Abstract
Abstract High-resolution numerical simulations including feedback and aimed at calculating the escape fraction (f esc) of hydrogen-ionizing photons often assume stellar radiation based on single-stellar population synthesis models. However, strong evidence suggests the binary fraction of massive stars is ≳70%. Moreover, simulations so far have yielded values of f esc falling only on the lower end of the ∼10%–20% range, the amount presumed necessary to reionize the universe. Analyzing a high-resolution (4 pc) cosmological radiation-hydrodynamic simulation, we study how f esc changes when we include two different products of binary stellar evolution—stars stripped of their hydrogen envelopes and massive blue stragglers. Both produce significant amounts of ionizing photons 10–200 Myr after each starburst. We find the relative importance of these photons to be amplified with respect to escaped ionizing photons, because peaks in star formation rates (SFRs) and f esc are often out of phase by this 10–200 Myr. Additionally, low-mass, bursty galaxies emit Lyman continuum radiation primarily from binary products when SFRs are low. Observations of these galaxies by the James Webb Space Telescope could provide crucial information on the evolution of binary stars as a function of redshift. Overall, including stripped stars and massive blue stragglers increases our photon-weighted mean escape fraction ( ) by ∼13% and ∼10%, respectively, resulting in . Our results emphasize that using updated stellar population synthesis models with binary stellar evolution provides a more sound physical basis for stellar reionization.
Highlights
High-redshift, star-forming, dwarf galaxies with virial masses that range from 108 − 1010.5 M are the most plausible source of the hydrogen-ionizing radiation responsible for the reionization of the Universe by z ∼ 6, provided a high enough escape fraction (Haehnelt et al 2001; Cowie et al 2009; Fontanot et al 2014; Madau & Fragos 2017; Madau & Haardt 2015)
We use one halo to illustrate some basic effects on the escape fraction of ionizing photon due to binary evolution in Figures 2 and 3
Using ultra-high resolution cosmological radiationhydrodynamic simulations, we study the effects of interacting binaries on the fraction of LyC photons that escape from their host galaxy
Summary
High-redshift, star-forming, dwarf galaxies with virial masses that range from 108 − 1010.5 M are the most plausible source of the hydrogen-ionizing radiation responsible for the reionization of the Universe by z ∼ 6, provided a high enough escape fraction (fesc) (Haehnelt et al 2001; Cowie et al 2009; Fontanot et al 2014; Madau & Fragos 2017; Madau & Haardt 2015). Observations of Lyman continuum (LyC) in the local Universe, which is limited to starburst galaxies, generally suggest low escape fractions of 8% (Leitet et al 2011, 2013; Borthakur et al 2014; Leitherer et al 2016; Izotov et al 2016). Star-forming galaxies at z ∼ 1 with LyC detections show low escape fractions of a few percent (Siana et al 2007, 2010; Bridge et al 2010; Rutkowski et al 2016). The average relative escape fraction, the ratio of the escape fraction of 990 ̊A to 1500 ̊A photons, is found to be small
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