The [OIII]$\lambda5007$ equivalent width distribution at z $\sim2$: The redshift evolution of the extreme emission line galaxies

Abstract

We determine the [OIII]𝜆5007 equivalent width (EW) distribution of 1.700 < z < 2.274 rest-frame UV-selected (M UV < −19) star-forming galaxies in the GOODS North and South fields. We make use of deep HDUV broadband photometry catalogues for selection and 3D-HST WFC3/IR grism spectra for measurement of line properties. The [OIII]𝜆5007 EW distribution allows us to measure the abundance of extreme emission line galaxies (EELGs) within this population. We model a log-normal distribution to the [OIII]𝜆5007 rest-frame equivalent widths of galaxies in our sample, with location parameter 𝜇 = 4.24 ± 0.07 and variance parameter 𝜎 = 1.33 ± 0.06. This EW distribution has a mean [OIII]𝜆5007 EW of 168±1 Å. The fractions of z ∼ 2 rest-UV-selected galaxies with [OIII]𝜆5007 EWs greater than 500, 750 and 1000 Å are measured to be 6.8 +1.0 −0.9 %, 3.6 +0.7 −0.6 %, and 2.2 +0.5 −0.4 % 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 ∼ 5 and z ∼ 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 ∼ 10 between z ∼ 2 and z ∼ 7). This evolution is consistent with an increased incidence of strong bursts in the galaxy population of the reionisation era. While this population makes a sub-dominant contribution of the ionising emissivity at z 2, EELGs are likely to dominate the ionising output in the reionisation era.

The Low-redshift Lyman Continuum Survey. II. New Insights into LyC Diagnostics

“…Other properties may readily persist at higher redshifts (e.g., Hβ EW, [O III] λ5007 EW, O 32 , R 23 ; see Nakajima et al 2020;Boyett et al 2021;Endsley et al 2021;Reddy et al 2022;Saxena et al 2022) but are difficult to observe at z  6 without space-based facilities like JWST. However, as we enter the JWST era, indirect indicators of f esc LyC will prove immensely useful via the trends presented in Section 3.…”

The Low-Redshift Lyman Continuum Survey II: New Insights into LyC Diagnostics

“…Other properties may readily persist at higher redshifts (e.g., Hβ EW, [O III]λ5007 EW, O 32 , R 23 , cf. Nakajima et al 2020;Boyett et al 2021;Endsley et al 2021;Reddy et al 2021;Saxena et al 2021) but are difficult to observe at z 6 without space-based facilities like JWST. However, as we enter the JWST era, indirect indicators of f LyC esc will prove immensely useful via the trends presented in §3.…”

Subaru/HSC z-Broadband Excess Selection of Extreme Emission Line Galaxies at z<1

“…We will refer to these galaxies as EELGs in reference to their extreme EWs. EELGs are easy to identify in grism observations (Atek et al 2011;Maseda et al 2018;Boyett et al 2021), which have confirmed a steep positive evolution in their number density from the local value to higher redshifts (Noeske et al 2006). More recent studies have used slit-based spectroscopy to push these measurements to redshift z ≈ 7 and beyond (Endsley et al 2021).…”