Clusters of galaxies: a fundamental pillar of cosmology

Abstract

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 Ωm of the universe. Another interesting component is relativistic particles whose radio emission provide the measure of the magnetic fields (≈μG) in the intra-cluster medium (ICM). The observation of distant clusters of galaxies is also important for cosmology. In particular the new X-ray satellites CHANDRA and XMM yield exciting new results for galaxy cluster physics and cosmology.