arXiv subjects

R. Capuzzo-Dolcetta

Publications and source records attributed to R. Capuzzo-Dolcetta.

At least 55 records · Page 3Linked to original sources

arXiv2006

Galactic nuclei formation and activity induced by globular cluster merging

Different types of observations, together with consistent and physical modelizations, suggest as realistic the hypothesis of enrichement of galactic nuclei by mean of massive globular clusters orbitally decayed and merged in the inner regions of early type galaxies. In this context, the scenario of globular cluster mergers and subsequent formation of a dense Super Star Cluster in the center of a triaxial galaxy is presented and discussed, together with its astrophysical implications, including that of massive black hole feeding and accretion in the center of a triaxial galaxy.

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arXiv2006

Self-consistent models of cuspy triaxial galaxies with dark matter haloes

We have constructed realistic, self-consistent models of triaxial elliptical galaxies embedded in triaxial dark matter haloes. We examined three different models for the shape of the dark matter halo: (i) the same axis ratios as the luminous matter (0.7:0.86:1); (ii) a more prolate shape (0.5:0.66:1); (iii) a more oblate shape (0.7:0.93:1). The models were obtained by means of the standard orbital superposition technique introduced by Schwarzschild. Self-consistent solutions were found in each of the three cases. 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 haloes. Our results demonstrate for the first time that triaxial dark matter haloes can co-exist with triaxial galaxies.

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arXiv2006

Globular Cluster System evolution in early type galaxies

Globular clusters (GCs) constitute a system which is evolving because of various interactions with the galactic environment. Evolution may be the explanation of many observed features of Globular Cluster Systems (GCSs); the different radial distribution of the GCS and the stellar component of early type galaxies is explained by dynamical friction and tidal effects, this latter acting both on the large scale (that of the bulge-halo stars) and on the small scale (that of the nucleus, often containing a central massive black hole). Merging of quickly orbitally decayed massive GCs leads to formation of a Super Star Cluster (SSC) which enriches the galactic nucleus and is a reservoire of mass-energy for a centrally located black hole

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arXiv2004

Dynamical friction on Globular Clusters in core-triaxial galaxies: is it a cause of massive black hole accretion?

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 5 self-consistent triaxial galactic models characterized by a central core and different axial ratios. These models constitute a valid and complete 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 and axial ratios. Moreover, our statistically significant sample of computed orbits confirm that the globular cluster orbital decay times are, in a wide range of realistic initial conditions, much shorter than the age of the galaxies. Consequently, the huge quantity of mass carried into the innermost galactic region in form of decayed globular clusters have likely contributed significantly in feeding and accreting a compact object therein.

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arXiv2004

Elliptical galaxy nuclei activity powered by infalling globular clusters

Globular cluster systems evolve, in galaxies, due to internal and external dynamics and tidal phenomena. One of the causes of evolution, dynamical friction, is responsible for the orbital decay of massive clusters into the innermost galactic regions. It is found that these clusters are effective source of matter to feed a central galactic black hole such to make it grow and shine as an AGN.

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arXiv2003

Super computers in astrophysics and High Performance simulations of self-gravitating systems

The modern study of the dynamics of stellar systems requires the use of high-performance computers. Indeed, an accurate modelization of the structure and evolution of self-gravitating systems like planetary systems, open clusters, globular clusters and galaxies imply the evaluation of body-body interaction over the whole size of the structure, a task that is computationally very expensive, in particular when it is performed over long intervals of time. In this report we give a concise overview of the main problems of stellar systems simulations and present some exciting results we obtained about the interaction of globular clusters with the parent galaxy.

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arXiv2001

The contribution of primordial globular clusters to the central galactic activity

Globular clusters in galaxies have a mutual feedback with the environment, which is tuned by their dynamical evolution. This feedback may be the explanation of various features of both the globular cluster system and the host galaxy. Relevant examples of these are the radial distribution of globulars and the violent initial activity of galaxies as AGN.

