Gas Clumping in Self-Consistent Reionisation Models

Understand

We use a suite of cosmological hydrodynamic simulations including a self-consistent treatment for inhomogeneous reionisation to study the impact of galactic outflows and photoionisation heating on the volume-averaged recombination rate of the intergalactic medium (IGM).

• By incorporating an evolving ionising escape fraction and a treatment for self-shielding within Lyman limit systems, we have run the first simulations of "photon-starved" reionisation scenarios that simultaneously reproduce observations of the abundance of galaxies, the optical depth to electron scattering of cosmic microwave background photons \tau, and the effective optical depth to Lyman\alpha absorption at z=5.
• We confirm that an ionising background reduces the clumping factor C by more than 50% by smoothing moderately-overdense (\Delta=1--100) regions.
• Meanwhile, outflows increase clumping only modestly.