We investigate the chemo-dynamical evolution of elliptical galaxies, to understand the origin of the mass-dependence of photometric properties such as the colour-magnitude relation (CMR). Our three-dimensional TREE N-body/SPH numerical simulation takes into account both Type II and Type Ia supernovae and follows the evolution of the abundances of several chemical elements. We derive the photometric properties of the simulation end-products and compare them with the observed CMR.

Dusty planetary disks can form quickly around young stars and linger, despite the depletion of dust through mechanisms such as Poynting-Robertson drag. Planetesimals in the disk can replenish the dust with an efficiency that depends on their mass and velocity distributions. Here, we describe a numerical program to track the evolution of planetesimals through merging, fragmentation and drag. Our current effort is focused on coupling a Fokker-Planck solver with N-body calculations to follow the detailed behavior of larger planetesimals. Our results demonstrate the importance of gravitational stirring in dust production. Furthermore, stirring by planets larger than Pluto can generate the large scale heights seen in several dusty disks.

We study the effects of the ultraviolet background radiation (UVB) on the formation of primordial galaxies, solving self-consistently radiative transfer of photons, non-equilibrium H2 chemistry, and one-dimensional hydrodynamics. The cut-off scale of collapse is shown to drop significantly compared to previous optically thin predictions, due to both self-shielding of the gas and H2 cooling. For plausible radiation intensities and spectra, the collapsing gas can cool efficiently to temperatures well below 104K before rotationally supported. Our results imply that star formation can take place in low-mass objects collapsing in the UVB.

We simulate the chemodynamical evolution of the Milky Way using our GRAPE-SPH code, and reproduce the age-metallicity relation, the [O/Fe]-[Fe/H] relation, and the metallicity distribution.

We followed Wielen's (1974) and Osipkov's, Kozhanov's (1986) procedure to derive the equation of motion of a cluster in the solar neighborhood in taking into account of a galactic tidal field, which is assume to have axial symmetry, and gravitational influence of spherical stellar clouds.

On the basic of this equations and using the linear approximation for the galactic field (Wielen 1974) one can derive virial equation of Jacobi for variable masses of stellar clusters. The non-stability by Lagrange condition, describing behavior of this system is obtained.

Observations of rich LMC clusters reveal an increasing spread in core radius with increasing age. We use N-body simulations of clusters on elliptical orbits about the LMC to show that a time-varying tidal field can result in significant core expansion. The observed spread in core radii may therefore reflect a spread in orbital parameters between clusters.

The Direct Simulation Monte Carlo (DSMC) method, developed originally to calculate rarefied gas dynamical problems, is applied to continuous flow including shocks assuming that the Knudsen number is sufficiently small. In particular, we study the formation of spiral shocks in the accretion disc of a close binary system. The method involves viscosity and thermal conduction automatically, and can thus simulate turbulent viscosity.

Results of 3D numerical simulations of the gas transfer in close binary systems show that it is possible the production of accretion streams having low specific angular momentum in a region close to the accreting star. These streams are mainly placed above the orbital disc. The eventual formation of such bulges and shock heated flows is interesting in the context of advection dominated solutions and for the explanation of spectral properties of the Black Hole candidates in binary systems. We set up a parallelized version of 3D S.P.H. code, using domain decomposion. with increasing spatial resolution around the compact star.

The formation and evolution of monopoles produced at TeV energy scales are considered. They can contribute to the generation of baryon number and may solve the cosmological problem. The dynamics of electroweak defects is completely different from that of conventional grand unification scale defects so that their number density should not be described by the scaling model.

In the current most plausible Cold Dark Matter (CDM) cosmology, larger halos increase their mass by the progressive mergers of smaller clumps. Due to these progressive merger events, galaxies have formed and evolved. Such merger events could trigger star bursts depending on mass of a merging object. In other words, star formation history reflects the strength of the interaction between a galaxy and merging objects. Also, a several merger events strongly affect the development of the morphology of galaxies as assumed in semi-analytic models. In the most advanced semi-analytic models, N-body simulations of dark matter particles are used to obtain the merging history of halos. By combining the description of radiative cooling, hydrodynamics and star formation with the obtained merging history, such models successfully have explained the various qualitative predictions. Here, we show the results of similar approach but using a fullly numerical model. In contrast to the semi-analytic models, we use our high resolution Smoothed Particle Hydrodynamics (SPH) models. With our SPH code, we try to tackle the problem of the galaxy morphology. We have done a several handful high-resolution SPH simulations and analyzed the merging history of such models. Accordingly, we can see the relation between the obtained morphology and the merging history or other physical properties of the model.

