Photoionization models of the diffuse ionized gas in galactic halos

Abstract

This Ph.D. thesis is dealing with the modeling of the Diffuse Ionized Gas (DIG) in our Milky Way and external edge-on galaxies. The ionizing sources of this gas are up to now not known, energy estimations favor photoionization. The present work investigates the significance of this process. The observed emission line ratios are thereby modeled with the photoionization code CLOUDY. The present thesis is taking into account the correct geometry of the observations in contrast to previous models. The results show unambiguously that the trends of the line ratios are reproducible with the models. The strength of an additional heating source, as is discussed in the literature, is strongly diminished. Therefore photoionization is indeed the main ionizing source of the DIG.