We derive oxygen abundances for a sample of 40 luminous ( M _ { B } \la - 19 ) , star-forming , mostly disk , field galaxies with redshifts in the range 0.2 \la z \la 0.8 , with a median of \left < z \right > = 0.45 .
Oxygen abundances , relative to hydrogen , of the interstellar emitting gas are estimated by means of the empirically calibrated strong emission line ratio technique .
The derived { 12 + \log ( O / H ) } values range from 8.4 to 9.0 , with a median of 8.7 .
Twenty of these galaxies have securely measured rotation velocities , in the range 50–244 kms ^ { -1 } .

The measured emission line equivalent widths and diagnostic ratios for the intermediate redshift galaxies cover similar ranges to those observed across a large sample of local galaxies .
The estimated oxygen abundances for our luminous star-forming intermediate redshift galaxies cover the same range as their local counterparts .
However , at a given galaxy luminosity , many of our galaxies have significantly lower oxygen abundances , i.e. , { \mbox { $ { 12 + \log ( O / H ) } $ } } \sim 8.6 , than local galaxies with similar luminosities .
Interestingly , these luminous , massive , intermediate redshift , star-forming galaxies with low oxygen abundances exhibit physical conditions , i.e. , emission line equivalent width and ionization state , very similar to those of local faint and metal-poor star-forming galaxies .
The oxygen abundance of the interstellar gas does not seem to correlate with the maximum rotation velocity or the emission scale length of the parent galaxy .
This suggests that there is a diversity in the intrinsic properties of the massive field galaxy population at intermediate redshifts

The distribution of the colour excess , derived from the ratio of extinction-uncorrected { H \beta } and { [ OII ] \lambda 3727 } star formation rate indicators , covers a similar range to that observed locally , but exhibits a lower mean than is observed for local optically-selected star-forming galaxies .
Luminous field galaxies at intermediate redshifts show similar star formation rates to their local counterparts .
However , metal-poor , massive , star-forming galaxies tend to be systematically less affected by internal reddening than metal-rich , massive galaxies , which cover similar range of colour excess to local metal-rich luminous galaxies .
Finally , the correlation between oxygen abundance and colour excess for intermediate redshift galaxies is found to be similar to what is observed locally .
This result indicates that the dust content of galaxies is more regulated by their chemical evolution rather than galaxy luminosity .