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We present the first theoretical study of metals in damped Ly-alpha (DLA)systems at redshift z=7. The features of cold, primordial gas are studied bymeans of N-body, hydro, chemistry simulations, including atomic and molecularnon-equilibrium chemistry, cooling, star formation for population III andpopulation II-I regimes, stellar evolution, cosmic metal spreading according toproper yields (for He, C, O, Si, Fe, Mg, S, etc.) and lifetimes, and feedbackeffects. Theoretical expectations are then compared to recently availableconstraints from DLA observations. We find that DLA galaxies at z=7 account for10 per cent of the whole galaxy population and for most of the metal-poorgalaxies at these epochs. About 7 per cent of these DLA galaxies contain purelypristine material and 34 per cent of them consist of very weakly polluted gas,being, therefore, suitable candidate s as population III sites. The remaining59 per cent are enriched above ~10^{-4} Zsun. Additionally, DLA candidatesappear to have: gas masses <~2x10^8 Msun; very low star formation rate,~10^{-3} - 10^{-2} Msun/yr (significantly weaker than late-time counterparts);mean molecular fractions covering a fairly wide range, x_mol~10^{-3}- 10^{-6};typical metallicities Z<~3x10^{-3}Zsun and HI column densities NHI>~3x10^{20}cm^{-2}. They present no or weak correlations between their gas mass and Z,NHI, or x_mol; a moderate correlation between x_mol and Z, linked to theongoing molecular-driven star formation and metal pollution processes; a mildanti-correlation between NHI and x_mol, due to H depletion into molecules; anda chemical content that is subject to environmental dependencies.

Simulating extremely metal-poor gas and DLA metal content at redshift z=7