Detection of Massive Tidal Tails around the Globular Cluster Pal 5 with SDSS Commissioning Data

摘要

Globular clusters are self-gravitating stellar systems that experience a time-varying tidal potential as they orbit through their parent galaxy. Their dynamical evolution is driven by internal effects such as stellar evolution, two-body relaxation and binary heating, and by external effects induced by the galactic force field, i.e., heating by tidal shocks during disk and bulge passages and tidal stripping. Both internal and external effects should lead to a permanent loss of cluster members and to the eventual dissolution of the cluster. The Galactic globular clusters observed today are believed to be survivors from an initially much more numerous population. They appear to be in various stages of evolution and dissolution, depending on their initial conditions and their galactic orbits (e.g., Cherno & Weinberg 1990, Djorgovsky & Meylan 1994). Numerical simulations predict that possibly as many as half of the present-day Galactic globulars will not survive for another Hubble time (Gnedin & Ostriker 1997). Observational conformation of the gradual dissolution of globular clusters and determination of their mass loss rates is important in itself, but can also shed light on the formation history and structure of the Galactic halo and provide constraints on the Galactic potential.