Predicting the redshift 2 Halpha luminosity function using [OIII] emission line galaxies

TL;DR

This paper estimates the number of Halpha emitters at z~2 observable by future space surveys using [OIII] emission line galaxies data from the WISP survey, aiding in dark energy research.

Contribution

It introduces a method to derive Halpha luminosity functions from [OIII] data and predicts galaxy counts for upcoming surveys at high redshift.

Findings

Approximately 3000 galaxies/deg^2 at z~2 for Euclid's flux limit.

Around 20,000 galaxies/deg^2 at z~2 for WFIRST's baseline flux limit.

The [OIII]-based method effectively predicts Halpha counts at high redshift.

Abstract

Upcoming space-based surveys such as Euclid and WFIRST-AFTA plan to measure Baryonic Acoustic Oscillations (BAOs) in order to study dark energy. These surveys will use IR slitless grism spectroscopy to measure redshifts of a large number of galaxies over a significant redshift range. In this paper, we use the WFC3 Infrared Spectroscopic Parallel Survey (WISP) to estimate the expected number of Halpha (Ha) emitters observable by these future surveys. WISP is an ongoing HST slitless spectroscopic survey, covering the 0.8-1.65micron wavelength range and allowing the detection of Ha emitters up to z~1.5 and [OIII] emitters to z~2.3. We derive the Ha-[OIII] bivariate line luminosity function for WISP galaxies at z~1 using a maximum likelihood estimator that properly accounts for uncertainties in line luminosity measurement, and demonstrate how it can be used to derive the Ha luminosity function from exclusively fitting [OIII] data. Using the z~2 [OIII] line luminosity function, and assuming that the relation between Ha and [OIII] luminosity does not change significantly over the redshift range, we predict the Ha number counts at z~2 - the upper end of the redshift range of interest for the future surveys. For the redshift range 0.7<z<2, we expect ~3000 galaxies/deg^2 for a flux limit of 3x10^{-16} ergs/s/cm^2 (the proposed depth of Euclid galaxy redshift survey) and ~20,000 galaxies/deg^2 for a flux limit of ~10^{-16} ergs/s/cm^2 (the baseline depth of WFIRST galaxy redshift survey).