Program: GN-2008A-C-2

We propose a coordinated spectroscopic campaign to study a statistical sample of mid-infrared selected AGN. The targets are all from the Bo\"otes field, the target of {\em two} NOAO Survey Programs (NDWFS \& FLAMEX) as well as extensive additional data across the electromagnetic spectrum. Using {\it Spitzer}, we have demonstrated that mid-infrared observations provide an efficient and robust method to identify AGN. However, spectroscopy to date has predominantly focused on unobscured, or {\it type~1}, AGN, systematically avoiding obscured, or {\it type~2}, AGN which are expected to outnumber the type~1 population. Fundamental questions regarding type~2 AGN remain unanswered, beginning with issues as basic as their cosmic census. These issues are of looming importance as we strive to understand the interplay of AGN feedback in galaxy formation. This proposed program will provide spectroscopic data for nearly 100 obscured AGN, providing the largest such sample at cosmological redshifts. A matched spectroscopic sample of unobscured AGN in the same field is already in hand. Together, these data will conclusively address fundamental questions in AGN studies, beginning with the most basic issue of how the obscured AGN fraction depends on redshift and luminosity. {\em Our four-night classical Gemini run allocated in 2007A was almost entirely lost to a telescope failure.}