The Fundamental Straight Line of Galactic Globular Clusters

A detailed analysis of the Fundamental Plane properties of Globular Cluster is performed. If a sample of ordinary King-model clusters is considered, it is found that, in the "S-space" defined by the parameters (log r_c, log sigma_0, mu_V(0)), their configuration is similar to a straight line. It is shown that, with rather simple assumptions, a simultaneous explanation of all the observed correlations between S-space parameters can be provided. It is suggested that, at earlier times, Globular Clusters populated a line in the three-dimensional S-space, i.e. their original dynamical structure was fully determined by a single physical parameter.