Sweeping away the mysteries of dusty continuous winds in active galactic nuclei

Abstract

An integral part of the unified model for active galactic nuclei (AGNs) is an axisymmetric obscuring medium, which is commonly depicted as a torus of gas and dust surrounding the central engine. However, a robust, dynamical model of the torus is required in order to understand the fundamental physics of AGNs and interpret their observational signatures. Here, we explore self-similar, dusty disk winds, driven by both magnetocentrifugal forces and radiation pressure, as an explanation for the torus. Using these models, we make predictions of AGN infrared (IR) spectral energy distributions from 2 to 100 μm by varying parameters such as the viewing angle (from i = 0° to 90°), the base column density of the wind (from N H, 0 = 1023 to 10 25cm-2), the Eddington ratio (from L/L Edd = 0.01 to 0.1), the black hole mass (from M BH = 108 to 109 M ⊙), and the amount of power in the input spectrum emitted in the X-ray relative to that emitted in the UV/optical (from αox = 1.1 to 2.1). We find that models with N H, 0 = 1025cm-2, L/L Edd = 0.1, and M BH ≥ 108 M ⊙ are able to adequately approximate the general shape and amount of power expected in the IR as observed in a composite of optically luminous Sloan Digital Sky Survey quasars. The effect of varying the relative power coming out in X-rays relative to the UV is a change in the emission below 5 μm from the hottest dust grains; this arises from the differing contributions to heating and acceleration of UV and X-ray photons. We see mass outflows ranging from 1 to 4 M ⊙yr-1, terminal velocities ranging from 1900 to 8000kms-1, and kinetic luminosities ranging from 1 × 1042 to 8 × 10 43ergs-1. Further development of this model holds promise for using specific features of observed IR spectra in AGNs to infer fundamental physical parameters of the systems. © 2012. The American Astronomical Society. All rights reserved.