A Census of Low Redshift AGNs

Active galactic nuclei (AGNs), powered by the infall of gas towards black holes, are extremely powerful celestial objects, but can be hidden from view and thus missed by astronomical surveys. In this thesis we have searched for AGNs with changing spectra and surveyed for AGNs using infrared light and optical spectroscopy. We have identified two previously unknown “changing look AGNs,” whose spectra have changed during the past twenty years. We have uncovered hundreds of obscured AGNs using infrared light, which would not have been readily identified by optical AGN surveys.