Abel, N. ; Ferland, G. ; Shaw, G. ; van Hoof, P. A.

published in Bulletin of the American Astronomical Society, 38, pp. 49.21 (2006)

Abstract: UltraLuninous Infrared Galaxies (ULIRGs) may hold the key to understanding two important astrophysical phenomena; the galactic merger environment in which a significant fraction of the stars in the universe likely formed and the evolutionary connection between galaxy mergers and active galactic nuclei (AGN). Since ULIRGs emit the bulk of their energy in the IR, infrared observations must lead the way in probing the physical conditions of these objects. Because ULIRG observations consist of ensembles of ionized, atomic, and molecular gas along with dust, theoretical calculations must be able to consider the effects of each phase to reproduce the observations and infer physical conditions. In this work, we use the spectral synthesis code Cloudy to calculate the spectrum of a cloud illuminated by a central AGN/starburst continuum. We explore how important spectral diagnostics, such as the [CII]/FIR ratio, varies with ionization parameter and extinction. We also attempt to reproduce the correlation between PAH and O IV/Ne II emission, an important diagnostic in determining the relative contribution of AGN and starburst activity in ULIRGs. Overall, our computational methods offer a powerful tool for interpreting spectra from current and future infrared missions.

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