Simulating the neutral hydrogen distribution during cosmic reionization

• Main Author: Hassan, Sultan
• Other Authors: Dave, Romeel
• Language: en
• Published: University of the Western Cape 2018
• Online Access: http://hdl.handle.net/11394/5963

Philosophiae Doctor - PhD (Physics) === We improve on the physical treatment of ionising source and sink populations in the large scale semi-numerical simulations by implementing new physically motivated parametrizations taken from high-resolution radiative transfer simulations, in order to account for the non-linear dependence on halo mass, redshift and environment. This provides an efficient unique way to connect the small scale astrophysics to the large scale cosmology. These new parametrizations allow the model to simultaneously match all current reionization observations with only 4% photon escape fraction. These improvements result in 2-3 x 21cm power spectrum variations on small and large scales, and hence showing the importance of accurately treating ionising sources and sinks in 21cm simulations. We further implement time-integrated effects to accurately track the evolution of ionising photons, inhomogeneous recombinations and partially ionized regions during reionization. Including these effects yields larger HII regions and a more sudden reionization, which leads to an order of magnitude more 21cm power on large scales. We develop a robust parameter estimation pipeline to constrain the model astrophysical parametersagainst several reionization observations. We find that future 21cm observations provide tighter constraints on the astrophysical parameters and complement different derived constraints from other reionization observations. We finally employ the high redshift observations to add ionising photons from Active Galactic Nuclei (AGN), in order to assess the ability of AGN-dominated models to solely complete reionization. Unlike the case with galaxies, the AGN-only models cannot simultaneously match all current reionization observations. AGN-only models produce 21cm power spectrum that is 2 x higher on all scales as compared with galaxies-dominated models. Future 21cm surveys will play a key role to distinguishing between these two scenarios, even though AGN are highly unlikely to drive cosmic reionization.