The relaxation time of a spherical galaxy with various density distributions has been evaluated using numerical simulations. The results indicate that the relaxation time is weakly dependent on the density of the galaxies in these simulations.

Using a combination of a cosmological N-body simulation and a semi-analytic galaxy formation model, we investigate environmental effects on cluster galaxies with the ACDM cosmology. We find that stripping of hot gas from galacitc halos as they infall into larger objects sufficiently suppresses star formation in the cluster and successfully reproduces the observed gradients of SFR when we normalize our model to reproduce the observed properties of local galaxies. Consequently, the effect of ram-pressure stripping of cold gas from galactic disks becomes quite small and it is observationally negligible. Therefore, the deficiency of galaxies with intermediate bulge-to-disk luminosity ratios under the hierarchical structure formation cannot be resolved even if we include the ram-pressure stripping in our modeling.

We investigate the orbital behavior in a class of analytic potentials in order to isolate the families of orbits which lead to the appropriate appearance of boxy/peanut features. This is the first step towards understanding the orbits of particles in N-body simulations of barred galaxies. Our final goal is to find out which dynamical mechanisms determine the peanut or boxy shapes.

We report on the development of a N-body/SPH code for galaxy interactions, with particular emphasis on SN feedback implementations. We show that current methods of SN feedback probably need simulations with > 105 – 106 gas particles per galactic disk to be able to realistically describe galactic fountains and superwinds.

We study cloud mass function (here after CMF) obtained in a Grape-SPH simulation of model galaxy. The CMF can be fitted by a simple power law, and its power law index is ∼ −2.0, which closes to the observational results.

It is likely that cold molecular clouds formed early, even before galaxies. In this work, we try to assess the consequences of using cold fractal gas for disc formation instead of hot gas, with a focus on angular momentum loss through dynamical friction. Using numerical simulations, we show that the dynamical friction from the dark matter halo on the cold gas fractal structures is not affected by the morphology of the structures, but is affected by their dynamical nature: their deformations and fluctuations. We argue that for typical values of the physical parameters during disc formation, the friction at small scale is reduced.

In most of globular clusters, surface abundance anomalies are observed not only from red giant stars but also from main sequence stars. We discuss the possibility that the latter anomalies can be explained in terms the pollution due to mass transfer during close encounters with red giants, the latter of which have already developed the anomalies through their internal processes. If this is the case, the main sequence stars with the abundance anomalies may serve as a probe into the star-star interactions in dense cores of globular clusters.

We calculate some indicators, which are closely related with galaxy clusters' substructure, for each cluster obtained in numerical simulations in OCDM and ΓCDM, and make a statistical comparison between two models. In ΓCDM the indicators, multipole moment power ratios and center shifts, are larger than those in OCDM. This result is consistent with the analytical prediction; galaxy clusters' formation epoch in ΓCDM is later than in OCDM and then clusters in OCDM are more relaxed than those in ΓCDM. We show that these indicators for X-ray surface brightness are useful tools to distinguish between OCDM and ΓCDM.

We investigate the dynamical evolution of clusters of galaxies in virial equilibrium by using Fokker–Planck models and self-consistent N-body models. In particular we focus on the growth of the common halos and the development of the central density cusps in the clusters. We find good agreement between the Fokker–Planck and N-body models. At the cluster center the cusp approximated by a power law, ρ(r) ∝ r-α (α ∼ 1), develops. We conclude that this shallow cusp results from the combined effects of two-body relaxation and tidal stripping. The cusp steepness α weakly depends on the relative importance of tidal stripping.

We performed N-body simulations of dense particulate disks and quantitatively analyzed angular momentum transfer processes therein. Angular momentum transfer is dominated by both gravitational torque and particles' collective motion associated with the structure. These processes depend on surface density, and do not depend on particle size or number if the structure is resolved enough.