Stellar Population Effects on the Inferred Photon Density at Reionization

Understand

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 < Z < 0.3 Z_sun 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 1500A continuum and ultraviolet spectral slope is sensitive to attributes of the stellar population including age, star formation history and initial mass function.