2017ApJ...845..111M

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, for attempting to detect LyC escaping star-forming galaxies for redshifts z 3. Examples are given that relate the integrated escape fraction (f^e_LyC) of ionizing photons, obtained by integrating over the entire extreme UV (EUV) bandpass, to the relative escape fraction (f^e₉₀₀) observed just shortward of the ionization edge at 911.8 Å as a function of H I, He I, and He II column densities. We find that for logN_HI(cm^–2) 17.0, f^e_LyC is significantly greater than f^e₉₀₀. 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 metagalactic ionizing background (MIB).