COSMOLOGY WITH CLUSTERS OF GALAXIES

In this Chapter I review the role that galaxy clusters play as tools to constrain cosmological parameters. I will concentrate mostly on the application of the mass function of galaxy clusters, while other methods, such as that based on the baryon fraction, are covered by other Chapters of the book. Since most of the cosmological applications of galaxy clusters rely on precise measurements of their masses, a substantial part of my Lectures concentrates on the different methods...

I critically review a methodology of using clusters of galaxies as cosmological probes. The understanding of the abundances and spatial correlations of dark matter halos has been significantly advanced especially for a last few years. Nevertheless such dark matter halos are not necessarily identical to clusters of galaxies in the universe. This is a quite obvious fact, but it seems that the resulting systematic errors, on the cosmological parameter estimates for instance, are...

Surveys of galaxy clusters provide a promising method of testing models of structure formation in the universe. Within the context of our standard structure formation scenario, surveys provide measurements of the geometry of the universe and the nature of the dark energy and dark matter. Cluster catalogues will be constructed using some combination of X-ray, optical/near--IR, and mm or cm-wave observations. These catalogues will be used to study the cluster redshift and mass ...

Clusters of galaxies are used in a variety of ways to do cosmology. Some of them are presented here. Their X-ray emitting gas allows us to determine the baryon fraction, dark matter distribution and the matter density $\Omega_{m}$ of the universe. Another interesting component is relativistic particles whose radio emission provide the measure of the magnetic fields ($\approx \mu G$) in the intra-cluster medium (ICM). The observation of distant clusters of galaxies is also imp...

A few, simple and qualitative examples of the potential of galaxy clusters as diagnostics of cosmology are presented. In relation to these we discuss briefly three ongoing or forthcoming cluster surveys in the optical/NIR, X-rays and the cosmic microwave radiation background.

Clusters of galaxies are self-gravitating systems of mass ~10^14-10^15 Msun. They consist of dark matter (~80 %), hot diffuse intracluster plasma (< 20 %) and a small fraction of stars, dust, and cold gas, mostly locked in galaxies. In most clusters, scaling relations between their properties testify that the cluster components are in approximate dynamical equilibrium within the cluster gravitational potential well. However, spatially inhomogeneous thermal and non-thermal emi...

The determination of galaxy cluster mass is of great importance since it is directly linked to the well- known problem of dark matter in the Universe and to the cluster baryon content. X-ray observations from satellites have enabled a better understanding of the physics occuring inside clusters, their matter content as well as a detailed description of their structure. In addition, the discovery of giant gravitational arcs and the lensing properties of clusters of galaxies re...

In recent years, significant progress has been made in building new galaxy clusters samples, at low and high redshifts, from wide-area surveys, particularly exploiting the Sunyaev--Zel'dovich (SZ) effect. A large effort is underway to identify and characterize these new systems with optical/NIR and X-ray facilities, thus opening new avenues to constraint cosmological models using structure growth and geometrical tests. A census of galaxy clusters sets constraints on reionizat...

The links between the internal structure of galaxy groups and clusters and cosmological parameters are reviewed here. The mass density profiles of clusters, inferred from both optical analyses of the galaxy surface number density profile coupled with internal kinematics, and from weak gravitational lensing, appear cuspy with inner density profiles at least as steep as $r^{-1}$, as is expected from high-resolution cosmological $N$-body simulations starting with scale-free or C...

What is the role of clusters of galaxies in probing the large-scale velocity field of the universe? We investigate the distribution of peculiar velocities of clusters of galaxies in the popular low-density ($\Omega=0.3$) flat Cold-Dark-Matter (CDM) cosmological model, which best fits many large-scale structure observations. An $\Omega=1$ CDM model is also studied for comparison. We find that clusters of galaxies are efficient tracers of the large-scale velocity field. The clu...