A combined optical/X-ray study of the Galaxy cluster Abell 2256

The Astrophysical Journal1989Vol. 336, pp. 77–77

Citations Over TimeTop 10% of 1989 papers

Daniel G. Fabricant, S. Kent, Michael J. Kurtz

Abstract

The dynamics of Abell 2256 (z = 0.06) are investigated by combining X-ray observations of the intracluster gas with optical observations of the galaxy distribution and kinematics. We present magnitudes and positions for 172 galaxies and new redshifts for 75. Abell 2256 is similar to the Coma Cluster in its X-ray luminosity, mass, and galaxy density. Both the X-ray surface brightness and the galaxy surface density distributions exhibit an elliptical morphology. The radial galaxy distribution is steeper than the density profile of the X-ray-emitting gas, yet the galaxy velocity dispersion is higher than the equivalent value for the gas. Under the simplest assumptions that the galaxy velocity distribution is isotropic and the gas is isothermal, the galaxies and gas cannot be in hydrostatic equilibrium in a common gravitational potential. Self-consistent dynamical models can be constructed that are in agreement with the available X-ray and optical data; these models have the common features that the mass-to-light ratio increases with radius and that the galaxy orbits are anisotropic with a radial bias. We consider, in addition, the possibility that the high apparent line-of-sight galaxy velocity dispersion may be the result of substructure in the cluster, contamination by interloper galaxies, or an extremely flattened geometry. If any of the latter three situations pertained, there would be no need to invoke radially increasing mass-to-light ratios or anisotropic galaxy orbits.

Citations Over TimeTop 10% of 1989 papers

Abstract

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