Numerical Simulations of Fe <scp>ii</scp> Emission Spectra

Abstract

This paper describes the techniques that we have used to incorporate a large-scale model of the Feì on and resulting Fe II emission into CLOUDY, a spectral synthesis code designed to simulate conditions within a plasma and model the resulting spectrum.We describe the numerical methods we use to determine the level populations, mutual line overlap Ñuorescence, collisional e †ects, and the heatingcooling e †ects of the atom on its environment.As currently implemented, the atom includes the lowest 371 levels (up to 11.6 eV) and predicts intensities of 68,635 lines.We describe our data sources, which include the most recent transition probabilities and collision strengths.Although we use detailed Ðts to temperature-dependent collision strengths where possible, in many cases the uncertain approximation g6 is the only source for collision data.The atom is designed to be readily expanded to include more levels and to incorporate more accurate sets of collision and radiative data as computers grow faster and the atomic databases expand.We present several test cases showing that the atom goes to LTE in the limits of high particle and radiation densities.We give an overview of general features of the Fe II spectra as their dependencies on the basic parameters of our models (density, Ñux, microturbulent velocity, the Fe abundance, and Lya pumping).Finally, we discuss several applications to active galactic nuclei to illustrate the diagnostic power of the Fe II spectrum and make some predictions for UV observations.