Photoionization of Disk Winds

Abstract

The disk-wind model suggests that the broad emission lines of a quasar are emitted from the surface of the accretion disk feeding the central black hole. In this paper, we assume that a line-driven wind emerges from the illuminated face of the disk and calculate the line emission produced by this wind. The location and mass-loss rate of the wind are determined by the physics of the line driving. We calculate line ratios and the radius at which each line forms using a photoionization code. From the source functions, together with simple wind-radiative transfer calculations, we then calculate line profiles. The model reproduces the observed line ratios with a degree of success comparable to standard cloud models, underpredicting the flux in low-ionization lines and in N V λ1240. Using C IV to fix all the model parameters except for the line ratios, we find that the model successfully predicts the variety of line profiles seen in two PG quasars. We also present line profiles for Ne VIII that are very broad (FWHM ~ 17,000 km s-1) and predict that Mg X, while unlikely to be seen in emission, will be seen in absorption (in broad absorption line quasars). As suggested by previous authors, we find that the very broad feature seen around λ2800 and usually attributed to Mg II is actually a blend of that line, which is relatively narrow, and Fe II emission.