Merging of Globular Clusters in Inner Galactic Regions. I. Do They Survive the Tidal Interaction?

Abstract

The main topic of this paper is the investigation of the modes of interaction of globular clusters (GCs) moving in the inner part of a galaxy. This is tackled by means of high-resolution N-body simulations, whose first results are presented in this article. Our simulations dealt with primordial, very massive (of the order of 107 Msolar) GCs that were able to decay, because of dynamical friction, into the inner regions of triaxial galaxies on a timescale much shorter than their internal relaxation time. To check the disruptive roles of both tidal forces and GC-GC collisions, their effects were maximized by considering clusters on quasi-radial orbits and choosing the initial conditions so as to give head-on collisions at each passage through the center. The available CPU resources allowed us to simulate clusters with different structural parameters and to follow them on quasi-radial orbits during eight passages across the center. The main findings are as follows: (1) clusters with an initial high-enough King concentration parameter (c>=1.2) preserve up to 50% of their initial mass, (2) the inner density distribution of the surviving clusters keeps a King model profile, (3) GC-GC collisions have a negligible effect compared with that caused by the passage through the galactic center, (4) the orbital energy dissipation due to the tidal interaction is of the same order as that caused by dynamical friction, (5) complex substructures like ``ripples'' and ``clumps'' are formed, as observed around real clusters. These findings support the validity of the hypothesis of merging of GCs in the galactic central region, with modes that deserve further careful investigation