3D transfer of the diffuse ionizing radiation in ISM flows and the preionization of a Herbig-Haro working surface

We have developed a new 3D radiation-gasdynamic code which includes a treat ment of the transfer of the diffuse ionizing radiation produced by the flow . We describe this code in some detail, and then apply it to the problem of preionization in the working surface of a Herbig-Haro (HH) jet. This 3D numerical simulation shows the spatial structure of the precursor o f a working surface of a HH jet. As has been previously described in the co ntext of plane-parallel shocks, the diffuse radiation both ionizes and heat s the preshock flow. We find that the diffuse, ionizing radiation also sign ificantly affects the post-shock flow stratification and the location of th e shocks in the simulations, likely leading to different predicted spectra for models with or without diffuse radiation. Synthetic H alpha emission-li ne maps produced from our simulations show that the preionized region will be difficult to observe due to its faintness compared to the post-bow shock emitting region.