A. Vicari

Self-consistent Models of Cuspy Triaxial Galaxies with Dark Matter Halos

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.

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

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 M☉) 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.

Large-scale star formation in galaxies - II. The spirals NGC 3377A, NGC 3507 and NGC 4394. Young star groupings in spirals

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, their surface luminosity density radial behaviour, are presented and comparatively discussed. These data, in addition to those in Paper I, constitute a first sample suitable for seeking correlations among properties of galaxies and their YSG, which we briefly discuss here.