Boötes-HiZELS: An optical to near-infrared survey of emission-line galaxies at z = 0.4 − 4.7

We present a sample of ∼ 1000 emission line galaxies at z = 0.4 − 4.7 from the ∼ 0.7deg² High-z Emission Line Survey (HiZELS) in the Boötes field identified with a suite of six narrow-band filters at ≈ 0.4−2.1 µm. These galaxies have been selected on their Lyα (73), [Oii] (285), Hβ/[Oiii] (387) or Hα (362) emission-line, and have been classified with optical to near-infrared colours. A subsample of 98 sources have reliable redshifts from multiple narrow-band (e.g. [Oii]-Hα) detections and/or spectroscopy. In this survey paper, we present the observations, selection and catalogs of emitters. We measure number densities of Lyα, [Oii], Hβ/[Oiii] and Hα and confirm strong luminosity evolution in star-forming galaxies from z ∼ 0.4 to ∼ 5, in agreement with previous results. To demonstrate the usefulness of dual-line emitters, we use the sample of dual [Oii]-Hα emitters to measure the observed [Oii]/Hα ratio at z = 1.47. The observed [Oii]/Hα ratio increases significantly from 0.40±0.01 at z = 0.1 to 0.52±0.05 at z = 1.47, which we attribute to either decreasing dust attenuation with redshift, or due to a bias in the (typically) fiber-measurements in the local Universe which only measure the central kpc regions. At the bright end, we find that both the Hα and Lyα number densities at z ≈ 2.2 deviate significantly from a Schechter form, following a power-law. We show that this is driven entirely by an increasing X-ray/AGN fraction with line-luminosity, which reaches ≈ 100 % at line-luminosities L & 3 ×10⁴⁴ erg s⁻¹.