Between the two regimes of dark and star-forming haloes, a narrow mass range exists within which haloes remain star-free, but contain a small, dense core of neutral gas.nThis gas produces fluorescent recombination line emission driven by the UV background, which is limb-brightened when seen in projection to yield a distinctive ring-shaped morphology.nUsing a specially-designed radiative transfer code, I determined the expected properties and abundance of these fluorescent rings, and found that their properties can provide constraints on the shape and amplitude of the UV background, the nature of dark matter, and the primordial abundance of helium.

I’m currently working on a series of cosmological simulations, utilising the EAGLE galaxy formation model.nThese simulations feature a mass resolution equalling the highest achieved in EAGLE, while enlarging the simulated volume by a factor of eight.nWith the addition of radiative transfer post-processing, these simulations will allow the dynamics and distribution of simulated neutral hydrogen absorption features at z∼2−3z∼2−3 to be explored in great detail.