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S. E. Ridgway (JHU), M. D. Lacy (SSC, Caltech), G. Canalizo (UC Riverside), A. Sajina, L. Storrie-Lombardi, A. Petric, L. Armus (SSC, Caltech)
Recent results have revealed that there is probably a very close link between the formation and evolution of the supermassive black hole population and that of the galaxy population. Therefore, determining the actual number densities and properties of the active black hole population, both in the form of unobscured, type-1 quasars, and obscured, type-2 quasars, over a wide range of epochs is vital to understanding even the basics of galaxy formation. Until recently, it has been very difficult to identify luminosity-matched samples of quasar 1s and 2s, but having such a matched sample (selected on similar, mostly isotropic properties) is essential to resolving basic questions about the relationship between the two types. The two quasar types may be related purely by orientation, or it has also been posited that the type-2 quasars may evolve to type-1s after the initial triggering merging event. If evolution plays a strong role in determining whether a quasar is type 1 or 2, we might expect enhanced star-formation activity in the host galaxies of the type 2 quasars. We have selected a sample of type-2 and type-1 quasars matched in their mid-infrared luminosity from the Spitzer First Look Survey by selecting on their mid-infrared dust emission properties (as measured by Spitzer IRAC photometry). This emission provides a distinctive signature of AGN activity but should not be affected by orientation or torus opening angle. We will present initial results from a Spitzer program to obtain infrared data for this sample. Our IRS spectra allow us to directly compare the infrared SEDs of these two classes of quasar. By comparing the PAH features in the two populations, we can compare star formation activity in the host galaxies. By comparing the shapes of the mid-infrared SEDs and the equivalent widths of the silicate feature at 10 microns we can compare the dust environments of the AGN. We thus expect to gain a much better understanding of the relationship between the type-1 and type-2 quasars when the data is fully analysed.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.