We present the chemical abundance measurements of the first large , medium-resolution , uniformly selected damped Lyman- \alpha system ( DLA ) survey .
The sample contains 99 DLAs towards 89 quasars selected from the SDSS DR5 DLA sample in a uniform way .
We analyze the metallicities and kinematic diagnostics , including the velocity width of 90 % of the optical depth , \Delta v _ { 90 } , and the equivalent widths of the Si ii \lambda 1526 ( W _ { \lambda 1526 } ) , C iv \lambda 1548 and Mg ii \lambda 2796 transitions .
To avoid strong line-saturation effects on the metallicities measured in medium-resolution spectra ( FWHM \sim 71 km s ^ { -1 } ) , we derived metallicities from metal transitions which absorbed at most 35 % of the quasar continuum flux .
We find the evolution in cosmic mean metallicity of the sample , \langle Z \rangle = ( - 0.04 \pm 0.13 ) z - ( 1.06 \pm 0.36 ) , consistent with no evolution over the redshift range z \sim [ 2.2 , 4.4 ] , but note that the majority of our sample falls at z \sim [ 2.2 , 3.5 ] .
The apparent lack of metallicity evolution with redshift is also seen in a lack of evolution in the median \Delta v _ { 90 } and W _ { \lambda 1526 } values .
While this result may seem to conflict with other large surveys that have detected significant metallicity evolution , such as ( ) who found \langle Z \rangle = ( - 0.22 \pm 0.03 ) z - ( 0.65 \pm 0.09 ) over z \sim [ 0 , 5 ] , several tests show that these surveys are not inconsistent with our new result .
However , over the smaller redshift range covered by our uniformly-selected sample , the true evolution of the cosmic mean metallicity in DLAs may be somewhat flatter than the ( ) estimate .