SCORCH. II. Radiation-Hydrodynamic simulations of reionization with varying radiation escape fractions

Abstract

In the Simulations and Constructions of the Reionization of Cosmic Hydrogen (SCORCH) 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 $\tau \approx 0.06$, consistent with recent Planck observations, and similar midpoints of reionization $7.5 \lesssim z \lesssim 8.0$, 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 $f_{\text{esc}}(z) = f_8[(1+z)/9]^{a_{8}}$, we simulate the cases for $a_8 = 0$, 1, and 2 and find $a_8 \lesssim 2$ in order to end reionization in the range $5.5 \lesssim z \lesssim 6.5$ to be consistent with Lyman alpha forest observations. At fixed $\tau$ and as the power-law slope $a_8$ increases, the reionization process starts earlier but ends later with a longer duration $\Delta z$ and the decreased redshift asymmetry $Az$. We find a range of durations $3.9 \lesssim \Delta z \lesssim 4.6$ that is currently in tension with the upper limit $\Delta z < 2.8$ inferred from a recent joint analysis of Planck and South Pole Telescope observations.