Cosmology with Clusters of Galaxies

Abstract

Clusters constitute one major source of informations for cosmology. In the present paper, I concentrate on the vision on X-ray clusters from a theorist point of view and more specifically on the way they can be used for the determination of the matter density parameter of the universe Ω_m. I describe the usual modeling of X-ray clusters for cosmological applications and the scaling relations that are used in this modeling. I then discuss several cosmological tests based on clusters properties. The first method uses the evolution of the abundance of clusters with redshift, the second one make use of the baryon fraction in clusters. The former method needs reliable estimates of the local temperature distribution function as well as at high redshift. The latter can provide a direct estimate of Ω₀ provide that we have a reliable estimate of the baryon content of clusters and a good estimate of the primordial baryonic abundance Ω_b. Finally, I will illustrate an iconoclast point of view accordingly to which no definitive conclusions have been achieved by these methods. Although low density universes are favored by most authors, I argue that present day observations can also be interpreted as providing evidence for a high density universe.