Oxygen abundances of zCOSMOS galaxies at z~1.4 based on five lines and implications for the fundamental metallicity relation

TL;DR

This study measures gas-phase metallicities of z~1.4 galaxies using five emission lines, finding a significant evolution in the mass-metallicity relation and supporting a non-evolving fundamental metallicity relation at high redshift.

Contribution

It provides new metallicity measurements based on five lines for galaxies at z~1.4 and investigates the evolution of the MZR and FMR at high redshift.

Findings

The MZR at z~1.4 is 3-5 times lower than the local universe.

The observed evolution aligns with a non-evolving FMR.

Using five lines yields more reliable metallicities than previous methods.

Abstract

A relation between the stellar mass M and the gas-phase metallicity Z of galaxies, the MZR, is observed up to higher redshifts. It is a matter of debate, however, if the SFR is a second parameter in the MZR. To explore this issue at z > 1, we used VLT-SINFONI near-infrared (NIR) spectroscopy of eight zCOSMOS galaxies at 1.3 < z < 1.4 to measure the strengths of four emission lines: Hbeta, [OIII]lambda5007, Halpha, and [NII]lambda6584, additional to [OII]lambda3727 measured from VIMOS. We derive reliable O/H metallicities based on five lines, and also SFRs from extinction corrected Halpha measurements. We find that the MZR of these star-forming galaxies at z~1.4 is lower than the local SDSS MZR by a factor of three to five, a larger change than reported in the literature using [NII]/Halpha-based metallicities from individual and stacked spectra. Correcting N2-based O/Hs using recent results by Newman et al. (2014), also the larger FMOS sample at z~1.4 of Zahid et al. (2014) shows a similar evolution of the MZR like the zCOSMOS objects. These observations seem also in agreement with a non-evolving FMR using the physically motivated formulation of the FMR from Lilly et al. (2013).