Kavli Affiliate: Martin Haehnelt
| First 5 Authors: Joakim Rosdahl, Jérémy Blaizot, Harley Katz, Taysun Kimm, Thibault Garel
| Summary:
We measure escape fractions, $f_{rm esc}$, of ionizing radiation from
galaxies in the SPHINX suite of cosmological radiation-hydrodynamical
simulations of reionization, resolving halos with $M_{rm vir} gtrapprox 7.5
times 10^7 M_{odot}$ with a minimum cell width of $approx 10$ pc. Our new
and largest $20$ co-moving Mpc wide volume contains tens of thousands of
star-forming galaxies with halo masses up to a few times $10^{11} M_{odot}$.
The simulated galaxies agree well with observational constraints of the UV
luminosity function in the Epoch of Reionization. The escape fraction
fluctuates strongly in individual galaxies over timescales of a few Myrs, due
to its regulation by supernova and radiation feedback, and at any given time a
tiny fraction of star-forming galaxies emits a large fraction of the ionizing
radiation escaping into the inter-galactic medium. Statistically, $f_{rm esc}$
peaks in intermediate-mass, intermediate-brightness, and low-metallicity
galaxies ($M_{*} approx 10^7 M_{odot}$, $M_{1500} approx -17$, $Zlesssim
5 times 10^{-3} Z_{odot}$), dropping strongly for lower and higher masses,
brighter and dimmer galaxies, and more metal-rich galaxies. The escape fraction
correlates positively with both the short-term and long-term specific star
formation rate. According to SPHINX, galaxies too dim to be yet observed, with
$M_{1500} gtrapprox -17$, provide about $55$ percent of the photons
contributing to reionization. The global averaged $f_{rm esc}$ naturally
decreases with decreasing redshift, as predicted by UV background models and
low-redshift observations. This evolution is driven by decreasing specific star
formation rates over cosmic time.
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