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

Euclid and the Roman Space Telescope (Roman) will soon use grism spectroscopy to detect millions of galaxies via their H alpha and [O III] lambda 5007 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 H alpha and [O III] lambda 5007 luminosity functions between 1.16 < z < 1.90; this sample is similar to 4 times larger than previous studies at this redshift. We find very good agreement with previous measurements for H alpha, 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, L-*, increases monotonically with redshift, and use the H alpha luminosity function to calculate the epoch's cosmic star formation rate density. We find that H alpha-visible galaxies account for similar to 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.

Automated summary

Euclid and the Roman Space Telescope (Roman) will use grism spectroscopy to detect millions of galaxies via their H alpha and [O III] lambda 5007 emission. A sample of 4239 emission-line galaxies is used to measure the H alpha and [O III] lambda 5007 luminosity functions between 1.16 < z < 1.90. The results show good agreement with previous measurements for H alpha, but predict a higher number of intermediate-luminosity galaxies for [O III].