The Aurora radiation-hydrodynamical simulations of reionization: calibration and first results

TL;DR

The Aurora simulations are a new set of radiation-hydrodynamical galaxy formation models that accurately capture small-scale gas structures, are calibrated to match observed star formation and reionization redshifts, and provide insights into early galaxy metallicities and IGM properties.

Contribution

We introduce the Aurora suite of radiation-hydrodynamical simulations with adaptive radiative transfer, calibrated to observations, and analyze their initial results on galaxy metallicities and IGM ionization.

Findings

Low-mass galaxy metallicities at z=6 match Local Group dwarf galaxies.

Reionization occurs at z=8.3, consistent with observations.

Higher resolution leads to lower photoionization rates and more neutral hydrogen absorbers.

Abstract

We introduce a new suite of radiation-hydrodynamical simulations of galaxy formation and reionization called Aurora. The Aurora simulations make use of a spatially adaptive radiative transfer technique that lets us accurately capture the small-scale structure in the gas at the resolution of the hydrodynamics, in cosmological volumes. In addition to ionizing radiation, Aurora includes galactic winds driven by star formation and the enrichment of the universe with metals synthesized in the stars. Our reference simulation uses 2x512^3 dark matter and gas particles in a box of size 25 comoving Mpc/h with a force softening scale of at most 0.28 kpc/h. It is accompanied by simulations in larger and smaller boxes and at higher and lower resolution, employing up to 2x1024^3 particles, to investigate numerical convergence. All simulations are calibrated to yield simulated star formation rate (SFR) functions in close agreement with observational constraints at redshift z = 7 and to achieve reionization at z = 8.3, which is consistent with the observed optical depth to reionization. We focus on the design and calibration of the simulations and present some first results. The median stellar metallicities of low-mass galaxies at z = 6 are consistent with the metallicities of dwarf galaxies in the Local Group, which are believed to have formed most of their stars at high redshifts. After reionization, the mean photoionization rate decreases systematically with increasing resolution. This coincides with a systematic increase in the abundance of neutral hydrogen absorbers in the IGM.