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Centro de Astrofísica da Universidade do Porto

Spectrophotometric properties of galaxies at intermediate redshifts (z ~ 0.2-1.0). II. The Luminosity - Metallicity relation

F. Lamareille, T. Contini, J. Brinchmann, J.-F. Le Borgne, S. Charlot, J. Richard

We present the gas-phase oxygen abundance (O/H) for a sample of 131 star-forming galaxies at intermediate redshifts (0.2<z<1.0). The sample selection, the spectroscopic observations (mainly with VLT/FORS) and associated data reduction, the photometric properties, the emission-line measurements, and the spectral classification are fully described in a companion paper (Paper I). We use two methods to estimate the O/H abundance ratio: the "standard" R23 method which is based on empirical calibrations, and the CL01 method which is based on grids of photo-ionization models and on the fitting of emission lines. For most galaxies, we have been able to solve the problem of the metallicity degeneracy between the high- and low-metallicity branches of the O/H vs. R23 relationship using various secondary indicators. The luminosity - metallicity (L-Z) relation has been derived in the B- and R-bands, with metallicities derived with the two methods (R23 and CL01). In the analysis, we first consider our sample alone and then a larger one which includes other samples of intermediate-redshift galaxies drawn from the literature. The derived L-Z relations at intermediate redshifts are very similar (same slope) to the L-Z relation obtained for the local universe. Our sample alone only shows a small, not significant, evolution of the L-Z relation with redshift up to z∼1.0. We only find statistical variations consistent with the uncertainty in the derived parameters. Including other samples of intermediate-redshift galaxies, we find however that galaxies at z∼1 appear to be metal-deficient by a factor of ∼3 compared with galaxies in the local universe. For a given luminosity, they contain on average about one third of the metals locked in local galaxies.

Astronomy and Astrophysics
Volume 448, Page 907
March 2006

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