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

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Bosman, SEI 
Becker, GD 
Haehnelt, MG 
Hewett, PC 
McMahon, RG 


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.



intergalactic medium, quasars: absorption lines, quasars: individual: ULAS J1120+0641, dark ages, reionization, first stars

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Monthly Notices of the Royal Astronomical Society

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Oxford University Press (OUP)
Science and Technology Facilities Council (ST/H00243X/1)
Science and Technology Facilities Council (ST/K000985/1)
Science and Technology Facilities Council (ST/N000927/1)
European Research Council (320596)
Science and Technology Facilities Council (ST/L002582/1)
STFC (1494252)