Integral field spectroscopy with SINFONI of VVDS galaxies^*

II. The mass–metallicity relation at 1.2 < z < 1.6

¹ Laboratoire d'Astrophysique de Toulouse-Tarbes, Université de Toulouse, CNRS, 14 Avenue Édouard Belin, 31400 Toulouse, France e-mail: jqueyrel@ast.obs-mip.fr
² Instituto de Astrofísica de Andalucía – CSIC Apdo. 3004 18080 Granada, Spain
³ IASF-INAF, Via Bassini 15, 20133 Milano, Italy
⁴ Laboratoire d'Astrophysique de Marseille, Université de Provence, CNRS, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France
⁵ ESO, Karl-Schwarzschild-Str.2, 85748 Garching b. München, Germany
⁶ INAF - Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁷ Oxford Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK

Received: 6 March 2009
Accepted: 7 August 2009

Abstract

Aims. This work aims to provide a first insight into the mass–metallicity (MZ) relation of star-forming galaxies at redshift z ~ 1.4. To reach this goal, we present a first set of nine VVDS (VIMOS VLT Deep Survey) galaxies observed with the NIR integral-field spectrograph SINFONI on the VLT.

Methods. Oxygen abundances are derived from empirical indicators based on the ratio between strong nebular emission-lines (Hα, [N ii]6584 Å and [S ii]6717, 6731 Å). Stellar masses are deduced from SED fitting with Charlot & Bruzual (2003) population synthesis models, and star formation rates are derived from [O ii]3727 Å and Hα emission-line luminosities.

Results. We find a typical shift of  dex towards lower metallicities for the z ~ 1.4 galaxies, compared to the MZ-relation in the local universe as derived from SDSS data. However, this small sample does not show any clear correlation between stellar mass and metallicity, unlike other larger samples at different redshift (z ~ 0, z ~ 0.7, and z ~ 2). Indeed, our galaxies lie just under the relation at z ~ 2, and show a small trend for more massive galaxies to be more metallic (~0.1 logarithmic slope). There are two possible explanations to account for these observations. First, our galaxies present higher specific star formation rates when compared to the global VVDS sample which could explain the particularly low metallicity of these galaxies as already shown in the SDSS sample. Second, inflow of metal-poor gas due to tidal interactions could also explain the low metallicity of these galaxies as three of these nine galaxies show clear signatures of merging in their velocity fields. Finally, we find that the metallicity of four galaxies is lower by ~0.2 to 0.4 dex if we take into account the N/O abundance ratio in their metallicity estimate.