We present a spectroscopic study of six damped { Ly } \alpha absorption ( DLA ) systems at z < 0.65 , based on moderate-to-high resolution spectra of the galaxies responsible for the absorbers .
Combining known metallicity measurements of the absorbers with known optical properties of the absorbing galaxies , we confirm that the low metal content of the DLA population can arise naturally as a combination of gas cross-section selection and metallicity gradients commonly observed in local disk galaxies .
We also study the Tully-Fisher relation of the DLA-selected galaxies and find little detectable evidence for evolution in the disk population between z = 0 and z \sim 0.5 .
Additional results of our analysis are as follows .
( 1 ) The DLA galaxies exhibit a range of spectral properties , from post-starburst , to normal disks , and to starburst systems , supporting the idea that DLA galaxies are drawn from the typical field population .
( 2 ) Large rotating H I disks of radius 30 h ^ { -1 } kpc and of dynamic mass M _ { dyn } > 10 ^ { 11 } h ^ { -1 } { M } _ { \odot } appear to be common at intermediate redshifts .
( 3 ) Using an ensemble of six galaxy-DLA pairs , we derive an abundance profile that is characterized by a radial gradient of -0.041 \pm 0.012 dex per kiloparsec ( or equivalently a scale length of 10.6 h ^ { -1 } kpc ) from galactic center to 30 h ^ { -1 } kpc radius .
( 4 ) Adopting known N ( \mbox { H I } ) profiles of nearby galaxies and the best-fit radial gradient , we further derive an N ( \mbox { H I } ) -weighted mean metallicity \langle Z \rangle _ { weighted } = -0.50 \pm 0.07 for the DLA population over 100 random lines of sight , consistent with \langle Z \rangle _ { weighted } = -0.64 _ { -0.86 } ^ { +0.40 } observed for z \sim 1 DLA systems from Prochaska et al .
Our analysis demonstrates that the low metal content of DLA systems does not rule out the possibility that the DLA population trace the field galaxy population .