A galaxy as the source of a Civ absorption system close to the epoch of reionization

Abstract: We find a bright (L_{UV}=2.5 L*{z=6}) Lyman alpha emitter at redshift z=5.719 at a projected distance of 79 physical kpc from a strong triply ionized carbon (Civ) absorption system at redshift z=5.7238 previously reported in the spectrum of the z{em} = 6.309 QSO SDSS J1030+0524. This is the highest redshift galaxy-absorber pair detected to-date, supporting the idea that galaxy-wide outflows were already in place at the end of the epoch of reionization. The proximity of this object makes it the most likely source of metals, consistent with models of outflows at lower redshift where significant observational evidence relates metal absorption systems with galaxies hosting outflows. In a typical outflow scenario, a wind of 200 km/s, active since the universe was only 0.6 Gyr old (z ~8.4), could eject metals out to 79 kpc at z=5.719. Although the origin of metals in the intergalactic medium (IGM) is still under debate, our results are consistent with predictions from cosmological simulations which reproduce the evolution of the cosmic density of Civ, from z ~ 6 to the present day based on outflow-driven enrichment of the IGM. We also report two more Lyman alpha emitters in this field, at z=5.973\pm 0.002 and z=5.676\pm 0.002 respectively, the former confirming the original identification by Stiavelli et al. Our results suggest that the colour cut typically used to identify i-dropouts (i_{775}-z_{850}>1.3) misses a non-negligible fraction of blue galaxies with faint UV continuum at z \geq 5.7.