Galactic evolution modeling

We present chemical evolution models for NGC 6822 computed with five fixed parameters, all constrained by observations, and only a free parameter, related with galactic winds. The fixed parameters are i) the infall history that has produced NGC 6822 is derived from its rotation curve and a cosmological model ii) the star formation history of the whole galaxy based on star formation histories for 8 zones inferred from H-R diagrams iii) the IMF, the stellar yields, and the percentage of Type la SNe progenitors are the same than those that reproduce the chemical history of the Solar Vicinity and the Galactic disk. 

Fig. 4.12. Stellar lithium abundances (log of the number per 1012 H atoms) among main-sequence stars as a function of metallicity. The full-drawn curve shows the prediction of a numerical Galactic chemical evolution model, while the broken-line curve gives the sum of a primordial component and an additional component proportional to iron and normalized to meteoritic abundance. Adapted from Matteucci, D Antona and Timmes (1995).

For a description of additional numerical Galactic chemical evolution models, as well as aspects of nucleosynthesis (e.g. from novae) not discussed in this book, see the monograph by Matteucci (2001). 

The model assumes that evolution takes place in a closed system, with successive generations of stars being bom into the interstellar medium. At each generation, a fraction of the gas is transformed into metals and returned to the interstellar medium. Gases imprisoned in stars of low mass and compact residues play no further role in galactic evolution. In this model, metaUicity is bound to increase as time goes by. And so the arrow of galactic time is defined. Evolution will continue until no further gas is available to form new stars. 

The whole art in the study of galactic evolution is to put forward a model that relates to available data, taking their volume and accuracy into account. Consequently, the evolutionary model must itself be conceived in an evolutionary way. 

In those years Soviet astronomers had the tradition to attend Caucasus Winter Schools. Our results of galactic mass modelling were reported in a Winter School in 1972. The next School was hold near the Elbrus mountain in a winter resort, in January 1974. The bottom line of my report was all giant galaxies have massive coronas, therefore dark matter must be the dominating component in the whole universe (at least 90 % of all matter). In the Winter School prominent Soviet astrophysicists as Zeldovich, Shklovsky, Novikov and others participated. In the discussion after the talk two questions dominated What is the physical nature of the dark matter and What is its role in the evolution of the Universe A detailed report of this study was sent to Nature (Einasto, Kaasik Saar 1974). 

Langevin systems of coupled nonlinear equations have been used recently in the modeling of galactic evolution, in the framework of the so-called... 

Langevin Systems Presented in the Literature for the Modeling of Galactic Evolution... 

In the foregoing sections we reviewed some stochastic models for stellar formation and galactic evolution widely employed in the literature. Here, we shall discuss expUdtly a simplified astrophysical model where the stochastic processes introduced for mimicking the complexity of the relevant interactions are dealt with by recourse to the analytical tools of the previous chapters in this volume (notably Grigolini and Marchesoni, Chapter II). 

Supplementary Parameters- Infall of extragalactic gas, radial flows and galactic winds are important ingredients in building galactic chemical evolution models. 

Theoretical models of galactic chemical evolution offer varying predictions of how the gradient should change with time, so using open clusters to measure that time-dependence can provide important constraints on model parameters. 

Abstract. The most recently discovered Galactic component - thick disk - still needs high-resolution spectral investigations since its origin and evolution is not understood enough. Elemental abundance ratios in the metallicity range —0.68 < [Fe/H] < —0.10 were determined in a sample of 10 thick-disk dwarfs and compared with results of other stars investigated as well as with models of thin disk chemical evolution. 

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