J1047+2057: Both Ca II H&K and Na I D are detected and strong. The spectrum around Na I D is noisy however, thus the error on EW is relatively large. The redshift defined by the strongest C I component does not correspond to the exact centre of the Na I D lines. The strongest component of Na I D is shifted by around 25 km s−1 compared to C I. This may be an artefact of the intermediate resolution of X-shooter as the C I fit is complex and needs at least three components. Higher resolution data are needed to study in more detail the structure of the absorbing cloud. The elements H2 and CO are detected. Mg II for this system is uncommonly strong and spans around 800 km s−1 including components at −350 km s−1 and +400 km s−1. Noterdaeme et al. (2010a) first detected CO in this system and used it to measure the cosmic microwave background (CMB) temperature at the corresponding redshift. They obtain a column density of log N(CO) = 14.74 ± 0.07. From the X-shooter data we derive log N(CO) = 14.56 ± 0.92, which is in agreement with the result by Noterdaeme et al. (2011). Daprà et al. (2016) used the CO absorption from this system to constrain the cosmological variation of the proto-to-electron mass ratio. NiII and ZnII are detected.
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