The end of cosmic reionization

NAISS 2023/3-4


NAISS Large Compute

Principal Investigator:

Garrelt Mellema


Stockholms universitet

Start Date:


End Date:


Primary Classification:

10305: Astronomy, Astrophysics and Cosmology




This project studies the era in the history of the Universe during which the first generations of stars and galaxies changed the state of the hydrogen in the intergalactic medium from cold and neutral to hot and ionized. This process, known as Cosmic Reionization, is not well understood and is one of the current frontiers of cosmological research to which large amounts of telescope time, for example with the new JWST, are dedicated. Moreover, recent observational studies hint at an extended late reionization, a scenario which has been less studied through simulations. In this project, we will be performing large scale three-dimensional cosmological radiative transfer simulations focused on the final stages of reionization. During these stages, the progress of reionization is mostly determined by the presence of small amounts of residual neutral hydrogen in the already reionized regions which reduces the amount of ionizing radiation available to reionize the remaining fully neutral regions. Previous simulations have either not considered this effect, or have considered it using very crude approximations. In this project, we will produce a series of simulations that study this effect using a physically motivated approximation, taking into account the frequency dependence of the absorption of ionising photons, establishing the impact of spatial and temporal variations in the absorptions and calibrating it against the latest observations from Quasar spectra. We will also establish what is the most efficient way to accurately implement the absorption by residual neutral hydrogen, the process which controlled how cosmic reionization came to completion. The simulation results will further be made freely available for studying other aspects of the reionization process.