Metals in the z ̃ 3 intergalactic medium: results from an ultra-high signal-to-noise ratio UVES quasar spectrum

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 3a to lines with column density down to log NCIV ≃ 11.4 and in 60 per cent of the considered redshift range down to ≃11.1. In our sample, all Hi lines with log NHI ≥ 14.8 show an associated C iv absorption. In the range 14.0 ≤ log NHI < 14.8, 43 per cent of Hi lines has an associated Civ absorption. At log NHI < 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 Nhi ≥ 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 Mo ̇. 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 log Z/Zo ̇ ≳ - 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. © 2016, The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.