Understanding the correlations between abundances and column density in Damped Lyman Alpha systems

Damped Lyman Alpha systems are high Hydrogen column density gaseous systems (N(HI)>2.10^20 cm-²) detected through their absorption lines in the optical spectra of quasars (QSO-DLAs) up to redshift z=6. The term Damped Lyman Alpha refers to the Lyman alpha line of the neutral hydrogen which is observed to be saturated. DLAs are said to be the progenitors of the present day galaxies, so their study is an important tool for understanding the structure of young galactic systems. A large collect of elemental abundances has been made from the most recent articles. Moreover, in order to extend the study to different types of Damped systems the analysis has not been restricted to QSO-DLAs only, but sub-DLAs and GRB-DLAs (Gamma Ray Bursts-DLAs) have been added. The aim is to acquire information on a large number of Damped systems so as to get a general overview of their chemical structure. A first observation has been made on the different metallicities and HI columns density of these systems. An anti-correlation between metallicity and HI column density has been noticed. By rejecting the idea that the observations are biased, this anti-correlation has been considered to be real. A main property of these systems is the depletion of some elements in dust grains. The result is that the observed abundances do not account for the real value. Indeed the part of the elements which is locked onto the dust grains is not detectable by the telescopes. A study of the different correlations between abundances and abundances ratios has been made, and then compared to abundances in other galaxies, like the Milky Way. We could indeed point out the presence of dust depletion in DLAs. Another important concept about the chemical structure of these systems is their chemical enrichment during their evolution. The nucleosynthesis processes are different from one element to another, the abundances depend on the age of the universe. The alpha elements (Si, S,..) are mainly synthesized during supernovae type II which occur early in the universe history, whereas the Fe elements are mainly produced during supernovae type Ia which occur later. However, the nucleosynthesis of zinc is not well known. According to the different correlation observed, Zn seems to be produced by both type of supernovae (II and Ia). An analysis on the abundances of more systems would be helpful to confirm or deny this observation. In order to describe the chemical evolution of the systems, a model has been developed with MATLAB based on 25 models of spiral disks galaxies (Boissier & Prantzos 2000,1999). We have noticed that the model would benefit from extending to other galaxy types. Since it accounts for spiral disk galaxies only, the other galaxies types are not represented. To better match the observed abundances evolution of DLAs, we have suggested adding the abundances evolution of galaxies types such as irregulars and dwarf elliptical galaxies from the local neighborhood of the Milky Way.Validerat; 20101217 (root