Lyman-alpha pumping during the dark ages

This project uses Ly𝛼 radiative-transfer simulations of galaxies and their environments to quantify Wouthuysen–Field coupling and derive sub-grid prescriptions for large-scale 21 cm/EoR simulations. The aim is to bridge the vast scale gap—from sub-pc Ly𝛼 scattering to Mpc-scale reionization structures—so upcoming 21 cm experiments can model this effect accurately.

The next generation of telescopes such as the SKA target the 21cm spinflip transition line of neutral hydrogen to map out the Epoch of Reionization (EoR). Ly𝛼 scattering changes the state of hydrogen and thus affects the 21cm signal through the so-called Wouthuysen–Field effect. While this effect is known since a long time, models studying it are very rudimentary. This is because the range of scales (≪pc mean free path of Ly𝛼 photons to >Mpc coherent regions in the EoR) is simply too large to model the effect correctly. In this project, you will run Ly𝛼 radiative transfer simulations of models of galaxies and their surroundings, record the scattering rates and try to find prescriptions to model this effect correctly in larger scale EoR simulations where the gas and radiative transfer around galaxies cannot properly be resolved.