THE GALACTIC GLOBULAR-CLUSTER SYSTEM

We explore correlations between various properties of Galactic globula r clusters, using a database on 143 objects. Our goal is identify corr elations and trends which can be used to test and constrain theoretica l models of cluster formation and evolution. We use a set of 13 cluste r parameters, 9 of which are independently measured. Several arguments suggest that the number of clusters still missing in the obscured reg ions of the Galaxy is of the order of 10, and thus the selection effec ts are probably not severe for our sample. Known clusters follow a pow er-law density distribution with a slope similar to-3.5 to -4, and an apparent core with a core radius similar to 1 kpc. Clusters show a lar ge dynamical range in many of their properties, more so for the core p arameters (which are presumably more affected by dynamical evolution) than for the half-light parameters. There are no good correlations wit h luminosity, although more luminous clusters tend to be more concentr ated. When data are,binned in luminosity, several trends emerge: more luminous clusters tend to have smaller and denser cores. We interpret this as a differential survival effect, with more massive clusters sur viving longer and reaching more evolved dynamical states. Cluster core parameters and concentrations also correlate with the position in the Galaxy, with clusters closer to the Galactic center or plane being mo re concentrated and having smaller and denser cores. These trends are more pronounced for the fainter (less massive) clusters. This is in an agreement with a picture where tidal shocks form disk or bulge passag es accelerate dynamical evolution of clusters. Cluster metallicities d o not correlate with any other parameter, including luminosity and vel ocity dispersion; the only detectable trend is with the position in th e Galaxy, probably reflecting Zinn's disk-halo dichotomy. This suggest s that globular clusters were not self-enriched systems. Velocity disp ersions show excellent correlations with luminosity and surface bright ness. Their origin is not well understood, but they may well reflect i nitial conditions of duster formation, and perhaps even be used to pro be the initial density perturbation spectrum on a similar to 10(6)M(ci rcle dot) scale. Core radii and concentrations play a role of a ''seco nd parameter'' in these correlations. While a global manifold of clust er properties has a high statistical dimensionality (D>4), a subset of structural, photometric, and dynamical parameters forms a statistical ly three-dimensional family, as expected from objects following King m odels; we propose to call this set of quantities the King Manifold. So me of the observed correlations may be usable as distance indicator re lations for globular clusters.