A large, deep 3 deg2 survey of Hα, [OIII], and [OII] emitters from LAGER: Constraining luminosity functions

Abstract

We present our measurements of the Ha, [OIII], and [O II] luminosity functions as part of the Lyman Alpha Galaxies at Epoch of Reionization (LAGER) survey using our samples of 1577 z=0.47Hα-, 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∗ = 10-3.16+0.09-0.09 Mpc-3 and L∗ = 1041.72+0.09-0.09 erg s-1 for Hα, φ∗ = 10-2.16+0.10-0.12 Mpc-3 and L∗ = 1041.38+0.07-0.06 erg s-1 for [O III], and φ∗ = 10-1.97+0.07-0.07 Mpc-3 and L∗= 1041.66+0.03-0.03 erg s-1 for [OII], 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 AHα = 1 mag. We also design our own empirical restframe g - r calibration using SDSS DR12 data, test it against our z = 0.47 Hα emitters with zCOSMOS 1D spectra, and calibrate it for (g - r) between -0.8 and 1.3 mag. Dust and AGNcorrected star formation rate densities (SFRDs) are measured as log10ρSFR/(M⊙yr-1 Mpc-3)= -1.63 ± 0.04, -1.07 ± 0.06, and -0.90 ± 0.10 for Ha, [OIII], 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 Ha sample traces ~70 per cent of the total z = 0.47 SFRD.