Among the possible phenomena inducing evolution of the globular cluster system in an elliptical galaxy, dynamical friction due to field stars and tidal disruption caused by a central nucleus is of crucial importance. The aim of this paper is the study of the evolution of the globular cluster system in a triaxial galaxy in the presence of these phenomena. In particular, the possibility is examined that some galactic nuclei have been formed by frictionally decayed globular clusters moving in a triaxial potential. We find that the initial rapid growth of the nucleus, due mainly to massive clusters on box orbits falling in a short time scale into the galactic center, is later slowed by tidal disruption induced by the nucleus itself on less massive clusters in the way described by Ostriker, Binney, and Saha. The efficiency of dynamical friction is such to carry to the center of the galaxy enough globular cluster mass available to form a compact nucleus, but the actual modes and results of cluster-cluster encounters in the central potential well are complicated phenomena which remains to be investigated. The mass of the resulting nucleus is determined by the mutual feedback of the described processes, together with the initial spatial, velocity, and mass distributions of the globular cluster family. The effect on the system mass function is studied, showing the development of a low- and high-mass turnover even with an initially flat mass function. Moreover, in this paper is discussed the possibility that the globular cluster fall to the galactic center has been a cause of primordial violent galactic activity. An application of the model to M31 is presented

Nuclear star clusters (NSCs) are often present in spiral galaxies as well as resolved stellar nuclei (SNi) in elliptical galaxies centres. Ever growing observational data indicate the existence of correlations between the properties of these very dense central star aggregates and those of host galaxies, which constitute a significant constraint for the validity of theoretical models of their origin and formation. In the framework of the well-known ‘migratory and merger’ model for NSC and SN formation, in this paper we obtain, first, by a simple argument the expected scaling of the NSC/SN mass with both time and parent galaxy velocity dispersion in the case of dynamical friction as dominant effect on the globular cluster system evolution. This generalizes previous results by Tremaine et al. and is in good agreement with available observational data showing a shallow correlation between NSC/SN mass and galactic bulge velocity dispersion. Moreover, we give statistical relevance to predictions of this formation model, obtaining a set of parameters to correlate with the galactic host parameters. We find that the correlations between the masses of NSCs in the migratory model and the global properties of the hosts reproduce quite well the observed correlations, supporting the validity of the migratory-merger model. In particular, one important result is the flattening or even decrease of the value of the NSC/SN mass obtained by the merger model as function of the galaxy mass for high values of the galactic mass, i.e. ≳3 × 10¹¹ M_⊙, in agreement with some growing observational evidence.

We present results of fully self-consistent N-body simulations of the motion of four globular clusters moving in the inner region of their parent galaxy. With regard to previous simplified simulations, we confirm merging and formation of an almost steady nuclear cluster, in a slightly shorter time. The projected surface density profile shows strong similarity to that of resolved galactic nuclei. This similarity reflects also in the velocity dispersion profile which exhibits a central colder component as observed in many nucleated galaxies.

In this paper we present the results of two detailed N-body simulations of the interaction of a sample of four massive globular clusters in the inner region of a triaxial galaxy. A full merging of the clusters takes place, leading to a slowly evolving cluster which is quite similar to observed Nuclear Clusters. Actually, both the density and the velocity dispersion profiles match qualitatively, and quantitatively after scaling, with observed features of many nucleated galaxies. In the case of dense initial clusters, the merger remnant shows a density profile more concentrated than that of the progenitors, with a central density higher than the sum of the central progenitors central densities. These findings support the idea that a massive Nuclear Cluster may have formed in early phases of the mother galaxy evolution and lead to the formation of a nucleus, which, in many galaxies, has indeed a luminosity profile similar to that of an extended King model. A correlation with galactic nuclear activity is suggested.