A New Model for Computing Composite Spectra of Extragalactic Photodissociation Regions

We have begun construction of a model of the integrated emission from an ensemble of star forming clouds within a normal galaxy. This modeling effort is motivated by recent Infrared Space Observatory results (Malhotra et al. 2000) which show that photodissociation region emission in normal galaxies is dominated by gas with high number density and high UV fields. We use the computational results of 1-D PDR models (Kaufman, Wolfire, Hollenbach & Luhman 1999) combined with results for Galactic GMC cloud mass distributions (e.g. Williams & McKee 1997), along with several assumed star formation rates and stellar initial mass functions, in order to learn how these variables affect the observed infrared emission. These model results are useful for comparisons with archival ISO data, as well as for observations to be made with SOFIA and SIRTF. This work is partially supported by NASA grant NCC 2-5338 and an NSF-REU grant, both to San José State University.