Evolution of the Ionizing Photon Luminosity Function

TL;DR

This paper discusses the importance of measuring the ionizing photon luminosity function up to redshift 1.2 to understand the sources of cosmic ionization, emphasizing the need for advanced multi-object spectroscopy on future observatories.

Contribution

It highlights the technical requirements and observational strategies needed to construct ionizing luminosity functions at intermediate redshifts using a proposed space-based multi-object spectrograph.

Findings

Feasibility of measuring ionizing photon escape fractions.

Design specifications for a suitable multi-object spectrograph.

Potential to improve understanding of cosmic reionization processes.

Abstract

Counting the number and brightness of ionizing radiation sources out to a redshift of z ~ 1.2 will revolutionize our understanding of how the ionizing background is created and sustained by the embedded growth of meta-galactic structures. The sheer number of sparsely separated targets required to efficiently construct redshift binned luminosity functions is industrial in scale, driving the need for low spectral resolution multi-object spectroscopy (MOS) with a short wavelength cut-off ~ 1000 {\AA}, a sensitivity in the far-UV to better than 30 abmag, and an instantaneous field-of-view ~ (2')$^2$. A MOS on Habitable Worlds Observatory is the only instrument that could conceivably carry out such an ambitious observing program. This program will quantify how much of the ionizing radiation produced by galaxies is attenuated by intervening neutral H, He and dust, and how much escapes to maintain the universe in a mostly ionized state.