THE DYNAMICAL EQUILIBRIUM OF GALAXY CLUSTERS

If a galaxy cluster is effectively in dynamical equilibrium, then all galaxy populations within the cluster must have distributions in veloc ity and position that individually reflect the same underlying mass di stribution, although the derived virial masses can be quite different. Specifically, within the Canadian Network for Observational Cosmology cluster sample, the virial radius of the red galaxy population is, on the average, a factor of 2.05 +/- 0.34 smaller than that of the blue population. The red galaxies also have a smaller rms velocity dispersi on, a factor of 1.31 +/- 0.13 within our sample. Consequently, the vir ial mass calculated from the blue galaxies is 3.5 +/- 1.3 times larger than from the red galaxies. However, applying the Jeans equation of s tellar hydrodynamic equilibrium to the red and blue subsamples separat ely gives statistically identical cluster mass profiles. This is stron g evidence that these clusters are effectively equilibrium systems and therefore demonstrates empirically that the masses in the virialized region are reliably estimated using dynamical techniques.