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arXiv2001

An efficient parallel tree-code for the simulation of self-gravitating systems

We describe a parallel version of our tree-code for the simulation of self-gravitating systems in Astrophysics. It is based on a dynamic and adaptive method for the domain decomposition, which exploits the hierarchical data arrangement used by the tree-code. It shows low computational costs for the parallelization overhead -- less than 4% of the total CPU-time in the tests done -- because the domain decomposition is performed 'on the fly' during the tree setting and the portion of the tree that is local to each processor 'enriches' itself of remote data only when they are actually needed. The performances of an implementation of the parallel code on a Cray T3E are presented and discussed. They exhibit a very good behaviour of the speedup (=15 with 16 processors and 10^5 particles) and a rather low load unbalancing (< 10% using up to 16 processors), achieving a high computation speed in the forces evaluation (>10^4 particles/sec with 8 processors).

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arXiv2001

Galactic nuclear activity induced by globular cluster merging

The interpretation of the difference observed between the radial distribution of globular clusters and that of halo-bulge stars in elliptical galaxies is discussed in terms of evolution of their globular cluster systems. I present a short summary of the evidence that dynamical evolution of globular cluster systems is not only able to explain the flattening of their distribution toward the galactic center, but also it may have played an important role on the primordial activity of the parent galaxy.

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arXiv2001

Evolution of globular cluster systems in three galaxies of the Fornax cluster

We studied and compared the radial profiles of globular clusters and of the stellar bulge component in three galaxies of the Fornax cluster observed with the WFPC2 of the HST. A careful comparative analysis of these distributions confirms that stars are more concentrated toward the galactic centres than globular clusters, in agreement with what was observed in many other galaxies. If the observed difference is the result of evolution of the globular cluster system sstarting from initial profiles similar to those of the halo--bulge stellar components, a relevant fraction of their mass (74%, 47%, 52% for NGC 1379, NGC 1399 and NGC 1404, respectively) is disappeared in the inner regions, likely contributing to the nuclear field population, local dynamics and high energy phenomena in the primeval life of the galaxy. An indication in favour of the evolutionary interpretation of the difference between the globular cluster system and stellar bulge radial profiles is given by the positive correlation we found between the value of the mass lost from the GCS and the central galactic black hole mass in the set of seven galaxies for which these data are available.

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arXiv2001

Application of an objective method for the identification of Young Star Groupings in spiral galaxies

We present some results of the application of our automatic technique for the identification of Young Star Groupings (YSGs) in spiral galaxies. In this report we discuss our new results for NGC 3377a and NGC 3507 together with previously published data of NGC 7217, NGC 1058 and UGC 12732. The aim of this ongoing research is to obtain a wide sample of homogeneous data for the study of the YSGs and their relationships with the properties of their parent galaxies, using only objective identifications.

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arXiv2000

On the use of a heterogeneous MIMD-SIMD platform to simulate the dynamics of globular clusters with a central massive object

The dynamics of a large stellar (globular) cluster containing N=128,000 stars has been simulated by a direct summation (O(N$^2$)) method by using a heterogeneous platform. Preliminary simulations have been carried out on model systems with and without the presence, in their center of mass, of a black hole whose mass has been varied from 0.02 to 0.1 times the total mass of the cluster. These simulations followed the evolution of the globular cluster in order to describe its dynamics over an interval of time sufficiently large respect to the internal crossing time. Computations have demonstrated that the platform heterogeneity, allowing a very efficient use of the computational resources, can be considered a key feature for sustaining large computational loads. Our results show that the massive object in the center of the cluster alters the surrounding star distribution very quickly; the following evolution is much slower as it occurs via two-body collisional relaxation.

