Spitzer's Contribution to the AGN Population

Jennifer Donley, University of Arizona

While hard X-ray surveys are thought to provide the most complete and reliable AGN samples, such surveys can miss heavily obscured and Compton-thick AGN, significant numbers of which are predicted by models of the X-ray background. Therefore, many programs are using Spitzer-selected AGN candidates to supplement the X-ray results. We will critically review this IR population, discussing the following selection techniques: infrared power-law selection, infrared color-color selection, infrared/radio selection, and infrared/optical selection. After accounting for the reliability of these selection techniques, we find that the addition of Spitzer-selected AGN increases the number of known AGN by as much as ~50% in the deep X-ray fields.