The Metallicity of Redshift 0.5<z<1 Field Galaxies

We are undertaking a program to measure emission line ratios in a selected sample of $0.5<z<1.0$ CFRS starforming galaxies in order to compute their Interstellar Medium metallicities. The latter are derived by means of the empirically-calibrated $R_{23}$ estimator introduced by Pagel et al. (1979). Here we focus on a subsample of 15 galaxies with $L_{H\beta} > 1.2 \times 10^{41}$ergs$^{-1}$. In addition to the optical CFHT spectra discussed in Carollo & Lilly (2001), where a preliminary account of this work can be found, in this paper we also refer to new $J$-band Keck spectroscopy of the $H\alpha$ and [NII]6583 lines for several objects. These lines allow us to break the degeneracy between low ($\text{lta}0.1Z_{\odot }$) and high ($\text{gta}0.5Z_{\odot }$) metallicity of the $R_{23}$ estimator, and put on solid ground the finding that the $0.5<z<1.0$ blue galaxies in the high-$L_{H\beta }$ sample are significantly metal-enriched ($Z\text{gta}0.3Z_{\odot }$ up to $Z_{\odot }$). Therefore, our results do not support previous suggestions in which the $0.5<z<1.0$ starforming galaxies are dwarf galaxies brightened by large bursts of star-formation, but support instead a picture where at least a significant fraction of them evolves to become today’s massive metal-rich systems.