The mass-metallicity relation at z ∼ 1.4 revealed with Subaru/FMOS

Abstract

We present a stellar mass-metallicity relation at z ∼ 1.4 with an unprecedentedly large sample of ∼340 star-forming galaxies obtained with Fibre Multi-Object Spectrograph (FMOS) on the Subaru Telescope. We observed K-band selected galaxies at 1.2 ≤ z_ph ≤ 1.6 in the Subaru XMM-Newton Deep Survey/Ultra Deep Survey fields with M_* ≥ 10^9.5 M_⊙, and expected F(Hα) ≥ 5 × 10^-17 erg s^-1 cm^-2. Among the observed ∼1200 targets, 343 objects show significant Hα emission lines. The gas-phase metallicity is obtained from [N II] λ6584/Hα line ratio, after excluding possible active galactic nuclei. Due to the faintness of the [N II] λ6584 lines, we apply the stacking analysis and derive the mass-metallicity relation at z ∼ 1.4. Our results are compared to past results at different redshifts in the literature. The mass-metallicity relation at z ∼ 1.4 is located between those at z ∼ 0.8 and z ∼ 2.2; it is found that the metallicity increases with decreasing redshift from z ∼ 3 to z ∼ 0 at fixed stellar mass. Thanks to the large size of the sample, we can study the dependence of the mass-metallicity relation on various galaxy physical properties. The average metallicity from the stacked spectra is close to the local Fundamental Metallicity Relation (FMR) in the higher metallicity part but ≳ 0.1 dex higher in metallicity than the FMR in the lower metallicity part. We find that galaxies with larger E(B - V), B - R and R - H colours tend to show higher metallicity by ∼0.05 dex at fixed stellar mass. We also find relatively clearer size dependence that objects with smaller half-light radius tend to show higher metallicity by ∼0.1 dex at fixed stellar mass, especially in the low-mass part.