B16 - Non-linear structure growth traced by galaxy clusters

Principal Investigators: M. Bartelmann (Heidelberg); T. Erben (Bonn)


The galaxy-cluster population is among the most sensitive probes for the nature of Dark Energy, if not the most sensitive. This is because clusters populate the most massive end of the mass function of cosmic objects, the amplitude of which depends exponentially on the growth factor of cosmic structures. Galaxy clusters offer numerous observables: strong and weak gravitational lensing are directly determined by the second derivatives of the line-of-sight projected gravitational potential, X-ray emission and the Sunyaev-Zel'dovich effect of the thermal intracluster plasma are characterised by the gravitational potential itself if hydrostatic equilibrium prevails, and the overdensity of galaxies, red galaxies in particular, marks clusters in the optical and infrared bands. Biases plaguing cluster samples defined by one observable can be reduced or avoided if as many observables as possible are combined to construct cluster catalogues. Based on multi-band linear filtering techniques developed in the past years, we propose to construct the perhaps most cleanly defined cluster samples from available survey data, and to interpret our findings cosmologically. In particular, we shall apply a linear filter jointly searching for cluster peaks in galaxy counts, in redshift space, in the weak-lensing signal, in X-ray counts and in the thermal Sunyaev-Zel’dovich signal, where available. Particular emphasis will be placed on a robust estimate of the signal-to-noise ratio. Regarding the cosmological interpretation of the results, our main goal will be to test the null hypothesis that the cluster counts can be explained by the standard, ΛCDM cosmology with a cosmological constant.

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