I will review our study of 1500 galaxies in the COSMOS field at 1.4 < z < 1.7 that covers 1.5 square degrees with the Fiber Multi-Object Spectrograph on Subaru Telescope. Such high multiplex near-infrared spectrographs on 8-10m class telescopes are now providing new insight on the conditions of the interstellar medium in high-redshift galaxies using well-understood rest-frame optical emission lines. We find an evolution of the ISM properties with respect to the level of chemical enrichment, ionization state, and density over a broad range in stellar mass. I’ll highlight the effectiveness of our wide-field survey to probe the rarer populations such as massive galaxies, starbursts and AGNs. Furthermore, we provide an estimate of the surface density of bright Halpha emitters relevant for future BAO studies at high-z with Euclid and WFIRST.