Introducing the THESAN project: radiationmagnetohydrodynamic simulations of the epoch of reionization
Abstract
We introduce the THESAN project, a suite of large volume ($L_\mathrm{box} = 95.5 \, \mathrm{cMpc}$) radiationmagnetohydrodynamic simulations that simultaneously model the largescale statistical properties of the intergalactic medium during reionization and the resolved characteristics of the galaxies responsible for it. The flagship simulation has dark matter and baryonic mass resolutions of $3.1 \times 10^6\, {\rm M_\odot }$ and $5.8 \times 10^5\, {\rm M_\odot }$, respectively. The gravitational forces are softened on scales of 2.2 ckpc with the smallest cell sizes reaching 10 pc at z = 5.5, enabling predictions down to the atomic cooling limit. The simulations use an efficient radiation hydrodynamics solver (AREPORT) that precisely captures the interaction between ionizing photons and gas, coupled to welltested galaxy formation (IllustrisTNG) and dust models to accurately predict the properties of galaxies. Through a complementary set of medium resolution simulations we investigate the changes to reionization introduced by different assumptions for ionizing escape fractions, varying dark matter models, and numerical convergence. The fiducial simulation and model variations are calibrated to produce realistic reionization histories that match the observed evolution of the global neutral hydrogen fraction and electron scattering optical depth to reionization. They also match a wealth of highredshift observationally inferred data, including the stellartohalomass relation, galaxy stellar mass function, star formation rate density, and the massmetallicity relation, despite the galaxy formation model being mainly calibrated at z = 0. We demonstrate that different reionization models give rise to varied bubble size distributions that imprint unique signatures on the 21 cm emission, especially on the slope of the power spectrum at large spatial scales, enabling current and upcoming 21 cm experiments to accurately characterize the sources that dominate the ionizing photon budget.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 April 2022
 DOI:
 10.1093/mnras/stab3710
 arXiv:
 arXiv:2110.00584
 Bibcode:
 2022MNRAS.511.4005K
 Keywords:

 radiative transfer;
 methods: numerical;
 galaxies: highredshift;
 dark ages;
 reionization;
 first stars;
 Astrophysics  Astrophysics of Galaxies;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 MNRAS, in press. Please visit www.thesanproject.com for more details