Quasars absorption-line system

Observations of distant objects, notably high-redshift star-forming ( Lyman-break ) galaxies and absorption line systems on the line of sight to quasars, give some information on chemical evolution at epochs not too far from when the first stars and most galaxies were presumably formed. Other information comes from two related effects ... 

This work has been continued in Ref. [3]. A large set of data consists of 49 quasar absorption systems located between 4 and 11 billion light years from us (starting from 10% of the age of the Universe after Big Bang). Many lines of Mgl, Mgll, Alii, Aim, Sill, Crll, Fell, Nill and Znll have been included and a study of both temporal and spatial dependence of a has been performed. For the whole sample, Aa/a = (—7.5 1.8) x 10 6. We should stress that only statistical errors are presented here. This error is now small and the main efforts are directed towards the study of various systematic effects [20]. 

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