The DLAs contribution to the metal content of the high z Universe

We investigate the evolutionary history of the Universe's metal content focusing on the chemical abundance of several elements (N, O, S, Si, Fe, Cr, Zn) taken from observational data and predictions from chemical evolution models. The estimated abundances were observed in Damped Lyman alpha Systems (DLAs) over a wide range of redshift (z ~ 0.5-4.5). These data are compared to predictions of chemical evolution models. Since the nature of the DLAs is uncertain, they are represented by two class of models: models with galactic winds describing dwarf galaxies and with infall representing disk galaxies. In order to settle constraints for star formation timescales in DLAs, we use the ratios [alpha/Fe] and [N/alpha] in the comparison to the predictions of the models. These ratios in DLAs are only partially reproduced by the disk and dwarf galaxy models suggesting that the DLAs come from a variety of morphological types of galaxies and not only one. They also imply a typically long timescale for the star formation in these systems.