We examine the dynamics of the Hydra I galaxy cluster. This cluster has circularly symmetric galaxy and X-ray distributions, and a velocity histogram that is close to Gaussian. However, the velocity distribution of galaxies near the cluster center is very flat. Using various statistical tests, we calculate the probability that the observed velocities were drawn from a normal distribution, or from a set of spherical equilibrium models. Based on several of the tests, the data are inconsistent with the models at the ~2.4 σ level. We therefore consider the possibility that substructure is important in this cluster. We find that a model that is spherically symmetric at large radii, and clumpy at small radii, is more consistent with the kinematical data. The locations and velocities of the brighter cluster galaxies also lend support to this hypothesis. Such a model can also explain why Hydra I does not lie along the L_X_ - σ relation for galaxy clusters. We discuss an observing strategy for clusters that may enable some of the basic questions about the dynamics of these systems to be answered.
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Fitchett et al. (1988) studied this question.