6,340 research outputs found
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
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