Misc,
Binary Stars Can Provide the "Missing Photons" Needed for Reionization
(2016)cite arxiv:1601.07559Comment: 6 pages, 3 figures, submitted to MNRAS Letter.
Abstract
Empirical constraints on reionization require galactic ionizing photon escape
fractions fesc>20%, but recent high-resolution radiation-hydrodynamic
calculations have consistently found much lower values ~1-5%. While these
models have included strong stellar feedback and additional processes such as
runaway stars, they have almost exclusively considered stellar evolution models
based on single (isolated) stars, despite the fact that most massive stars are
in binaries. We re-visit these calculations, combining radiative transfer and
high-resolution cosmological simulations of galaxies with detailed models for
stellar feedback from the Feedback in Realistic Environments (FIRE) project.
For the first time, we use a stellar evolution model that includes a physically
and observationally motivated treatment of binaries (the BPASS model). Binary
mass transfer and mergers enhance the population of massive stars at late times
(>3 Myr) after star formation, which in turn strongly enhances the late-time
ionizing photon production (especially at low metallicities). These photons are
produced after feedback from massive stars has carved escape channels in the
ISM, and so efficiently leak out of galaxies. As a result, the time-averaged
"effective" escape fraction (ratio of escaped ionizing photons to observed 1500
A photons) increases by factors 4-10, sufficient to explain reionization. While
important uncertainties remain, we conclude that binary evolution may be
critical for understanding the ionization of the Universe.
