The relationship between stellar populations and the ionizing flux with which they irradiate their surroundings has profound implications for the evolution of the intergalactic medium .
We quantify the ionizing flux arising from synthetic stellar populations which incorporate the evolution of interacting binary stars .
We determine that these show ionizing flux boosted by 60 per cent at 0.05 \leq Z \leq 0.3 Z _ { \odot } and a more modest 10-20 per cent at near-Solar metallicities relative to star-forming populations in which stars evolve in isolation .
The relation of ionizing flux to observables such as 1500Å continuum and ultraviolet spectral slope is sensitive to attributes of the stellar population including age , star formation history and initial mass function .
For a galaxy forming 1 M _ { \odot } yr ^ { -1 } , observed at > 100 Myr after the onset of star formation , we predict a production rate of photons capable of ionizing hydrogen , N _ { \mathrm { ion } } = 1.4 \times 10 ^ { 53 } s ^ { -1 } at Z = Z _ { \odot } and 3.5 \times 10 ^ { 53 } s ^ { -1 } at 0.1 Z _ { \odot } , assuming a Salpeter-like initial mass function .
We evaluate the impact of these issues on the ionization of the intergalactic medium , finding that the known galaxy populations can maintain the ionization state of the Universe back to z \sim 9 , assuming that their luminosity functions continue to M _ { UV } = -10 , and that constraints on the intergalactic medium at z \sim 2 - 5 can be satisfied with modest Lyman continuum photon escape fractions of 4 - 24 per cent depending on assumed metallicity .