Chemical Evolution of Galaxies in a Lambda CDM Universe

One of the fundamental questions now in Astronomy is how galaxies form and evolve. For the past years, astronomers have perfected a working paradigm for structure formation in the Universe, that of hierarchical assembly of galaxies. In this paradigm large galaxies like our own form through accretion and disruption of smaller fragments, also known as satellite galaxies. The theory of hierarchical formation has proven to be successful in explaining a variety of observational data, such as the cosmic microwave background measurements, distant supernova observations, and clustering properties of galaxies. However, most of the successes of this theory were scored through comparisons with the large scale properties of the Universe. The theory is yet to be fully validated through comparisons with ``small'' scale properties, those of the order of a typical galaxy size or less. One of the tests we can use is to explore the spatial distribution of chemical elements, such as Fe, O, Mg, etc - elements produced in supernova explonsions, in quantities determined by the star formation rate and merger history of each satellite galaxy. The present day distribution of the chemical elements holds important clues about the process of galaxy assembly. By ``chemically tagging'' present day stars, one can assign them to their progenitor satellites and therefore reconstruct the the process of Galaxy formation. Although this is an important test for the hierarchical model, it has been so far overlooked by theorists. One of the reasons for this was the scarcity of observational chemical data needed for comparisons with the theoretical model. The other was related to the inability of numerical methods to treat accurately the chemical enrichment of galaxies. Both these problems have been, or are about to be, solved. In the next few years a wealth of stellar chemical abundance data will become available from the planned kinematic and multi-object spectroscopic surveys (for example, GAIA, SEGUE or RAVE). In the same time, innovative techniques such as combining high resolution N-body simulations with semi-analytical methods have been developed and used to study the detailed spatial distribution of chemical abundances in galaxies. For the past few years I have been involved in the development of these methods and I have used them to explain a series of observations, such as the observed chemical abundance patterns in the Milky Way halo and its satellite galaxies. My proposed research is two-fold: 1) I will improve existing numerical methods for modeling the chemical evolution of galaxies; and apply them to study a large sample of model galaxies. This will give us an idea about how ``typical'' is our own Galaxy in comparison with other present day galaxies - a question that has preoccupied astronomers for a long time. 2) I will provide testable theoretical predictions for comparisons with the upcoming observational data. Large observational surveys such as GAIA, RAVE or SEGUE will soon provide kinematic and chemical abundance data for millions of stars in the Galaxy. This is a tremendous achievement in the observational techniques, made possible only by a concerted effort from the part of the astronomical community. To make the most of the large volume of upcoming observational data, one needs to have theoretical models to compare the observations against. Models of galaxy formation in the context of the hierarchical cosmology such as the ones proposed in this study will be able to provide the essential framework for understanding the observations.