Dusty, Radiation Pressure–Dominated Photoionization. II. Multiwavelength Emission Line Diagnostics for Narrow‐Line Regions

Abstract

Seyfert narrow-line region (NLR) emission line ratios are remarkably uniform, displaying only ~0.5 dex variation between galaxies, and even less within an individual object. Previous photoionization and shock models of this region were unable to explain this observation without the introduction of arbitrary assumptions or additional parameters. Dusty, radiation pressure-dominated photoionization models provide a simple physical mechanism that can reproduce this spectral uniformity between different objects. In the first paper of this series, we described this model and its implementation in detail, as well as presenting grids of model emission lines and examining the model structures. Here we explore these models further, demonstrating their ability to reproduce the observed Seyfert line ratios on standard line diagnostic diagrams in both the optical and UV. We also investigate the effects that the variation of metallicity, density, and ionizing spectrum have upon both the new paradigm and the standard photoionization models used hitherto. Along with the standard diagnostic diagrams we provide several new diagnostic diagrams in the UV, optical, and IR. These new diagrams can provide further tests of the dusty, radiation pressure photoionization paradigm as well as being used as diagnostics of the metallicity, density, and ionizing spectrum of the emission line clouds.