Obscured and Unobscured Active Galactic Nuclei in the Spitzer Space Telescope First Look Survey

Selection of active galactic nuclei (AGNs) in the infrared facilitates the discovery of AGNs whose optical emission is extinguished by dust. In this paper, we use the Spitzer Space Telescope First Look Survey (FLS) to assess the fraction of AGNs with mid-infrared (MIR) luminosities that are comparable to quasars and that are missed in optical quasar surveys because of dust obscuration. We begin by using the Sloan Digital Sky Survey (SDSS) database to identify 54 quasars within the 4 deg^2 extragalactic FLS. These quasars occupy a distinct region in MIR color space by virtue of their strong, red continua. This has allowed us to define an MIR color criterion for selecting AGN candidates. About 2000 FLS objects…

• NS
  National Science Foundation
• UD
  U.S. Department of Energy
• NA
  National Aeronautics and Space Administration
• AP
  Alfred P. Sloan Foundation
• CI
  California Institute of Technology
• M
  Max-Planck-Gesellschaft
• JP
  Jet Propulsion Laboratory