Abstract

In this thesis, we present a new code SPHRAY to calculate the transfer of ionizing radiation through an arbitrary smoothed particle hydrodynamics density field. This represents a unique application in that it is the only particle based radiative transfer code with the speed to be applied to cosmological simulations with 512³ particles. In Chapter 2 we lay out the numerical algorithms the code is based on. In Chapter 3 we validate the results of our code on a set of standard radiative transfer tests that have been set in front of the community in the form of a comparison project. In Chapter 4 we describe an application of SPHRAY in calculating the neutral Hydrogen density field in the proximity zone of an accretion powered active galaxy. This scenario is especially well suited for our code in the sense that it requires the inclusion of shadowing effects, the treatment of a background as well as strong local sources, and the accurate calculation of very low neutral fractions. In Chapter 5 we present a large cosmological reionization application in which we explore the effect of smoothing the density field prior to doing radiative transfer as has been done in many previous works to lessen the computational cost.