NIR spectroscopy of star-forming galaxies at z similar to 1.4 with Subaru/FMOS : The mass-metallicity relation.

Abstract

We present near-infrared spectroscopic observations of star-forming galaxies at z similar to 1.4 with FMOS on the Subaru Telescope. We observed K-band selected galaxies in the SXDS/UDS fields with K <= 23.9 mag, 1.2 <= z(ph) <= 1.6, M-* >= 10(9.5) M-circle dot, and expected F(H alpha) >= 10(-16) erg s(-1) cm(-2); 71 objects in the sample have significant detections of Ha. For these objects, excluding possible AGNs, identified from the BPT diagram, gas-phase metallicities were obtained from the [N II] / H alpha line ratio. The sample is split into three stellar-mass bins, and the spectra are stacked in each stellar-mass bin. The mass-metallicity relation obtained at z similar to 1.4 is located between those at z similar to 0.8 and z similar to 2.2. We constrain the intrinsic scatter to be similar to 0.1 dex, or larger in the mass-metallicity relation at z similar to 1.4; the scatter may be larger at higher redshifts. We found trends that the deviation from the mass-metallicity relation depends on the SFR (Star-formation rate) and the half light radius: Galaxies with higher SFR and larger half light radii show lower metallicities at a given stellar mass. One possible scenario for the trends is the infall of pristine gas accreted from IGM, or through merger events. Our data points show larger scatter than the fundamental metallicity relation (FMR) at z similar to 0.1, and the average metallicities slightly deviate from the FMR. The compilation of the mass-metallicity relations at z similar to 3 to z similar to 0.1 shows that they evolve smoothly from z similar to 3 to z similar to 0 without changing the shape so much, except for the massive part at z similar to 0.