Thomas, A. DGroves, BrentSutherland, R. SDopita, M. A.Kewley, LisaJin, C.2017-03-292017-03-291538-4357http://hdl.handle.net/1885/114164We present a simplified model of active galactic nucleus (AGN) continuum emission designed for photoionization modeling. The new model OXAF reproduces the diversity of spectral shapes that arise in physically based models. We identify and explain degeneracies in the effects of AGN parameters on model spectral shapes, with a focus on the complete degeneracy between the black hole mass and AGN luminosity. Our reparametrized model OXAF removes these degeneracies and accepts three parameters that directly describe the output spectral shape: the energy of the peak of the accretion disk emission Epeak, the photon power-law index of the non-thermal emission Γ, and the proportion of the total flux that is emitted in the non-thermal component pNT. The parameter Epeak is presented as a function of the black hole mass, AGN luminosity, and “coronal radius” of the OPTXAGNF model upon which OXAF is based. We show that the soft X-ray excess does not significantly affect photoionization modeling predictions of strong emission lines in Seyfert narrow-line regions. Despite its simplicity, OXAF accounts for opacity effects where the accretion disk is ionized because it inherits the “color correction” of OPTXAGNF. We use a grid of MAPPINGS photoionization models with OXAF ionizing spectra to demonstrate how predicted emission-line ratios on standard optical diagnostic diagrams are sensitive to each of the three OXAF parameters. The OXAF code is publicly available in the Astrophysics Source Code Library.B.G. gratefully acknowledges the support of the Australian Research Council as the recipient of a Future Fellowship (FT140101202). L.K. and M.D. acknowledge support from ARC discovery project #DP160103631. C.J. acknowledges the support by the Bundesministerium für Wirtschaft und Technologie/Deutsches Zentrum für Luft- und Raumfahrt (BMWI/DLR, FKZ 50 OR 1604) and the Max Planck Society. We are grateful to both Chris Done, who received an early draft of this paper, and the anonymous referee for helpful comments.application/pdf© 2016. The American Astronomical Society. http://www.sherpa.ac.uk/romeo/issn/0004-637X/..."Publisher's version/PDF may be used on any website or authors' institutional repository" from SHERPA/RoMEO site (as at 29/03/17).black hole physicsgalaxies: individual (NGC 1365)ISM: lines and bandsline: formationquasars: emission lines201610.3847/1538-4357/833/2/266