# Les amas de galaxies: des outiles pour etudier la formation des structures et la cosmologie

Abstract : Clusters of galaxies are the largest gravitational bound objects in our universe. In the scenario of hierarchical structure formation, in which small structures form before larger ones, clusters belong to the youngest objects and still contain important information on the initial density perturbations from which they originate. Clusters consist of three main components: galaxies, a hot optical thin X-ray emitting thermal plasma (intracluster medium --ICM), and dark matter. Since clusters are dominated by dark matter they provide a unique opportunity to study this kind of material via its gravitational forces and its distribution in the cluster. The baryon fraction in clusters is similar to the one found throughout the universe. With information on primordial nucleosynthesis, which gives constraints on the baryon density $\Omega_b$ in the universe, it is possible with the baryon fraction measured in clusters to give constraints on the cosmological density parameter $\Omega_m$, which gives typical values of $\Omega_m=0.2-0.4$. Clusters grow by merging with other groups of galaxies or clusters, which is coupled to the global matter distribution in the universe and large scale structure formation in general. The ICM is an ideal tracer for merging processes in clusters and allows via its density and temperature distribution to reconstruct recent merger history, which yields information on structure formation. Furthermore, the comparison of distant with nearby clusters allows to give constraints on the evolution of structure formation in the universe. Clusters show, as predicted from theory, a high degree of self-similarity, which indicates that our understanding of structure formation is largely correct. Above mentioned issues show that clusters are powerful tools to study cosmology and structure formation at the same time, which will be outlined in more detail in the work presented here.
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https://tel.archives-ouvertes.fr/tel-00005346
Contributor : Doris Neumann <>
Submitted on : Friday, March 26, 2004 - 2:22:17 PM
Last modification on : Monday, February 10, 2020 - 6:12:38 PM
Long-term archiving on: : Monday, September 6, 2010 - 11:41:10 AM

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• HAL Id : tel-00005346, version 1

### Citation

Doris Neumann. Les amas de galaxies: des outiles pour etudier la formation des structures et la cosmologie. Astrophysique [astro-ph]. Université Paris-Diderot - Paris VII, 2003. ⟨tel-00005346⟩

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