We have recently completed the measurement of the abundances of the elements Zn and Cr in a small, but complete, sample of damped Lyman alpha systems selected irrespectively of their dust content (the CORALS radio sample). We find that at a mean redshift z = 2.4 their metallicity and degree of dust depletion are statistically indistinguishable from those of larger samples of DLAs assembled from optical surveys. Thus we conclude that reasons other than a dust-induced bias must be found to explain the lack of redshift evolution in the metallicity of the galaxies giving rise to DLAs, and their generally low degree of chemical enrichment compared with luminous galaxies observed at the same epoch.

The question of how metals are produced in the Universe and where they are located is fundamental for our understanding of galaxy formation and evolution. This question can be best addressed using absorption lines seen in the spectra of remote quasars. It has been realized that the spatial distribution of metals around galaxies and more generally in the Intergalactic Medium is complex, and it is often very difficult to associate one absorption system with one galaxy. Except for possibly in the special case of DLA systems, it may be more appropriate to discuss the clustering properties of different classes of objects and to measure their correlation functions. I illustrate these issues with three examples: the distribution of metals around galaxies at intermediate redshift, the modelling of the clustering of C IV systems, and the determination of abundances in Damped Lyman-α systems (and in particular the oxygen abundance). Finally, I note that there is a mass-metallicity relation in Damped Lyman-α systems.

By means of chemical evolution models for galaxies of different morphological types (i.e. spirals and irregular/starburst galaxies) we study the nature of Damped Lyman-alpha (DLA) systems. By focusing on individual systems, we can derive important constraints on both their star formation history and their age. Our results indicate that the local conterparts of most DLAs are represented by dwarf galaxies having had low star formation rates, but some systems can also be associated to spirals. Some systems are already old, with ages of ∼1 Gyr, and some others are experiencing the very first star formation episodes.

The Fe/Mg abundance ratio may be one of the fundamental indicators for nucleosynthesis in the Early Universe. Even at the highest redshift, QSO broad-lined regions (BLRs) exhibit prominent 2000-3000Å Fe II(UV) band and Mg II 2800Å resonance doublet emission in the restframe UV. The Mg is formed in Type-II SNe, while Fe has been traditionally thought to be produced in Type Ia SNe. These different origins imply a sharp falloff in Fe abundance at very high-z. However, these predictions are clouded by uncertainties about the nature of the first stars and in the nuclear yields from supernovae models. Our theoretical studies of Fe II in QSO BLRs show that Fe and Mg abundance cannot be directly deduced from the observed Fe II(UV)/Mg II, because it is sensitive to luminosity and microturbulence, as well as abundance. Observationally, support for a luminosity dependence comes from SDSS data for QSOs that show a Fe II(UV)/Mg II correlation with luminosity at z ∼ 1.8–2.0.

We present the values of CN and Mg overabundances with respect to Fe, for a large sample of elliptical galaxies in different environments. Abundances were derived by confronting observed absorption line indices with stellar population model spectra. We obtained significant differences between the [CN/Fe] and [Mg/Fe] abundance ratios as a functions of: i) the environment, and ii) the galaxy mass. This is interpreted as implying varying formation timescales for CN, Mg and Fe, combined with different star formation histories in elliptical galaxies depending on their mass and environment. Our principal conclusions are: 1) CN is sensitive to the characteristic assembly timescales of elliptical galaxies, 2) more massive elliptical galaxies are assembled on shorter timescales than less massive ones, 3) elliptical galaxies in denser environments are assembled on shorter timescales than those in lower density environments, and 4) our results strongly suggest an upper limit for the assembly timescale of ∼1 Gy, in all cases.

Some basic observational properties of Damped Lymna α systems (DLAs) have been examined by Monte Carlo simulation based on the assumption that DLAs are disks form at the center of dark halo at redshift 3. We found that the predicted cosmic star formation rate density contributed by DLAs is consistent with the most recent observations if the star formation timescale in DLAs is assumed to be 1 ∼ 3 Gyr. By comparing the UV luminosity function between DLA host galaxies and that of Lyman Break Galaxies(LBGs), we show that the DLAs host galaxies are much fainter than LBGs, and that only few percent of DLAs can host LBGs. The discrepancy between model prediction and observation in the correlation between metallicity and HI column density for DLAs is reproduced on the basis of Kennicutt star formation formalism at high redshift. It is quite difficult to interpret this concerning the complexities of dust depletion, star formation mode as well as model limitations. Further investigations are needed.

We assume that Damped Lyman-α absorbers are gas rich galaxies on early stages of their evolution, and check this idea on the basis of a spectrophotometric, chemical and dust evolution model. Influence of the dust on the chemical pattern of galaxies is calculated self-consistently according Dwek's (1998) model, where up-to-date dust yields from supernovae, intermediate and low mass stars on their AGB phase are taken into account. We conclude that gas rich galaxies are good candidates on the role of DLA systems.

In grand design spiral galaxies, spiral arms play a dominant role in the oxygen enrichment rate, since type II supernovae are the main source of oxygen, and these supernovae only appear in spiral arms. The connection between the spiral structure and the star formation rate explains oxygen abundance gradients that rise outward, in the external regions of a number of galaxies.

HE0141-3932 ($z_{\rm em} = 1.80$) is a bright blue radio-quiet quasar which reveals an emission line spectrum with an unusually weak Lyα line. In addition, large redshift differences ($\Delta z = 0.05$) are observed between high ionization and low ionization emission lines. Absorption systems identified at $z_{\rm abs} = 1.78, 1.71$, and 1.68 show mild oversolar metallicities ($Z \approx 1-2Z_\odot$) and can be attributed to the associated gas clouds ejected from the circumnuclear region. The joint analysis of the emission and absorption lines leads to the conclusion that this quasar is seen almost pole-on. Its apparent luminosity may be Doppler boosted by ∼10 times. The absorbing gas shows high abundance of Fe, Mg, and Al ([Fe, Mg, Al/C] $\simeq 0.15\pm0.10$) along with underabundance of N ([N/C] $\leq -0.5$). This abundance pattern is at variance with current chemical evolution models of QSOs predicting [N/C] < 0 and [Fe/C] <0 at $Z \sim Z_\odot$. Full details of this work are given in Reimers et al. (2005).

Attempts are made to summarize some main points and results discussed at the IAU Symposium No. 228 in Paris, May 2005. It is concluded that, although the situation in areas pioneered by F. and M. Spite is nowdays rather complex, some important progress has recently been made, and more is expected to occur within the next few years if the level of ambition in the astronomical community is kept at the high level set by the pioneers.