Flux sensitivity requirements for the detection of Lyman continuum radiation drop-ins from star-forming galaxies below redshifts of 3

TL;DR

This paper estimates the flux sensitivity needed to detect Lyman continuum radiation escaping from star-forming galaxies below redshift 3, aiding future observational strategies and instrument design.

Contribution

It provides flux estimates based on galaxy luminosities and escape fractions, relating observed and absolute escape fractions considering intergalactic medium absorption.

Findings

Flux estimates guide detection strategies for LyC escape.

Detection of LyC drop-ins improves understanding of ionizing photon escape.

Flux sensitivity requirements vary with HI column density and redshift.

Abstract

Flux estimates for ionizing radiation escaping from star-forming galaxies with characteristic UV luminosities ($L^{*}_{1500(1+z)}$) derived from GALEX and the VIMOS-VLT Deep Survey, are presented as a function of redshift and assumed escape fraction. These estimates offer guidance to the design of instrumentation and observing strategies, be they spectroscopic or photometric, attempting to detect LyC escaping star-forming galaxies for redshifts $ z < 3$. Examples are given that relate the absolution escape fraction ($f^{e}_{LyC}$) of ionizing photons, integrated over the entire extreme UV (EUV) bandpass, to the relative escape fraction ($f^{e}_{900}$) observed just shortward of the ionization edge at 911.8 \AA\ as a function of HI, HeI, and HeII column densities. We find that for $\log{N_{HI}(cm^{-2})} \gtrsim 17.0$ $f^{e}_{LyC}$ is significantly greater than $f^{e}_{900}$. Detection of LyC "drop-ins" in the rest-frame EUV will provide enhanced fidelity to determinations of the integrated fraction of ionizing photons $f^{e}_{LyC}$ that escape star-forming galaxies and contribute to the meta-galactic ionizing background.