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

TL;DR

This paper presents radiation-hydrodynamic simulations of cosmic reionization with varying escape fractions, showing how different models affect the timing and duration of reionization, and comparing results with observational constraints.

Contribution

The study introduces new simulations with variable escape fractions that match observed reionization constraints and explore their impact on reionization history.

Findings

Reionization duration ranges from 3.9 to 4.6 in redshift, longer than some observational limits.

Higher escape fraction slopes lead to earlier start and later end of reionization.

Simulations are consistent with galaxy observations but tension exists with some reionization duration constraints.

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.