http://arxiv.org/abs/1705.08925
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.
S. Bosman, G. Becker, M. Haehnelt, et. al.
Fri, 26 May 17
-2/63
Comments: 18 pages, 23 figures, accepted for publication in MNRAS