Astronomy and Astrophysics – Astrophysics
Scientific paper
1995-07-10
Astronomy and Astrophysics
Astrophysics
13 pages, uuencoded gzipped postscript file, fig.1 available upon request, to appear in ApJ on 20th December 1995, corrected m
Scientific paper
10.1086/176711
Using a large and well-controlled sample of clusters of galaxies, we investigate the relation between cluster velocity dispersions and X-ray temperatures of intra-cluster gas. In order to obtain a reliable estimate of the total velocity dispersion of a cluster, independent of the level of anisotropies in galaxy orbits, we analyze the integrated velocity dispersion profiles over increasing distances from the cluster centers. Distortions in the velocity fields, the effect of close clusters, the presence of substructures, and the presence of a population of (spiral) galaxies not in virial equilibrium with the cluster potential are taken into account. Using our final sample of 37 clusters, for which a reliable estimate of the velocity dispersion could be obtained, we derive a relation between the velocity dispersions and the X-ray temperatures, with a scatter reduced by more than 30 % with respect to previous works. A chi square fit to the temperature-velocity dispersion relation does not exclude the hypothesis that the ratio between galaxy and gas energy density (the so-called spectral beta) is a constant for all clusters. In particular, the value of beta=1, corresponding to energy equipartition, is acceptable.
Biviano Andrea
Fadda Dario
Girardi Maria
Giuricin Giuliano
Mardirossian Fabio
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