Simulating reionization in numerical cosmology

The incorporation of radiative transfer effects into cosmological hydrodyna mical simulations is essential for understanding how the intergalactic medi um (IGM) makes the transition from a neutral medium to one that is almost f ully ionized. Here, we present an approximate numerical method designed to study in a statistical sense, how a cosmological density field is ionized b y a set of discrete point sources. A diffuse background radiation field is also computed self-consistently in our procedure. The method requires relat ively few time steps and can be employed with simulations having high resol ution. We describe the details of the algorithm and provide a description o f how the method can be applied to the output from a pre-existing cosmologi cal simulation to study the systematic reionization of a particular ionic s pecies. As a first application, we compute the reionization of He II by qua sars in the range 3 less than or similar to z less than or similar to 6. (C ) 2001 Elsevier Science B.V. All rights reserved.