A large, deep 3 deg² survey of H α, [O III], and [O II] emitters from LAGER: constraining luminosity functions

Abstract

We present our measurements of the H α, [O III], and [O II] luminosity functions as part of the Lyman Alpha Galaxies at Epoch of Reionization (LAGER) survey using our samples of 1577 z = 0.47 H α-, 3933 z = 0.93 [O III]-, and 5367 z = 1.59 [O II]-selected emission line galaxies in a 3 deg² single, CTIO/Blanco DECam pointing of the COSMOS field. Our observations reach 5σ depths of 8.2 × 10^-18 erg s^-1 cm^-2 and comoving volumes of (1-7) × 10⁵ Mpc³ making our survey one of the deepest narrow-band surveys. We select our emission line galaxies via spectroscopic confirmation, photometric redshifts, and colour-colour selections. We measure the observed luminosity functions for each sample and find best fits of φ ^\star = 10^{-3.16^{+0.09}_{-0.09}} Mpc^-3 and L^\star = 10^{41.72^{+0.09}_{-0.09}} erg s^-1 for H α, φ ^\star = 10^{-2.16^{+0.10}_{-0.12}} Mpc^-3 and L^\star = 10^{41.38^{+0.07}_{-0.06}} erg s^-1 for [O III], and φ ^\star = 10^{-1.97^{+0.07}_{-0.07}} Mpc^-3 and L^\star = 10^{41.66^{+0.03}_{-0.03}} erg s^-1 for [O II], with α fixed to -1.75, -1.6, and -1.3, respectively. An excess of bright >10⁴² erg s^-1 [O III] emitters is observed and may be due to active galactic nucleus (AGN) contamination. Corrections for dust attenuation are applied assuming A_Hα = 1 mag. We also design our own empirical rest-frame g - r calibration using SDSS DR12 data, test it against our z = 0.47 H α emitters with zCOSMOS 1D spectra, and calibrate it for (g - r) between -0.8 and 1.3 mag. Dust and AGN-corrected star formation rate densities (SFRDs) are measured as log₁₀ρ_SFR/(M_⊙ yr^-1 Mpc^-3) = -1.63 ± 0.04, -1.07 ± 0.06, and -0.90 ± 0.10 for H α, [O III], and [O II], respectively. We find our [O III] and [O II] samples fully trace cosmic star formation activity at their respective redshifts in comparison to multiwavelength SFRDs, while the H α sample traces ∼70 per cent of the total z = 0.47 SFRD.