Measuring obscuration and reprocessing of AGN emission

The intrinsic emission of obscured active galactic nuclei (AGN) cannot be measured directly, but the obscured examples uniquely allow determination of the physical conditions near the central engine on 10-100 pc scales. The reprocessed radiation that emerges at X-ray and infrared energies, in particular, reveals the distribution of the obscuring medium. In general, X-ray spectroscopy shows the total column density along the line of sight, and in extremely obscured (Compton thick) cases, the fluorescent iron K alpha emission line is sensitive to viewing angle and covering fraction. Observed near- and mid-infrared spectra require an inhomogeneous distribution of material around the AGN, and they specifically depend on parameters such as the optical depth per obscuring cloud and the number of clouds along the line of sight. The total spatial extent of the obscuring region determines the shape of the far-infrared spectrum.