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

Abstract

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. We find a larger number of weak ( W_rest < 0.3A ) Mg II systems over 5.9 < z < 7.0 than predicted by a power-law fit to the number density of stronger systems. This is consistent with trends in the number density of weak Mg II systems at z = 2.5, and suggests that the mechanisms that create these absorbers are already in place at z = 7. Finally, we investigate the associated narrow Si IV, C IV, and N V absorbers located near the QSO redshift, and find that at least one component shows evidence of partial covering of the continuum source.

18 pages, 23 figures, accepted for publication in MNRAS

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• Metal enrichment and evolution in four z > 6.5 quasar sightlines observed with JWST/NIRSpec
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• The comoving mass density of MgII from $z\sim 2$ to $5.5$
• Aligned metal absorbers and the ultraviolet background at the end of reionization
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• Constraining IGM enrichment and metallicity with the C IV forest correlation function
• Cospatial 21 cm and metal-line absorbers in the epoch of reionization -- I : Incidence and observability
• Origin of Weak MgII and Higher Ionization Absorption Lines in an Outflow from an Intermediate-Redshift Dwarf Satellite Galaxy
• How far have metals reached? Reconciling statistical constraints and enrichment models at reionization
• The clustering of C IV and Si IV at the end of reionisation: A perspective from the E-XQR-30 survey
• Modelling intergalactic low ionisation metal absorption line systems near the epoch of reionization