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 ≤ zph ≤ 1.6 in the Subaru XMM–Newton Deep Survey/Ultra Deep Survey fields with M* ≥ 109.5 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.