Physical properties of galaxies and their evolution in the VIMOS VLT Deep Survey I. The evolution of the mass-metallicity relation up to z ∼ 0.9

Aims. We want to derive the mass-metallicity relation of star-forming galaxies up to z similar to 0.9, using data from the VIMOS VLT Deep Survey. The mass-metallicity relation is commonly understood as the relation between the stellar mass and the gas-phase oxygen abundance. Methods. Automatic measurement of emission-line fluxes and equivalent widths have been performed on the full spectroscopic sample of the VIMOS VLT Deep Survey. This sample is divided into two sub-samples depending on the apparent magnitude selection: wide (I(AB) < 22.5) and deep (I(AB) < 24). These two samples span two different ranges of stellar masses. Emission-line galaxies have been separated into star-forming galaxies and active galactic nuclei using emission line ratios. For the star-forming galaxies the emission line ratios have also been used to estimate gas-phase oxygen abundance, using empirical calibrations renormalized in order to give consistent results at low and high redshifts. The stellar masses have been estimated by fitting the whole spectral energy distributions with a set of stellar population synthesis models. Results. We assume at first order that the shape of the mass-metallicity relation remains constant with redshift. Then we find a stronger metallicity evolution in the wide sample as compared to the deep sample. We thus conclude that the mass-metallicity relation is flatter at higher redshift. At z similar to 0.77, galaxies at 10(9.4) solar masses have -0.18 dex lower metallicities than galaxies of similar masses in the local universe, while galaxies at 10(10.2) solar masses have -0.28 dex lower metallicities. By comparing the mass-metallicity and luminosity-metallicity relations, we also find an evolution in mass-to-light ratio: galaxies at higher redshifts being more active. The observed flattening of the mass-metallicity relation at high redshift is analyzed as evidence in favor of the open-closed model.