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arXiv2000

Large scale star formation in galaxies. I. The spirals NGC 7217, NGC 1058 and UGC 12732

We present multiband photometric observations of three spiral galaxies selected in a sample suited for the study of young stellar groupings and their relationship with the parent galaxy and the galactic environment. Star forming regions have been identified using an objective technique based on a multivariate statistical analysis. Maps of young star groupings are given for each galaxy. The luminosity functions of the young star group populations show a remarkable similarity with a slope in the range -1.52 to -1.33 range. The size distributions peak around the classical 100pc value of the Local Group associations for two out of the three galaxies. NGC 1058 shows smaller associations (peak at about 50pc). The total number of young groups per unit B absolute luminosity of the galaxy is significantly greater in UGC 12732. The activity of star formation is in all three galaxies clearly stronger in the central regions.

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arXiv1999

A Criterion for the choice of the interpolation kernel in Smoothed Particle Hydrodynamics

We study the problem of the appropriate choice of the interpolating kernel to be used in the evaluation of gradients of functions. Such interpolation technique is often used in applications, e.g. it is typical for Smoothed Particle Hydrodynamics (SPH). We propose a minimization procedure for selecting kernels in n-dimensions, in the class of regular, normalizable, symmetric functions having finite moments up to a sufficiently high order; the method is valid when the kernel width is position-dependent and allows to recover conservation laws at the same order of approximation that SPH, as interpolation technique, has when the kernel size is constant.

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arXiv1998

The Role of Hydrogen on Mass Loss from Proto-Globular Clusters

This short report is concerned with the well known and not yet satisfactorily answered problem of the existence of two well distinct typical mass scales of primordial halo objects: solar size objects (halo field stars) and globular cluster size objects (10^5 solar masses and more). A likely possibility is that almost all the gaseous content of the halo fragmented into massive clouds, which, in their turn, recycled part of their gas to the environment in either a quiescent either a violent way. The modes and quantity of mass loss depends on thermodynamic properties of gas clouds, determined, in a zero-metal environment, mainly by hydrogenic components evolution and influence on the equation of state. It is logical to expect that, due to the different dynamical and thermodynamical conditions of the recycled gas, another typical fragmenting mass scale is settled.

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arXiv1998

Globular cluster system erosion and nucleus formation in elliptical galaxies

The radial distribution of globular clusters in galaxies is always less peaked to the centre than the halo stars'. Extending previous work to a sample of HST globular cluster systems in ellipticals, we evaluate the number of clusters lost to the galactic centre as the integrals of the difference between the observed globular cluster system distribution and the underlying halo light profile. It results that the initial populations of globular clusters were from 25% to 50% richer than now. This significant number of missing globular clusters supports the hypothesis that a large quantity of globular cluster mass in form of globular clusters decayed and destroyed has been lost to the galactic centres, where plausibly contributed to formation and feeding of a mas sive object therein. It is relevant noting that the observed correlation between the core radius of the globular cluster system and the parent galaxy luminosity can be interpreted as a result of evolution.

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arXiv1998

Parallelization of a Code for the Simulation of Self-gravitating Systems in Astrophysics. Preliminary Speed-up Results

We have preliminary results on the parallelization of a Tree-Code for evaluating gravitational forces in N-body astrophysical systems. For our Cray T3D/CRAFT implementation, we have obtained an encouraging speed-up behavior, which reaches a value of 37 with 64 processor elements (PEs). According to the Amdahl'law, this means that about 99% of the code is actually parallelized. The speed-up tests regarded the evaluation of the forces among N = 130,369 particles distributed scaling the actual distribution of a sample of galaxies seen in the Northern sky hemisphere. Parallelization of the time integration of the trajectories, which has not yet been taken into account, is both easier to implement and not as fundamental.

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arXiv1997

Gravitational Waves Generated by Globular Cluster Systems Collapse

According to the hypothesis that AGNs are massive black holes and the mass which feeds them is made of stars belonging to globular clusters frictionally decayed and tidally destroyed by the field of the central object, it is possible to give an estimate of the number and spectral characteristics of detectable gravitational wave impulses generated by the falling of such stars into the black hole. We find that the orbitating gravitational antenna LISA, should detect from 10 to 100 impulses per year.

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