DESTRUCTION OF THE GALACTIC GLOBULAR-CLUSTER SYSTEM

We investigate the dynamical evolution of the Galactic globular cluste r system in considerably greater detail than has been done hitherto, f inding that destruction rates are significantly larger than given by p revious estimates. The general scheme (but not the detailed implementa tion) follows Aguilar Hut, & Ostriker. For the evolution of individual clusters, we use a Fokker-Planck code including the most important ph ysical processes governing the evolution: two-body relaxation, tidal t runcation of clusters, compressive gravitational shocks while clusters pass through the Galactic disk, and tidal shocks due to passage close to the bulge. Gravitational shocks are treated comprehensively, using a recent result by Kundic & Ostriker that the (Delta E(2)) shock-indu ced relaxation term, driving an additional dispersion of energies, Is generally more important than the usual energy shift term (Delta E). V arious functional forms of the correction factor are adopted to allow for the adiabatic conservation of stellar actions in a presence of tra nsient gravitational perturbation. We use a recent compilation of the globular cluster positional and structural parameters, and a collectio n of radial velocity measurements. Two transverse to the line-of-sight velocity components were assigned randomly according to the two kinem atic models for the cluster system (following the method of Aguilar, H ut, & Ostriker): one with an isotropic peculiar velocity distribution, corresponding to the present-day cluster population, and the other wi th the radially preferred peculiar velocities, similar to those of the stellar halo. We use the Ostriker & Caldwell and the Bahcall, Schmidt , & Soneira models for our Galaxy. For each cluster in our sample, we calculated its orbits over a Hubble time, starting from the present ob served positions and assumed velocities. Medians of the resulting set of peri- and apogalactic distances and velocities are used then as an input for the Fokker-Planck code. Evolution of the cluster is followed up to its total dissolution due to a coherent action of all of tile d estruction mechanisms. The rate of destruction is then obtained as a m edian over all the cluster sample, in accord with Aguilar, Hut, & Ostr iker. We find that the total destruction rate is much larger than that given by Aguilar, Hut, & Ostriker with more than half of the present clusters (52%-58% for the Ostriker & Caldwell model, and 75%-86% for t he Bahcall, Schmidt, & Soneira model) destroyed in the next Hubble tim e. Alternatively put, the typical time to destruction is comparable to the typical age, a result that would follow from (but is not required by) an initially power law distribution of destruction times. We disc uss some implications for a past history of the globular cluster syste m and the initial distribution of the destruction times, raising the p ossibility that the current population is but a very small fraction of the initial population with the remnants of the destroyed clusters co nstituting presently a large fraction of the spheroid (bulge + halo) s tellar population.