Why a Windy Torus?

TL;DR

This paper proposes a dusty wind model driven by magnetic and radiation forces to explain the obscuring torus in quasars, accounting for observed spectral features and infrared emission.

Contribution

It introduces a novel dusty wind model combining magneto-centrifugal launching and radiation pressure to explain quasar obscuration and infrared emission.

Findings

The model can explain the obscuring torus and IR emission in quasars.

Magnetic fields are essential for launching the dusty wind.

Radiation pressure shapes and accelerates the wind.

Abstract

Mass ejection in the form of winds or jets appears to be as fundamental to quasar activity as accretion, and can be directly observed in many objects with broadened and blue-shifted UV absorption features. A convincing argument for radiation pressure driving this ionized outflow can be made within the dust sublimation radius. Beyond, radiation pressure is even more important, as high energy photons from the central engine can now push on dust grains. This physics underlies the dusty-wind model for the putative obscuring torus. Specifically, the dusty wind in our model is first launched from the outer accretion disk as a magneto-centrifugal wind and then accelerated and shaped by radiation pressure from the central continuum. Such a wind can plausibly account for both the necessary obscuring medium to explain the ratio of broad-to-narrow-line objects and the mid-infrared emission commonly seen in quasar spectral energy distributions. A convincing demonstration that large-scale, organized magnetic fields are present in radio-quiet active galactic nuclei is now required to bolster the case for this paradigm.