THE STELLAR POPULATION AND STAR FORMATION RATES OF z ≈ 1.5-1.6 [O II]-EMITTING GALAXIES SELECTED FROM NARROWBAND EMISSION-LINE SURVEYS

We present the first detailed study of the stellar populations of star-forming galaxies at z ∼ 1.5, which are selected by their [O II] emission line, detected in narrowband surveys. We identified ∼1300 [O II] emitters at z = 1.47 and z = 1.62 in the Subaru Deep Field with rest-frame equivalent widths (EWs) above 13 Å. Optical and near-infrared spectroscopic observations for ≈10% of our samples show that our separation of [O II] from [O III] emission-line galaxies in two-color space is 99% successful. We analyze the multi-wavelength properties of a subset of ∼1200 galaxies with the best photometry. They have average rest-frame EW of 45 Å, stellar mass of 3 × 109 M☉, and stellar age of 100 Myr. In addition, our spectral energy distribution (SED) fitting and broadband colors indicate that [O II] emitters span the full range of galaxy populations at z ∼ 1.5. We also find that 80% of [O II] emitters are also photometrically classified as 'BX/BM' (UV) galaxies and/or the star-forming 'BzK' (near-IR) galaxies. Our [O II] emission line survey produces a far more complete and somewhat deeper sample of z ∼ 1.5 galaxies than either the BX/BM or sBzK selection alone. We constructed average SEDs and find that higher [O II] EW galaxies have somewhat bluer continua. SED model-fitting shows that they have on average half the stellar mass of galaxies with lower [O II] EW. The observed [O II] luminosity is well correlated with the far-UV continuum with a logarithmic slope of 0.89 ± 0.22. The scatter of the [O II] luminosity against the far-UV continuum suggests that [O II] can be used as a star formation rate indicator with a reliability of 0.23 dex.