Search

Galaxy cluster number counts are an important probe to constrain cosmological parameters. One of the main ingredients of the analysis is the selection function, and in particular the completeness, associated to the cluster sample one is considering. Incorrectly characterising this function can lead to biases in the cosmological constraints. In this work we study the selection function of the Planck cosmological cluster catalogue. In particular, we detail the case in which the cluster model assumed in the detection method differs from the true galaxy clusters, both in terms of profile and shape. We find that varying the cluster pressure profile has a significant effect on the completeness, with clusters with steeper profiles producing a higher completeness than ones with flatter profiles. On the other hand, cluster shapes seem to have a smaller impact on the completeness.

We provide a new scaling relation using a sample of clusters from a full re-observation by the X-ray Chandra telescope of the Planck ESZ catalogue, and compare it to the results of the Planck collaboration obtained from a smaller sample of XMM-Newton observations. We discuss the expected effects of the change of the scaling relation parameters on the cosmological constraints obtained from the Planck cluster sample, and the remaining steps to obtain final constraints from this new scaling relation.

The gas mass fraction in galaxy clusters is a quantity which can be used as a robust cosmological probe. 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 these proceedings we focus on the impact of the hydrostatic equilibrium assumption. From X-ray measurements of cluster gas fraction in the Planck-ESZ sample, we analyse the hydrostatic mass bias B, constraining a possible mass and redshift evolution of this quantity and its impact on the cosmological constraints. We show a degeneracy between the redshift dependence of the bias and cosmological parameters. In particular we find a 3.8σ evidence for a redshift dependence of the bias when assuming a Planck prior on Ωm. On the other hand, assuming a constant mass bias would lead to the extreme large value of Ωm > 0.860. We however show these results to be depending on the mass and redshift selections inside the main sample. Nevertheless, in all the analyses we find a value for the amplitude of the bias that is consistent with B ∼ 0.8, as expected from hydrodynamical simulations and local measurements, but still in tension with the low value of B ∼ 0.6 derived from the combination of cosmic microwave background primary anisotropies with cluster number counts. We also discuss cosmological constraints obtained from gas fraction data, combined with other probes like cluster number counts.

We show the results for the first combined analysis of clusters detected by the Planck satellite and the South Pole Telescope. The combination of these two experiments, with different resolution, mass and redshift range, allows to track the full cosmological evolution of galaxy clusters and the interplay between astrophysics and cosmology. In particular, we exploit the cosmological constraining power of SPT-SZ clusters to provide an independent calibration of Planck scaling relations, and therefore a new estimation of Planck cluster masses. Combining the two cluster catalogs we are thus able to test the hypotheses of self-similarity and hydrostatic equilibrium. We show therefore the huge potentiality of combining catalogs from different experiments, in improving the cosmological analysis and the treatment of different astrophysical and systematic uncertainties.