| Despite considerable progress in recent years, a complete description of the physical drivers of galaxy formation and evolution remains elusive, in part because of our poor understanding of star formation, and how star formation in galaxies is regulated by feedback from supernovae and massive stellar winds. Insight into the star formation histories of galaxies, and the interplay between star formation and feedback, can be gained by measuring their chemical abundances, which until recently has only been possible for galaxies in the nearby universe. However, reliable star formation and abundance calibrations have been hampered by various systematic uncertainties, and the lack of a suitable spectrophotometric sample with which to develop better calibrations. To address the limitations of existing surveys, we have obtained integrated optical spectra for a diverse sample of more than four hundred nearby star-forming galaxies. Using these data, in conjunction with observations from the Sloan Digital Sky Survey, we conduct a detailed analysis of optical star formation indicators, and develop empirical calibrations for the [O II] lambda3727 and Hbeta lambda4861 nebular emission lines. Next, we investigate whether integrated spectroscopy of star forming galaxies can be used to infer their gas-phase oxygen abundances in the presence of radial abundance gradients, diffuse-ionized gas emission, and dust attenuation. We conclude that the integrated R23R23 parameter is generally insensitive to these systematic effects, enabling the gas-phase metallicity to be measured with a precision of +/-0.1 dex. We apply these methods to study the evolution in the luminosity-metallicity relation at 0 < z < 1 based on an analysis of more than 3500 I-band selected galaxies observed as part of the AGN and Galaxy Evolution Survey, and data culled from the literature. Our principal results are that, at fixed luminosity, the mean gas-phase metallicity of luminous (MB < -19 mag), star-forming galaxies at z = 1 is a factor of two lower than the gas-phase metallicity in comparably luminous galaxies at z = 0. However, after accounting for the effects of luminosity evolution, we find that the amount of chemical evolution for luminous galaxies corresponds to an increase of only 10%--20% since z ≈ 1, assuming a direct evolutionary connection between nearby and distant star-forming galaxies. |
