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H. Kobulnicky, C.N.A. Willmer, B.J. Weiner, D.C. Koo, A.C Phillips, S.M. Faber (UC Santa Cruz), V.L. Sarajedini (University of Florida), L. Simard (Dominion Astrophysical Observatory), N.P. Vogt (New Mexico State University)
Using spectroscopic data from the DEEP Groth Strip Survey (DGSS), we analyze the gas-phase oxygen abundances for 66 field galaxies in the redshift range z=0.26-0.82. We develop a prescription for estimating the nebular oxygen abundance of distant galaxies using the equivalent width of strong [O~II], [O~III], and Balmer emission lines. Oxygen abundances for the DGSS sample, relative to hydrogen, range between 8.4<12+log(O/H)<9.0 with typical uncertainties of 0.10 dex. The 66 DGSS galaxies collectively exhibit a correlation between B-band luminosity and metallicity. Subsets of DGSS galaxies binned by redshift also exhibit correlations but with different zero points. Galaxies in the highest redshift bin (z=0.6-0.82) are brighter by ~ mag compared to the lowest redshift bin (z=0.6-0.82) and brighter by ~-2 mag compared to local (z<0.1) field galaxies. This offset from the local L-Z relation for field galaxies is greatest for objects at the low-luminosity (MB~19) end of the sample, and vanishingly small for objects at the high-luminosity end of the sample (MB~22). This result implies that emission-line field galaxies have undergone moderate amounts of evolution in the past ~ Gyr since z~.8, and that the evolution is most significant for galaxies of lower luminosity. Either the least-luminous DGSS field galaxies have faded by 1--2 mag due to decreasing levels of star formation, or they have experienced an increase in the mean metallicity of the interstellar medium by factors of 1.3--2 (0.1-0.3 dex). Some combination of the two processes is likely.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.