The H$\alpha$ and [O III] $\lambda 5007$ Luminosity Functions of $1.2<z<1.9$ Emission-Line Galaxies from HST Grism Spectroscopy

TL;DR

This study measures Hα and [O III] luminosity functions of emission-line galaxies at redshifts 1.16 to 1.90, providing insights for upcoming Euclid and Roman Space Telescope surveys and revealing an increase in characteristic luminosity with redshift.

Contribution

It presents the largest sample to date for this redshift range, improving luminosity function estimates and predicting galaxy counts for future space telescope surveys.

Findings

Good agreement with previous Hα measurements.

Higher intermediate-luminosity [O III] galaxy counts than prior studies.

Hα luminosity function indicates a stable contribution to star formation rate density.

Abstract

Euclid and the Roman Space Telescope (Roman) will soon use grism spectroscopy to detect millions of galaxies via H$\alpha$ and [O III] $\lambda 5007$ emission. To better constrain the expected galaxy counts from these instruments, we use a vetted sample of 4,239 emission-line galaxies from the 3D-HST survey to measure the H$\alpha$ and [O III] $\lambda 5007$ luminosity functions between $1.16<z<1.90$; this sample is $\sim 4$ 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 previous works. We find that for both lines, the characteristic luminosity, $\mathcal{L}_*$, 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 $\sim 81\%$ 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.