SCORCH. II. Radiation-hydrodynamic Simulations of Reionization with Varying Radiation Escape Fractions

In the Simulations and Constructions of the Reionization of Cosmic Hydrogen project, we present new radiation-hydrodynamic simulations with updated high-redshift galaxy populations and varying radiation escape fractions. The simulations are designed to have fixed Thomson optical depth τ ≈ 0.06, consistent with recent Planck observations, and similar midpoints of reionization 7.5 ≲ z ≲ 8.0, but with different ionization histories. The galaxy luminosity functions and ionizing photon production rates in our model are in good agreement with recent HST observations. Adopting a power-law form for the radiation escape fraction {f}_esc}(z)={f}₈{[(1+z)/9]}^{a₈}, we simulate the cases for a ₈ = 0, 1, and 2 and find a ₈ ≲ 2 in order to end reionization in the range of 5.5 ≲ z ≲ 6.5 to be consistent with Lyα forest observations. At fixed τ and as the power-law slope a ₈ increases, the reionization process starts earlier but ends later with a longer duration Δz and the decreased redshift asymmetry Az. We find a range of durations 3.9 ≲ Δz ≲ 4.6 that is currently in tension with the upper limit Δz < 2.8 inferred from a recent joint analysis of Planck and South Pole Telescope observations.