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

作者：Bosman Sarah E I; Becker George D; Haehnelt Martin G; Hewett Paul C; McMahon Richard G; Mortlock Daniel J; Simpson Chris; Venemans Bram P

来源：Monthly Notices of the Royal Astronomical Society, 2017, 470(2): 1919-1934.

DOI：10.1093/mnras/stx1305

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

We present a search for metal absorption line systems at the highest redshifts to date using a deep (30 h) Very Large Telescope/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 < 0.3 angstrom) 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 less than or similar to 2.5, and suggests that the mechanisms that create these absorbers are already in place at z similar to 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.

• 出版日期2017-9