Dark energy and the structure of the Coma cluster of galaxies

Context. We consider the Coma cluster of galaxies as a gravitationally bound physical system embedded in the perfectly uniform static dark energy background as implied by Lambda CDM cosmology. Aims. We ask if the density of dark energy is high enough to affect the structure of a large and rich cluster of galaxies. Methods. We base our work on recent observational data on the Coma cluster, and apply our theory of local dynamical effects of dark energy, including the zero-gravity radius R-ZG of the local force field as the key parameter. Results. 1) Three masses are defined that characterize the structure of a regular cluster: the matter mass M-M, the dark-energy effective mass M-DE (<0), and the gravitating mass M-G (=M-M + M-DE). 2) A new matter-density profile is suggested that reproduces the observational data well for the Coma cluster in the radius range from 1.4 Mpc to 14 Mpc and takes the dark energy background into account. 3) Using this profile, we calculate upper limits for the total size of the Coma cluster, R <= R-ZG approximate to 20 Mpc, and its total matter mass, M-M less than or similar to M-M(R-ZG) = 6.2 x 10(15) M-circle dot. Conclusions. The dark energy antigravity affects the structure of the Coma cluster strongly at large radii R greater than or similar to 14 Mpc and should be considered when its total mass is derived.