Simulating cosmic metal enrichment by the first galaxies

We study cosmic metal enrichment via adaptive mesh refinement hydrodynamical simulations in a (10 Mpc h(-1))(3) volume following the Population III (PopIII)-PopII transition and for different PopIII initial mass function (IMFs). We have analysed the joint evolution of metal enrichment on galactic and intergalactic scales at z = 6 and z = 4. Galaxies account for less than or similar to 9 per cent of the baryonic mass; the remaining gas resides in the diffuse phases: (a) voids, i.e. regions with extremely low density (delta < 1), (b) the true intergalactic medium (IGM, 1 < delta < 10) and (c) the circumgalactic medium (CGM, 10 < delta < 10(2.5)), the interface between the IGM and galaxies. At z = 6, a galactic mass-metallicity relation is established. At z = 4, galaxies with a stellar mass M-* similar or equal to 10(8.5) M-circle dot show log(O/H) + 12 = 8.19, consistent with observations. The total amount of heavy elements rises from Omega(SFHz)(Z) 1.52 x 10(-6) at z = 6 to 8.05 x 10(-6) at z = 4. Metals in galaxies make up to similar or equal to 0.89 of such budget at z = 6; this fraction increases to similar or equal to 0.95 at z = 4. At z = 6 (z = 4), the remaining metals are distributed in CGM/IGM/voids with the following mass fractions: 0.06/0.04/0.01 (0.03/0.02/0.01). Analogously to galaxies, at z = 4 a density-metallicity (Delta - z) relation is in place for the diffuse phases: the IGM/voids have a spatially uniform metallicity, Z similar to 10(-3.5) Z(circle dot); in the CGM, Z steeply rises with density up to similar or equal to 10(-2) Z(circle dot). In all diffuse phases, a considerable fraction of metals is in a warm/hot (T mu(-1) > 10(4.5) K) state. Due to these physical conditions, C IV absorption line experiments can probe only similar or equal to 2 per cent of the total carbon present in the IGM/CGM; however, metal absorption line spectra are very effective tools to study reionization. Finally, the PopIII star formation history is almost insensitive to the chosen PopIII IMF. PopIII stars are preferentially formed in truly pristine (Z = 0) gas pockets, well outside polluted regions created by previous star formation episodes.