N-body computations of the action of dynamical friction on globular clusters

Numerical computations have been performed to study the action of dynamical friction on globular clusters in galaxies. Over a Hubble time, the distribution of globular clusters can be altered significantly by the action of dynamical friction which leads to the destruction of massive globular clusters in galaxies. We investigated the orbital decay rates for globular clusters in elliptical and spiral galaxies separately and compared the tv.10 decay rates to check whether dynamical friction is responsible for the difference observed in the luminosity functions for globular clusters in these types of ga.1J ..ax• 1es, in the sense that more massive globular clusters are observed in ellipticals than in spirals. Chapter one of the thesis discusses the determination of extra-galactic distances by using globular clusters, based on the assumption that the luminosity function of these systems is invariant throughout the universe. We also show the evaluation of the Hubble constant H , from the distance determined to the Virgo 0 cluster in this way. There are no compelling reasons to expect the luminosity function of the globular clusters to be the same in galaxies of all types and we report recent observations of the differences seen in the luminosity functions in elliptical and spiral globular cluster systems. The mechanisms which might lead to this difference are discussed and it is concluded here that dynamical friction might be the possible mechanism for the depletion of massive globular clusters in spiral galaxies. Chapter two reviews and discusses the theory and formulation of dynamical friction in detail. The third chapter is concerned with the finding of a suitable numerical integrator to solve the equations of motion in our N-body calculations. Various algorithms fJJere checked and tested for efficiency, stability and accuracy, in particular, Aarsethrs N-body code. We finally chose a second-order predictor corrector c Hybrid method ) for our restricted N-body code. Chapter four deals with the galaxy models, initial conditions for the particles that trace the density distributions in our galaxies and the globular cluster models that go into the N-body calculations. In chapter five, we discuss the numerical work for globular clusters orbiting in spiral galaxies. Preliminary results show that resonances play an important role in the.orbital evolution of the globular cluster. The slow orbital decay rates we have obtained indicated that dynamical friction is not enough to account for the observed depletion of massive globular clusters in spirals. Chapter six deals with the numerical work on globular clusters in ellipticals. We did not observe much decay in the orbits for these globular clusters, compared to the decay rates of clusters in spirals. In chapter seven, conclusions about this work and outlines for future work are sketched.