SCORCH I: The Galaxy-Halo Connection in the First Billion Years

SCORCH (Simulations and Constructions of the Reionization of Cosmic Hydrogen) is a new project to study the Epoch of Reionization (EoR). In this first paper, we probe the connection between observed high-redshift galaxies and simulated dark matter halos to better understand the primary source of ionizing radiation. High-resolution N-body simulations are run to quantify the abundance of dark matter halos as a function of mass M , accretion rate Ṁ , and redshift z. A new fit for the halo mass function dn/dM is ≈ 20% more accurate at the high-mass end. A novel approach is used to fit the halo accretion rate function dn/dṀ in terms of the halo mass function. Abundance matching against the observed galaxy luminosity function is used to estimate the luminosity-mass relation and the luminosity-accretion-rate relation. The inferred star formation efficiency is not monotonic with M nor Ṁ , but reaches a maximum value at a characteristic mass ∼ 2× 10 M⊙ and a characteristic accretion rate ∼ 6×102 M⊙yr at z ≈ 6. We find a universal EoR luminosity-accretion-rate relation and construct a fiducial model for the galaxy luminosity function. The Schechter parameters evolve such that φ⋆ decreases,M⋆ is fainter, and α is steeper at higher redshifts. We forecast for the upcoming James Webb Space Telescope and show that with apparent magnitude limit mAB ≈ 31 (32), it can observe & 11 (24) unlensed galaxies per square degree per unit redshift at least down to M⋆ at z . 13 (14).