Are the Narrow‐Line Regions in Active Galaxies Dusty and Radiation Pressure Dominated?

The remarkable similarity between emission spectra of narrow line regions(NLR) in Seyfert Galaxies has long presented a mystery. In photoionizationmodels, this similarity implies that the ionization parameter is nearly alwaysthe same, about U ~ 0.01. Here we present dusty, radiation-pressure dominatedphotoionization models that can provide natural physical insight into thisproblem. In these models, dust and the radiation pressure acting on it providethe controlling factor in moderating the density, excitation and surfacebrightness of photoionized NLR structures. Additionally, photoelectric heatingby the dust is important in determining the temperature structure of themodels. These models can also explain the coexistence of the low-,intermediate- and coronal ionization zones within a single self-consistentphysical structure. The radiation pressure acting on dust may also be capableof driving the fast (~3000 km/s) outflows such as are seen in the HSTobservations of NGC 1068.Comment: 23 pages, 8 figures, Accepted by Ap