A deep search for metals near redshift 7: the line-of-sight towards ULAS J1120+0641

Understand

We present a search for metal absorption line systems at the highest redshifts to date using a deep (30h) VLT/X-Shooter spectrum of the z = 7.084 quasi-stellar object (QSO) ULAS J1120+0641.

• We detect seven intervening systems at z > 5.5, with the highest-redshift system being a C IV absorber at z = 6.51.
• We find tentative evidence that the mass density of C IV remains flat or declines with redshift at z < 6, while the number density of C II systems remains relatively flat over 5 < z < 7.
• These trends are broadly consistent with models of chemical enrichment by star formation-driven winds that include a softening of the ultraviolet background towards higher redshifts.