Program: GS-2005A-Q-50

Dust obscuration is the primary reason that we cannot see the broad line region in Seyfert 2 galaxies. That most luminous Seyfert 2s do have hidden broad line regions is clear from existing spectropolarimetry, and that dust is the reason we cannot see this broad lie region is equally evident from hard x-ray spectroscopy. By contrast Seyfert 1s show little if any obscuration. In this sense orientation dependent unification for the different classes of Seyfert galaxies is clearly successful. Depsite this, there are several key problems with the unified model. The subject of this proposal regards the nature of the obscuring dust itself. We naively expect the typically highly obscured Seyfert 2s to show optically thick dust emission, and hence strong absorption in the 9.7 micron silicate feature. By contrast we would expect the optically thin emission in Seyert 1s to give rise to silicate emission. Neither of these are unambiguously true. Most Seyfert 1s show flat featureless 10 micron spectra, and some highly obscured Seyfert 2s show very little absorption. In addition, we have shown that the observed 25micron luminosity of Seyfert galaxies is a remarkably good indicator of the underlying AGN luminosity, seemingly regardless of the level of obscuraton present. More recent models may help to explain this behaviour but have never been tested fully. By obtaining mid IR imaging and spectroscopy of a relatively nearby sample of AGN spanning a range of luminosty and obscuration we can test these models fully, and hence increase out understanding considerably of orientation dependent unification in AGN.