Using spectroscopic data from the Deep Extragalactic Evolutionary Probe ( DEEP ) Groth Strip survey ( DGSS ) , we analyze the gas-phase oxygen abundances in the warm ionized medium for 64 emission-line field galaxies in the redshift range 0.26 < z < 0.82 .
These galaxies comprise a small subset selected from among 693 objects in the DGSS .
They are chosen for chemical analysis by virtue of having the strongest emission lines .
Oxygen abundances relative to hydrogen range between 8.4 < 12 + log ( O / H ) < 9.0 
with typical internal plus systematic measurement uncertainties of 0.17 dex .
The 64 DGSS galaxies collectively exhibit an increase in metallicity with B-band luminosity , i.e. , an L-Z relation like that seen among local galaxies .
Using the DGSS sample and local galaxy samples for comparison , we searched for a “ second parameter ” which might explain some of the dispersion seen in the L-Z relation .
Parameters such as galaxy color , emission line equivalent width , and effective radius were explored but found to be uncorrelated with residuals from the the mean L-Z relation .

Subsets of DGSS galaxies binned by redshift also exhibit L-Z correlations with slopes and zero-points that evolve smoothly with redshift .
DGSS galaxies in the highest redshift bin ( z = 0.6 - 0.82 ) are brighter , on average , by \sim 1 mag at fixed metallicity compared to the lowest DGSS redshift bin ( z = 0.26 - 0.40 ) and brighter by up to \sim 2.4 mag compared to local ( z < 0.1 ) emission-line field galaxies .
Alternatively , DGSS galaxies in the highest redshift bin ( z = 0.6 - 0.82 ) are , on average , 40 % ( 0.15 dex ) more metal-poor at fixed luminosity compared to local ( z < 0.1 ) emission-line field galaxies .
For 0.6 < z < 0.8 galaxies , the offset from the local L-Z relation is greatest for objects at the low-luminosity ( M _ { B } > -19 ) end of the sample and vanishingly small for objects at the high-luminosity end of the sample ( M _ { B } \sim - 22 ) .
We compare these data to simple single-zone exponential-infall Pégase2 models which follow the chemical and luminous evolution of galaxies from formation to z = 0 .
A narrow range of model parameters can qualitatively produce the slope of the L-Z relation and the observed evolution of slope and zero-point with redshift when at least two of the following are true : 1 ) low-mass galaxies have lower effective chemical yields than massive galaxies , 2 ) low-mass galaxies assemble on longer timescales than massive galaxies , 3 ) low-mass galaxies began the assembly process at a later epoch than massive galaxies .
The single-zone models do a reasonable job of reproducing the observed evolution for the low-luminosity galaxies ( M _ { B } \sim - 19 ) in our sample , but fail to predict the relative lack of evolution in the L-Z plane observed for the most luminous galaxies ( M _ { B } \sim - 22 ) .
More realistic multi-zone models will be required to explain the chemo-luminous evolution of large galaxies .