We report coincident damped Lyman alpha ( DLA ) and sub-DLA absorption at z _ { abs } = 2.66 and z _ { abs } = 2.94 towards the z \sim 3 , 13.8 arcsecond separation binary quasar SDSS 1116+4118 AB .
At the redshifts of the absorbers , this angular separation corresponds to a proper transverse separation of \sim 110 h _ { 70 } ^ { -1 } kpc .
A third absorber , a sub-DLA at z _ { abs } = 2.47 , is detected towards SDSS 1116+4118 B , but no corresponding high column density absorber is present towards SDSS 1116+4118 A .
We use high resolution galaxy simulations and a clustering analysis to interpret the coincident absorption and its implications for galaxy structure at z \sim 3 .
We conclude that the common absorption in the two lines of sight is unlikely to arise from a single galaxy , or a galaxy plus satellite system , and is more feasibly explained by a group of two or more galaxies with separations \sim 100 kpc .
The impact of these findings on single line of sight observations is also discussed ; we show that abundances of DLAs may be affected by up to a few tenths of a dex by line of sight DLA blending .
From a Keck ESI spectrum of the two quasars , we measure metal column densities for all five absorbers and determine abundances for the three absorbers with log N ( HI ) > 20 .
For the two highest N ( HI ) absorbers , we determine high levels of metal enrichment , corresponding to 1/3 and 1/5 Z _ { \odot } .
These metallicities are amongst the highest measured for DLAs at any redshift and are consistent with values measured in Lyman break galaxies at 2 < z < 3 .
For the DLA at z _ { abs } = 2.94 we also infer an approximately solar ratio of \alpha -to-Fe peak elements from [ S/Zn ] = +0.05 , and measure an upper limit for the molecular fraction in this particular line of sight of log f ( H _ { 2 } ) < -5.5 .