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

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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 abundance and evolution of 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 M, and redshift z. A new fit for the halo mass function dn/dM is ≈ 20% more accurate at the high-mass end where bright galaxies are expected to reside. A novel approach is used to fit the halo accretion rate function dn/dM 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 M, but reaches a maximum value at a characteristic mass 2 × 10¹¹M and a characteristic accretion rate 6 × 10²M/ 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 more positive (fainter), and α is more negative (steeper) at higher redshifts. We forecast for the upcoming James Webb Space Telescope and show that with apparent magnitude limit m AB ≈ 31(32), it can observe 11(24) unlensed galaxies per square degree per unit redshift at least down to M⋆ at z 13(14).