The [O III]λ5007 equivalent width distribution at z ∼ 2: the redshift evolution of the extreme emission line galaxies

We determine the [O III]lambda 5007 equivalent width (EW) distribution of 1.700 < z < 2.274 rest-frame ultraviolet (UV)-selected (M-UV < -19) star-forming galaxies in the GOODS North and South fields. We make use of deep HDUV broad-band photometry catalogues for selection and 3D-HST WFC3/IR grism spectra for measurement of line properties. The [O III]lambda 5007 EW distribution allows us to measure the abundance of extreme emission line galaxies (EELGs) within this population. We model a lognormal distribution to the [O III]lambda 5007 rest-frame EWs of galaxies in our sample, with location parameter mu = 4.24 +/- 0.07 and variance parameter sigma = 1.33 +/- 0.06. This EW distribution has a mean [O III]lambda 5007 EW of 168 +/- 1 angstrom. The fractions of z similar to 2 rest-UV-selected galaxies with [O III]lambda 5007 EWs greater than 500, 750, and 1000 angstrom are measured to be 6.8(-0.9)(+1.0) per cent, 3.61(-0.6)(+0.7) per cent, and 2.2(-0.4)(+0.5) per cent, respectively. The EELG fractions do not vary strongly with UV luminosity in the range (-21.6 < M-UV < -19.0) considered in this paper, consistent with findings at higher redshifts. We compare our results to z similar to 5 and z similar to 7 studies, where candidate EELGs have been discovered through Spitzer/IRAC colours, and we identify rapid evolution with redshift in the fraction of star-forming galaxies observed in an extreme emission line phase (a rise by a factor similar to 10 between z similar to 2 and z similar to 7). This evolution is consistent with an increased incidence of strong bursts in the galaxy population of the reionization era. While this population makes a sub-dominant contribution of the ionizing emissivity at z similar or equal to 2, EELGs are likely to dominate the ionizing output in the reionization era.