2016MNRAS.463.2690D

In this work, we investigate the abundance and distribution of metals in the intergalactic medium (IGM) at <z> ≃ 2.8 through the analysis of an ultra-high signal-to-noise ratio UVES spectrum of the quasar HE0940-1050. In the C IV forest, our deep spectrum is sensitive at 3σ to lines with column density down to log N_CIV ≃ 11.4 and in 60 per cent of the considered redshift range down to ≃11.1. In our sample, all H I lines with log N_HI >= 14.8 show an associated C IV absorption. In the range 14.0 <= log N_HI < 14.8, 43 per cent of H I lines has an associated C IV absorption. At log N_HI < 14.0, the detection rates drop to <10 per cent, possibly due to our sensitivity limits and not to an actual variation of the gas abundance properties. In the range log N_HI >= 14, we observe a fraction of H I lines with detected C IV a factor of 2 larger than the fraction of H I lines lying in the circumgalactic medium (CGM) of relatively bright Lyman-break galaxies hosted by dark matter haloes with <M> ∼ 10¹² M_☉. The comparison of our results with the output of a grid of photoionization models and of two cosmological simulations implies that the volume filling factor of the IGM gas enriched to a metallicity logZ/Z_☉_ -3 should be of the order of ∼10-13 per cent. In conclusion, our results favour a scenario in which metals are found also outside the CGM of bright star-forming galaxies, possibly due to pollution by lower mass objects and/or to an early enrichment by the first sources.