The nature of Hα+[O III]and [O II] emitters to z ~ 5 with HiZELS: Stellar mass functions and the evolution of EWs

Abstract

We investigate the properties of ~7000 narrow-band selected galaxies with strong Hα+[O iii] and [Oii] nebular emission lines from the High-z Emission-Line Survey between z ~ 0.8 and 5.0. Our sample covers a wide range in stellar mass (Mstellar ~ 107.5-12.0 M⊙), rest-frame equivalent widths (EWrest~10-105 Å), and line luminosities (Lline ~ 1040.5-43.2 erg s-1). We measure the Hα+[OIII]-selected stellar mass functions out to z ~ 3.5 and find that both M* and φ* increases with cosmic time. The [OII]-selected stellar mass functions show a constant M* ≈ 1011.6M˙ and a strong, increasing evolution with cosmic time in φ* in line with HA studies. We also investigate the evolution of the EWrest as a function of redshift with a fixed mass range (109.5-10.0 M⊙) and find an increasing trend best represented by (1 + z)3.81± 0.14 and (1 + z)2.72± 0.19 up to z ~ 2 and ~3for HBα[Oiii] and [Oii] emitters, respectively. This is the first time that the EWrest evolution has been directly measured for Hα[O iii] and [O ii] emitters up to these redshifts. There is evidence for a slower evolution for z > 2inthe Hα+[OIII]EWrest and a decreasing trend for z> 3inthe [OII]EWrest evolution, which would imply low [Oii] EW at the highest redshifts and higher [Oiii]/[Oii] line ratios. This suggests that the ionization parameter at higher redshift may be significantly higher than the local Universe. Our results set the stage for future near-IR space-based spectroscopic surveys to test our extrapolated predictions and also produce z> 5 measurements to constrain the high-z end of the EWrest and [Oiii]/[Oii] evolution.