Roberto Capuzzo-Dolcetta

DISSIPATIONLESS FORMATION AND EVOLUTION OF THE MILKY WAY NUCLEAR STAR CLUSTER

In one widely discussed model for the formation of nuclear star clusters (NSCs), massive globular clusters spiral into the center of a galaxy and merge to form the nucleus. It is now known that at least some NSCs coexist with supermassive black holes (SMBHs); this is the case, for instance, in the Milky Way. In this paper, we investigate how the presence of an SMBH at the center of the Milky Way impacts the merger hypothesis for the formation of its NSC. Starting from a model consisting of a low-density nuclear stellar disk and the SMBH, we use direct N-body simulations to follow the successive inspiral and merger of globular clusters. The clusters are started on circular orbits of radius 20 pc, and their initial masses and radii are set up in such a way as to be consistent with the galactic tidal field at that radius. These clusters, decayed orbitally in the central region due to their large mass, were followed in their inspiral events; as a result, the total accumulated mass by ≈10 clusters is about 1.5 × 107 M ☉. Each cluster is disrupted by the SMBH at a distance of roughly 1 pc. The density profile that results after the final inspiral event is characterized by a core of roughly this radius and an envelope with density that falls off ρ ~ r –2. These properties are similar to those of the Milky Way NSC, with the exception of the core size, which in the Milky Way is somewhat smaller. But by continuing the evolution of the model after the final inspiral event, we find that the core shrinks substantially via gravitational encounters in a time (when scaled to the Milky Way) of 10 Gyr as the stellar distribution evolves toward a Bahcall-Wolf cusp. We also show that the luminosity function of the Milky Way NSC is consistent with the hypothesis that 1/2 of the mass comes from old (~10 Gyr) stars, brought in by globular clusters, with the other half due to continuous star formation. We conclude that a model in which a large fraction of the mass of the Milky Way NSC is due to infalling globular clusters is consistent with existing observational constraints.

The evolution of the globular cluster system in a triaxial galaxy : can a galactic nucleus form by globular cluster capture ?

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

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.

A fully parallel, high precision, N-body code running on hybrid computing platforms

We present a new implementation of the numerical integration of the classical, gravitational, N-body problem based on a high order Hermites integration scheme with block time steps, with a direct evaluation of the particle-particle forces. The main innovation of this code (called HiGPUs) is its full parallelization, exploiting both OpenMP and MPI in the use of the multicore Central Processing Units as well as either Compute Unified Device Architecture (CUDA) or OpenCL for the hosted Graphic Processing Units. We tested both performance and accuracy of the code using up to 256GPUs in the supercomputer IBM iDataPlex DX360M3 Linux Infiniband Cluster provided by the Italian supercomputing consortium CINECA, for values of N=<8millions. We were able to follow the evolution of a system of 8million bodies for few crossing times, task previously unreached by direct summation codes.

HENIZE 2-10: THE ONGOING FORMATION OF A NUCLEAR STAR CLUSTER AROUND A MASSIVE BLACK HOLE

The central region of the galaxy Henize 2-10 has a central black hole (BH) with a mass of about

DYNAMICAL FRICTION IN CUSPY GALAXIES

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A criterion for the choice of the interpolation kernel in smoothed particle hydrodynamics

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Globular Cluster System erosion in elliptical galaxies

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A Performance Comparison of Different Graphics Processing Units Running Direct N-Body Simulations

. While this black hole does not appear to coincide with any central stellar over density, it is surrounded by 11 young massive clusters with masses above

A Comparison between the Fast Multipole Algorithm and the Tree-Code to Evaluate Gravitational Forces in 3-D

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