We present a sample of \sim 1000 emission line galaxies at z = 0.4 - 4.7 from the \sim 0.7 deg ^ { 2 } High- z Emission Line Survey ( HiZELS ) in the Boötes field identified with a suite of six narrow-band filters at \approx 0.4 - 2.1 \mu m. These galaxies have been selected on their Ly \alpha ( 73 ) , [ Oii ] ( 285 ) , H \beta / [ Oiii ] ( 387 ) or H \alpha ( 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 .
[ O ii ] -H \alpha ) detections and/or spectroscopy .
In this survey paper , we present the observations , selection and catalogs of emitters .
We measure number densities of Ly \alpha , [ O ii ] , H \beta / [ Oiii ] and H \alpha and confirm strong luminosity evolution in star-forming galaxies from z \sim 0.4 to \sim 5 , in agreement with previous results .
To demonstrate the usefulness of dual-line emitters , we use the sample of dual [ O ii ] -H \alpha emitters to measure the observed [ O ii ] /H \alpha ratio at z = 1.47 .
The observed [ O ii ] /H \alpha ratio increases significantly from 0.40 \pm 0.01 at z = 0.1 to 0.52 \pm 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 H \alpha and Ly \alpha number densities at z \approx 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 \approx 100 % at line-luminosities L \gtrsim 3 \times 10 ^ { 44 } erg s ^ { -1 } .