SIMBAD references

We present the first theoretical study of metals in damped-Lyα (DLA) systems at redshift z ≃ 7. The features of cold, primordial gas are studied by means of N-body, hydro, chemistry simulations, including atomic and molecular non-equilibrium chemistry, cooling, star formation for Population III and Population II-I regimes, stellar evolution, cosmic metal spreading according to proper yields (for He, C, O, Si, Fe, Mg, S, etc.) and lifetimes and feedback effects. Theoretical expectations are then compared to recently available constraints from DLA observations.

We find that DLA galaxies at z ≃ 7 account for ∼ 10 percent of the whole galaxy population and for most of the metal-poor galaxies at these epochs. About 7 percent of these DLA galaxies contain purely pristine material and ∼ 34 percent of them consist of very weakly polluted gas, being, therefore, suitable candidates as Population III sites. The remaining ∼ 59 percent are enriched above ∼ 10^–4Z_☉. Additionally, DLA candidates appear to have: gas masses ≲ 2x10⁸M_☉; very low star formation rate, ∼ 10^- 3^–10- 2^M_☉/yr (significantly weaker than late-time counterparts); mean molecular fractions covering a fairly wide range, xmol ∼ 10^- 3^–10- 6^; typical metallicities Z ≲ 10^–3Z_☉ and Hi column densities N_H I\gtrsim 3×10^20  cm^-2 (in agreement with recent observations). They present no or weak correlations between their gas mass and Z, N_H I, or xmol; a moderate correlation between xmol and Z, linked to the ongoing molecular-driven star formation and metal pollution processes; a mild anticorrelation between N_H I and xmol, due to H depletion into molecules; and a chemical content that is subject to environmental dependences.