the cosmological constraints based on cluster abundance from SZ catalogs and from CMB primary anisotropies can be cancelled by a variation of the hydrostatic bias parameter. However, the value of the hydrostatic bias needed in order to alleviate this tension is in strong disagreement with the current estimates of this parameter based on lensing, X-ray, and SZ observations.
The mean pressure profile of the galaxy cluster population plays an essential role in cosmological analyses. It is used in cluster counts analyses in order to estimate the value of the integrated Compton parameter of each cluster in tSZ catalogs and in analyses based on the tSZ power spectrum in order to model the latter. While the modification of the shape of the mean pressure profile only has an effect at high multipole, a variation of its amplitude plays a role that is similar to the one of the hydrostatic bias in cosmological analyses. If the self-similar hypothesis is not verified in the whole mass-redshift plane, the amplitude of the mean pressure profile of the cluster population could be different from the one observed at high mass and low redshift.
I will present an analysis of the Planck tSZ power spectrum based on threes different mean pressure profiles. This study shows that a variation of the amplitude of the mean pressure profile of the cluster population, compatible with the current constraints on the cluster gas mass fraction, leads to significant differences in the final cosmological parameter estimates. I will conclude on the necessity to accurately characterize the shape, the intrinsic scatter and the redshift evolution of the mean pressure profile in order to estimate part of the biases and systematic effects that currently prevent cosmological analyses based on tSZ surveys to obtain precise and unbiased cosmological constraints. This is one of the goals of the on-going NIKA2 SZ large program.