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

Abstract

In this work, we investigate the abundance and distribution of metals in the intergalactic medium (IGM) at $\langle z \rangle \simeq 2.8$ through the analysis of an ultra-high signal-to-noise ratio UVES spectrum of the quasar HE0940-1050. In the CIV forest, our deep spectrum is sensitive at $3\,\sigma$ to lines with column density down to $\log N_{\rm CIV} \simeq 11.4$ and in 60 per cent of the considered redshift range down to $\simeq11.1$. In our sample, all HI lines with $\log N_{\rm HI} \ge 14.8$ show an associated CIV absorption. In the range $14.0 \le \log N_{\rm HI} <14.8$, 43 per cent of HI lines has an associated CIV absorption. At $\log N_{\rm HI} < 14.0$, 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 $\log N_{\rm HI} \ge 14$, we observe a fraction of HI lines with detected CIV a factor of 2 larger than the fraction of HI lines lying in the circum-galactic medium (CGM) of relatively bright Lyman-break galaxies hosted by dark matter haloes with $\langle M\rangle \sim10^{12}$ M$_{\odot}$. 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 $\log Z/Z_{\odot} \ge -3$ should be of the order of $\sim 10-13$ percent. 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.MV is supported by the ERC Starting Grant ‘cosmoIGM’ and PD51 INDARK grant. TSK acknowledges funding support from the ERC Starting Grant ‘cosmoIGM’, through grant GA-257670. MH was supported by the ERC Advanced Grant 320596 ‘The Emergence of Structure during the epoch of Reionisation’. PB is supported by the INAF PRIN-2014 grant ‘Windy black holes combing galaxy evolution’. Parts of this research were conducted by the Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO), through project number CE110001020.This is the final version of the article. It first appeared from Oxford University Press via http://dx.doi.org/10.1093/mnras/stw216