GRAPE-SPH Chemodynamical Simulation of Elliptical Galaxies I: Evolution of Metallicity Gradients

We simulate the formation and chemodynamical evolution of 124 elliptical galaxies by using a GRAPE-SPH code that includes various physical processes associated with the formation of stellar systems: radiative cooling, star formation, feedback from Type II and Ia supernovae and stellar winds, and chemical enrichment. In our CDM-based scenario, galaxies form through the successive merging of sub-galaxies with various masses. Their merging histories vary between a major merger at one extreme, and a monolithic collapse of a slow-rotating gas cloud at the other extreme. The basic processes driving the evolution of the metallicity gradients are as follows: i) destruction by mergers to an extent dependent on the progenitor mass ratio. ii) regeneration when strong central star formation is induced at a rate dependent on the gas mass of the secondary. iii) slow evolution as star formation is induced in the outer regions through late gas accretion. We succeed in reproducing the observed variety of the radial metallicity gradients. The average gradient dlog Z/dlog r ~ -0.3 with dispersion of +- 0.2 and no correlation between gradient and galaxy mass are consistent with observations of Mg2 gradients. The variety of the gradients stems from the difference in the merging histories. Galaxies that form monolithically have steeper gradients, while galaxies that undergo major mergers have shallower gradients. Thus merging histories can, in principle, be inferred from the observed metallicity gradients of present-day galaxies. The observed variation in the metallicity gradients cannot be explained by either monolithic collapse or by major merger alone. Rather it requires a model in which both formation processes arise, such as the present CDM scheme.Comment: Accepted for publication in MNRAS. 21 pages, 14 figures, some color. mpeg simulations available at http://www.MPA-Garching.MPG.DE/~chiaki/movie.htm

GRAPE-SPH Chemodynamical Simulation of Elliptical Galaxies II: Scaling Relations and the Fundamental Plane

We simulate the formation and chemodynamical evolution of 128 elliptical galaxies using a GRAPE-SPH code that includes various physical processes that are associated with the formation of stellar systems: radiative cooling, star formation, feedback from Type II and Ia supernovae and stellar winds, and chemical enrichment. We find that the star formation timescale controls when and where stars form in the contracting gas cloud, determines the effective radius at given mass, and is constrained by observation to be ten times longer than the local dynamical timescale. We succeed in reproducing the observed global scaling relations under our CDM-based scenario, e.g., the Faber-Jackson relation, the Kormendy relation, and the fundamental plane. An intrinsic scatter exists along the fundamental plane, and the origin of this scatter lies in differences in merging history. Galaxies that undergo major merger events tend to have larger effective radii and fainter surface brightnesses, which result in larger masses, smaller surface brightnesses, and larger mass-to-light ratios. We can also reproduce the observed colour-magnitude and mass-metallicity relations, although the scatter is larger than observed. The scatter arises because feedback is not very effective and star formation does not terminate completely in our simulations. ~25% of accreted baryons are blown away in the simulations, independent of the assumed star formation timescale and initial mass function. Most heavy elements end up locked into stars in the galaxy. The ejected metal fraction depends only on the star formation timescale, and is ~2% even to rapid star formation.Comment: Accepted for publication in MNRAS. 13 pages mpeg simulations available at http://www.MPA-Garching.MPG.DE/~chiaki/movie.htm

Simulations of Cosmic Chemical Enrichment with Hypernova

We simulate cosmic chemical enrichment with a hydrodynamical model including supernova and hypernova feedback. We find that the majority of stars in present-day massive galaxies formed in much smaller galaxies at high redshifts, despite their late assembly times. The hypernova feedback drives galactic outflows efficiently in low mass galaxies, and these winds eject heavy elements into the intergalactic medium. The ejected baryon fraction is larger for less massive galaxies, correlates well with stellar metallicity. The observed mass-metallicity relation is well reproduced as a result of the mass-dependent galactic winds. We also predict the cosmic supernova and gamma-ray burst rate histories.Comment: Proceedings of the CRAL-Conference Series I "Chemodynamics: from first stars to local galaxies

The Derivation of the Exact Internal Energies for Spin Glass Models by Applying the Gauge Theory to the Fortuin-Kasteleyn Representation

We derive the exact internal energies and the rigorous upper bounds of specific heats for several spin glass models by applying the gauge theory to the Fortuin-Kasteleyn representation which is a representation based on a percolation picture for spin-spin correlation. The results are derived on the Nishimori lines which are special lines on the phase diagrams. As the spin glass models, the +-J Ising model and a Potts gauge glass model are studied. The present solutions agree with the previous solutions. The derivation of the solutions by the present method must be useful for understanding the relationship between the percolation picture for spin-spin correlation and the physical quantities on the Nishimori line.Comment: 10 pages, no figures. v3: minor corrections/addition

Proposal of a Checking Parameter in the Simulated Annealing Method Applied to the Spin Glass Model

We propose a checking parameter utilizing the breaking of the Jarzynski equality in the simulated annealing method using the Monte Carlo method. This parameter is based on the Jarzynski equality. By using this parameter, to detect that the system is in global minima of the free energy under gradual temperature reduction is possible. Thus, by using this parameter, one is able to investigate the efficiency of annealing schedules. We apply this parameter to the +-J Ising spin glass model. The application to the Gaussian Ising spin glass model is also mentioned. We discuss that the breaking of the Jarzynski equality is induced by the system being trapped in local minima of the free energy. By performing Monte Carlo simulations of the +-J Ising spin glass model and a glassy spin model proposed by Newman and Moore, we show the efficiency of the use of this parameter.Comment: 14 pages, 2 figures. v6: this is the final versio