We have constructed realistic, self-consistent models of triaxial elliptical galaxies embedded in triaxial dark matter halos. We examined three different models for the shape of the dark matter halo: (1) with the same axis ratios as the luminous matter (0:7 : 0:86 : 1), (2) with a more prolate shape (0:5 : 0:66 : 1), and (3) with a more oblate shape (0:7 : 0:93 : 1). Self-consistent solutions by means of the standard orbital superposition technique introduced by Schwarzschild were found in each of the three cases. The equilibrium velocity distribution is reproduced by a Lorentzian function better than by a Gaussian. Chaotic orbits were found to be important in all of the models, and their presence was shown to imply a possible slow evolution of the shapes of the halos. Our results demonstrate for the first time that triaxial dark matter halos can coexist with triaxial galaxies.

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 (order of 10 7 M ⊙ ) GCs that were able to decay, because of dynamical friction, into the inner regions of triaxial galaxies on a time much shorter than their internal relaxation time. To check the disruptive roles of both tidal forces and GC-GC collisions, their effects were maximised 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 8 passages across the center. The main findings are: i) clusters with an initial high enough King concentration parameter (c ≥ 1.2), preserve up to 50% of their initial mass; ii) the inner density distribution of the survived clusters keep a King model profile; iii) GC-GC collisions have a negligible effect with respect to that caused by the passage through the galactic center; iv) the orbital energy dissipation due to the tidal interaction is of the same order of that caused by dynamical friction; v) complex sub-structures like "ripples" and "clumps" 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 investigations.

The present work extends and deepens previous examinations of the evolution of globular cluster orbits in elliptical galaxies, by means of numerical integrations of a wide set of orbits in five self-consistent triaxial galactic models characterized by a central core and different axial ratios. These models are valid and complete in the representation of regular orbits in elliptical galaxies. Dynamical friction is definitely shown to be an efficient cause of evolution for the globular cluster systems in elliptical galaxies of any mass or axial ratio. Moreover, our statistically significant sample of computed orbits confirms that the globular cluster orbital decay times are, at least for clusters moving on box orbits, much shorter than the age of the galaxies. Consequently, the mass carried into the innermost galactic region in the form of decayed globular clusters may have contributed significantly to feeding and accreting a compact object therein

Coalescing binary black holes experience a ''kick'' due to anisotropic emission of gravitational waves with an amplitude as great as $200 km s À1 . We examine the orbital evolution of black holes that have been kicked from the centers of triaxial galaxies. Timescales for orbital decay are generally longer in triaxial galaxies than in equivalent spherical galaxies, since a kicked black hole does not return directly through the dense center where the dynamical friction force is highest. We evaluate this effect by constructing self-consistent triaxial models and integrating the trajectories of massive particles after they are ejected from the center; the dynamical friction force is computed directly from the velocity dispersion tensor of the self-consistent model. We find return times that are several times longer than in a spherical galaxy with the same radial density profile, particularly in galaxy models with dense centers, implying a substantially greater probability of finding an off-center black hole.

Abstract. The identification of young star groupings (YSG) in the three spiral galaxies NGC 3377A, NGC 3507, NGC 4394 is obtained by mean of the statistical method described in Paper I. We find 83, 90, 185 YSGs, respectively. An identification map of YSGs, as well as their size distribution, their B-luminosity function and their surface luminosity density radial behaviour are presented and compared. These data, in addition to those in Paper I, constitute a first sample suitable for seeking correlations among properties of galaxies and their YSGs, which we briefly discuss here.