G. Hensler

Modeling the Evolution of Disk Galaxies. I. The Chemodynamical Method and the Galaxy Model

Here we present our two-dimensional chemodynamical code CoDEx, which we developed for the purpose of modeling the evolution of galaxies in a self-consistent manner. The code solves the hydrodynamical and momentum equations for three stellar components and the multiphase interstellar medium (clouds and intercloud medium), including star formation, Type I and Type II supernovae, planetary nebulae, stellar winds, evaporation and condensation, drag, cloud collisions, heating and cooling, and stellar nucleosynthesis. These processes are treated simultaneously, coupling a large range in temporal and spatial scales, to account for feedback and self-regulation processes, which play an extraordinarily important role in the galactic evolution. The evolution of galaxies of different masses and angular momenta is followed through all stages from the initial protogalactic clouds until now. In this first paper we present a representative model of the Milky Way and compare it with observations. The capability of chemodynamical models is convincingly proved by the excellent agreement with various observations. In addition, well-known problems (the G-dwarf problem, the discrepancy between local effective yields, etc.), which so far could be only explained by artificial constraints, are also solved in the global scenario. Starting from a rotating protogalactic gas cloud in virial equilibrium, which collapses owing to dissipative cloud-cloud collisions, we can follow the galactic evolution in detail. Owing to the collapse, the gas density increases, stars are forming, and the first Type II supernovae explode. The collapse time is 1 order of magnitude longer than the dynamical free-fall time because of the energy release by Type II supernovae. The supernovae also drive hot metal-rich gas ejected from massive stars into the halo, and as a consequence, the clouds in the star-forming regions have lower metallicities than the clouds in the halo. The observed negative metallicity gradients do not form before t = 6 × 109 yr. These outward gas flows prevent any clear correlation between local star formation rate and enrichment and also prevent a unique age-metallicity relation. The situation, however, is even more complicated, because the mass return of intermediate-mass stars (Type I supernovae and planetary nebulae) is delayed depending on the type of precursor. Since our chemodynamical model includes all these processes, we can calculate, e.g., the [O/H] distribution of stars and find good agreement everywhere in bulge, disk, and halo. From the galactic oxygen to iron ratio, we can determine the supernovae ([II + Ib]/Ia) ratio for different types of Type Ia supernovae (such as carbon deflagration or sub-Chandrasekhar models) and find that the ratio should be in the range 1.0-3.8. The chemodynamical model also traces other chemical elements (e.g., N + C), density distributions, gas flows, velocity dispersions of the stars and clouds, star formation, planetary nebula rates, cloud collision, condensation and evaporation rates, and the cooling due to radiation. The chemodynamical treatment of galaxy evolution should be envisaged as a necessary development, which takes those processes into account that affect the dynamical, energetical, and chemical evolution.

Evolution of dwarf-elliptical galaxies

Here we present as an extension to already published models of massive spherical galaxies one-dimensional chemo-dynamical models of dwarf elliptical galaxies in the mass range between 10 9 and 10 10 xa0

Hot halo gas in the Virgo cluster galaxy NGC 4569

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The Exceptionally Soft X-Ray Spectrum of the Low-Mass Starburst Galaxy NGC 1705

u2000and initial density fluctuation of 1 σ and 3 σ . Because of their vanishing angular momentum the models are restricted to spherical symmetry. Due to this limitation the dynamics of the different components consider only radial motions and also their interaction processes have only one degree of freedom. Therefore, the galaxy evolution is preferably determined by radial oscillatory phenomena caused by heating and cooling of the interstellar gas, which reenforce effects like starbursts. Nevertheless, the low gravitational binding energy of dwarf ellipticals can easily be exceeded by thermal and turbulent energy production in the interstellar medium, leading to gas expansion and even to galactic winds. Furthermore, gas phases as well as gas and stars can decouple dynamically during the galactic evolution. For comparison with observational signatures like stellar kinematics, radial densities and metallicity distributions of the different components, the chemo-dynamical treatment of galaxy evolution must take the multi-phase character of the interstellar medium and self-regulation of star formation at low gravitation into account. Since non-rotating low-mass galaxies with stochastic star-formation episodes are seen as dwarf ellipticals, the aim of this paper is to compare the 1d chemo-dynamical models with observed characteristics of this type of dwarf galaxies. Several features like stellar populations from separate formation episodes, low metallicities, significant mass loss, etc. can be reproduced by the models in a global manner. Quantitative disagreements between model predictions and observations provide insight into necessary improvements of subsequent chemo-dynamical models implying rotation, dark matter halos, and external effects by an intergalactic gas, like its pressure, gas infall and stripping of galactic gas. The results can be summarized as follows: 10 9 xa0

A Multi-Phase Chemo-Dynamical SPH Code for Galaxy Evolution

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Physical Processes in Star–Gas Systems

u2000models are characterised by a single star-formation event during the initial collapse with an active self-regulation leading to reexpansion and massive gas loss as well as remaining at very low metallicities; 10 10 xa0

An X-ray halo in the "hot-spot" galaxy NGC 2903

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A multi-phase chemo-dynamical SPH code for galaxy evolution. Testing the code

u2000dwarf elliptical models become almost gas-free due to large initial star formation and a strong galactic wind. These as well as a

Gas Mixing, Gas Cycles and the Chemical Evolution of Dwarf Irregular Galaxies

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Chemodynamical Modelling of Galaxy Formation and Evolution

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