Recent studies show that the comic star-formation history has a peak epoch at z=1-3
("Cosmic high noon"). It is also known that the AGN activity is the highest and the
well-ordered morphology such as the "Hubble sequence" emerges in this redshift
range. Gas metallicity, which is normally measured from strong optical emission lines,
is also an important parameter for understanding the past star-formation activity
including gas inflow and outflow. Measuring metallicity of a large sample of galaxies at
z>1, however, is difficult because the emission lines used to evaluate the metallicity
are redshifted to NIR wavelength regime. 

Recently, we conducted a large NIR survey by using Fibre-Multi Object Spectrograph
(FMOS) on the Subaru Telescope. We detected significant Ha emission lines of ~340
star-forming galaxies at z=1.2-1.6 in the Subaru XMM-Newton Deep Survey and UKIDSS Ultra
Deep Survey (SXDS/UDS) field. The metallicity is measured from the [NII]/Ha line ratio,
and the correlation between stellar mass and metallicity (mass-metallicity relation) in
this redshift range is examined. Comparing to the previous observational results, the
mass-metallicity relation evolves smoothly from z~3 to z~0.1, i.e., the metallicity
increases with decreasing redshift at a fixed stellar mass. The obtained
mass-metallicity relation is in good agreement with the prediction of a cosmological
simulation with strong galactic wind models. We examined the gas inflow and outflow
rates from the obtained metallicity, stellar mass, and the gas mass fraction (derived
from Ha luminosity assuming the Kennicutt-Schmidt law) by comparing to a simple analytic
model of chemical evolution. We found that the inflow and outflow rates are comparable
to or larger than the SFR. By applying the same method to the sample in the previous
works at z~0 and z~2, we also found that both inflow rate and outflow rates increase
with increasing redshift, which indicates that the gas flowing process is more active at
higher redshift.