Program: GN-2006A-Q-30

The unified model of active galactic nuclei (AGN), in which orientation-dependent obscuration accounts for the differences between active galaxies of types 1 and 2, predicts a 10 micron silicate absorption feature in type 2 objects and strong silicate emission from the torus in the type 1s. The silicate feature is indeed observed in absorption, albeit weakly, in many type 2 AGN, but until recently the corresponding emission feature had only been securely detected in a single type 1 Seyfert galaxy. This has posed a great problem for models attempting to explain and predict the IR emission from the dusty AGN torus. In recent months, silicate emission features have been found in Spitzer spectra of several type 1 AGN, mostly distant quasars, ostensibly in agreement with the predictions of the unified model. However, the feature properties tend to suggest warm, extended dust rather than hot dust at the inner edge of the torus itself. We therefore propose a Michelle mid-IR study of three nearby Seyfert 1 nuclei with the aim of finding the compact source predicted by the unified model, clarifying the extent of any diffuse emission, and detecting and spatially locating the silicate feature in emission. The goals of this proposal form a valuable complement to the Spitzer observations and can only be achieved using the spatial resolution afforded by the largest ground-based telescopes.