Chemical Evolution Of Galaxies And Intracluster Medium
In this series of lectures I discuss the basic principles and the modelling of the chemical evolution of galaxies. In particular, I present models for the chemical evolution of the Milky Way galaxy and compare them with the available observational data. From this comparison one can infer important constraints on the mechanism of formation of the Milky Way as well as on stellar nucleosynthesis and supernova progenitors. Models for the chemical evolution of elliptical galaxies are also shown in
... are also shown in the framework of the two competing scenarios for galaxy formation: monolithic and hierachical. The evolution of dwarf starbursting galaxies is also presented and the connection of these objects with Damped Lyman-α systems is briefly discussed. The roles of supernovae of different type (I, II) is discussed in the general framework of galactic evolution and in connection with the interpretation of high redshift objects. Finally, the chemical enrichment of the intracluster medium as due mainly to ellipticals and S0 galaxies is discussed. Basic parameters of chemical evolution Galactic chemical evolution is the study of the evolution in time and space of the abundances of the chemical elements in the interstellar gas in galaxies. This process is influenced by many parameters such as the initial conditions, the star formation and evolution, the nucleosynthesis and possible gas flows. Here I describe each one separately: • Initial conditions-One can assume that all the initial gas out of which the galaxy will form is already present when the star formation process starts or that the gas is slowly accumulated in time. Then one can assume that the initial chemical composition of this gas is primordial (no metals) or that some pre-enrichment has already taken place (e.g. Population III stars). As we will see in the following, different assumptions are required for different galaxies. • The birthrate function-Stars form and die continuously in galaxies, therefore a recipe for star formation is necessary. We define the stellar birthrate function as the number of stars formed in the time interval dt and in the mass range dm as: where: is the star formation rate (SFR), and: is the initial mass function (IMF). The SFR is assumed to be only a function of time and the IMF only a function of mass. This is clearly an oversemplification but is necessary in absence of a clear knowledge of the star formation process. • Stellar evolution and nucleosynthesis-Nuclear burnings take place in the stellar interiors during the star lifetime and produce new chemical elements, in particular metals.