The sightline to the brighter member of the gravitationally lensed quasar pair UM 673A , B intersects a damped Ly \alpha system ( DLA ) at z = 1.62650 which , because of its low redshift , has not been recognised before .
Our high quality echelle spectra of the pair , obtained with HIRES on the Keck i telescope , show a drop in neutral hydrogen column density N ( H i ) by a factor of at least 400 between UM 673A and B , indicating that the DLA ’ s extent in this direction is much less than the 2.7 h _ { 70 } ^ { -1 } kpc separation between the two sightlines at z = 1.62650 .
By reassessing this new case together with published data on other quasar pairs , we conclude that the typical size ( radius ) of DLAs at these redshifts is R \simeq ( 5 \pm 3 ) h _ { 70 } ^ { -1 } kpc , smaller than previously realised .
Highly ionized gas associated with the DLA is more extended , as we find only small differences in the C iv absorption profiles between the two sightlines .

Coincident with UM 673B , we detect a weak and narrow Ly \alpha emission line which we attribute to star formation activity at a rate { SFR } \lower 2.15 pt \hbox { $ \buildrel > \over { \sim } $ } 0.2 M _ { \odot } yr ^ { -1 } .
The DLA in UM 673A is metal-poor , with an overall metallicity Z _ { DLA } \simeq 1 / 30 Z _ { \odot } , and has a very low internal velocity dispersion .
It exhibits some apparent peculiarities in its detailed chemical composition , with the elements Ti , Ni , and Zn being deficient relative to Fe by factors of 2–3 .
The [ Zn/Fe ] ratio is lower than those measured in any other DLA or Galactic halo star , presumably reflecting somewhat unusual previous enrichment by stellar nucleosynthesis .
We discuss the implications of these results for the nature of the galaxy hosting the DLA .