MOSEL: Strong [OIII] 5007 A Emitting Galaxies at (3 < z < 4) from the ZFOURGE Survey

Abstract

To understand how strong emission-line galaxies (SELGs) contribute to the overall growth of galaxies and star formation history of the universe, we target SELGs from the ZFOURGE imaging survey that have blended Hβ+[O iii] rest-frame equivalent widths of >230 A and 2.5 < ${z}_{\mathrm{phot}}$ < 4.0. Using Keck/MOSFIRE, we measure 49 redshifts for galaxies brighter than K s = 25 mag as part of our Multi-Object Spectroscopic Emission Line (MOSEL) survey. Our spectroscopic success rate is ~53% and ${z}_{\mathrm{phot}}$ uncertainty is ${\sigma }_{z}$ = [Δz/(1+z)] = 0.0135. We confirm 31 ELGs at $3\lt {z}_{\mathrm{spec}}\lt 3.8$, and show that SELGs have spectroscopic rest-frame [O iii]5007 A equivalent widths of 100-500 A and tend to be lower-mass systems [$\mathrm{log}({M}_{\star }/{M}_{\odot })$ ~ 8.2-9.6] compared with more typical star-forming galaxies. The SELGs lie ~0.9 dex above the star-forming main sequence at z ~ 3.5 and have high inferred gas fractions of ${f}_{\mathrm{gas}}$ gsim 60%, i.e., the inferred gas masses can easily fuel a starburst to double stellar masses within ~10-100 Myr. Combined with recent results using ZFOURGE, our analysis indicates that (1) strong [O iii]5007 A emission signals an early episode of intense stellar growth in low-mass [${M}_{\star }\lt 0.1\,{M}^{\star }$] galaxies and (2) many, if not most, galaxies at z > 3 go through this starburst phase. If true, low-mass galaxies with strong [O iii]5007 A emission (EWrest > 200 A) may be an increasingly important source of ionizing UV radiation at z > 3. Show more