The structure of nearby clusters of galaxies

The analysis of the surface brightness distribution of the X-rays light from clusters of galaxies makes possible to obtain the ICM gas and temperature distributions and metal content as well as to estimate the entropy of clusters, which is a tracer of the thermodynamical history of these systems. The analysis of 24 relaxed Abell galaxy clusters in the redshift range 0.01 < z < 0.3, observed with ROSAT/PSPC, shows that the hot gas in all these clusters roughly has the same integrated specific entropy, although a second order correlation between this integrated specific entropy and both the gas mass and the dynamical mass is observed. Another interesting result is that a scaling law links the cluster potential energy to its total mass, with the same slope as that derived for elliptical galaxies and for dark matter halo simulations. Comparable relations are also obtained for the dark matter component. One of the main conclusions that comes out is that all these correlations are probably the consequence of the formation and evolution processes undergone by clusters of galaxies, containing information about the DM halo merging history and non-gravitational processes affecting the intra cluster gas. The fact that analogous correlations are observed for both elliptical galaxies and relaxed galaxy clusters suggests that formation processes affecting these self-gravitating systems are quite similar regardless the scale involved, and ellipticals can be considered as scaled down versions of clusters. See: Demarco et al. 2003, A&A, 407, 437, and references therein.

This work is the culmination of a study that was started as the research project required to obtain the Advanced Studies Diploma (DEA) in Astrophysics of the Université Denis Diderot (Paris 7). That project was carried out at the Institut d'Astrophysique de Paris (IAP), under the direction of Dr. F. Durret and Dr. D. Gerbal (See: dissertation; also see: Demarco et al. 2000).