A 3D Monte Carlo Photoionization Code for Modeling Diffuse Ionized Gas

We have developed a three dimensional Monte Carlo photoionization code tailored for the study of Galactic H II regions and the percolation of ionizing photons in diffuse ionized gas. We describe the code, our calculation of photoionization, heating & cooling, and the approximations we have employed for the low density H II regions we wish to study. Our code gives results in agreement with the Lexington H II region benchmarks. We show an example of a 2D shadowed region and point out the very significant effect that diffuse radiation produced by recombinations of helium has on the temperature within the shadow.