The Hα and [O iii] λ5007 Luminosity Functions of 1.2 < z < 1.9 Emission-line Galaxies from Hubble Space Telescope (HST) Grism Spectroscopy

Abstract Euclid and the Roman Space Telescope (Roman) will soon use grism spectroscopy to detect millions of galaxies via their Hα and [O iii] λ5007 emission. To better constrain the expected galaxy counts from these instruments, we use a vetted sample of 4239 emission-line galaxies from the 3D Hubble Space Telescope survey to measure the Hα and [O iii] λ5007 luminosity functions between 1.16 < z < 1.90; this sample is ∼4 times larger than previous studies at this redshift. We find very good agreement with previous measurements for Hα, but for [O iii], we predict a higher number of intermediate-luminosity galaxies than from previous works. We find that, for both lines, the characteristic luminosity,  * , increases monotonically with redshift, and use the Hα luminosity function to calculate the epoch’s cosmic star formation rate density. We find that Hα-visible galaxies account for ∼81% of the epoch’s total star formation rate, and this value changes very little over the 1.16 < z < 1.56 redshift range. Finally, we derive the surface density of galaxies as a function of limiting flux and find that previous predictions for galaxy counts for the Euclid Wide Survey are unchanged, but there may be more [O iii] galaxies in the Roman High Latitude Survey than previously estimated.