Active galactic nuclei ghosts: A systematic search for faded nuclei
  Physical processes such as re-ignition, enhancement, and fading of active
galactic nuclei (AGN) are not entirely understood because the timeline of these
events is expected to last many years. However, it is well known that the
differences in the energy budget between AGN components, like the optical
ionizing region and the mid-infrared (MIR) dust echoes, can be interpreted as a
hint on AGN evolution. Here we present a catalog of 88 AGN candidates showing
hints on the fading and rising of their activity in the nearby Universe. We use
AGN scaling relations to select them from an initial sample of 877 candidates
using publicly available optical, X-ray, and MIR luminosities. We then use the
multi-wavelength information to discard sources contaminated with extranuclear
emission and those with an X-ray luminosity not well corrected for absorption.
We find that 96% of our candidates are fading sources. This result suggests a
scenario where the Universe had its peak of AGN activity somewhere in the past
and is dominated by a fading phase at the present time. Alternatively, the
fading phase is longer than the rising phase, which is consistent with galaxy
merger simulations. Around 50% of these fading candidates are associated with
merging or interacting systems. Finally, we also find the existence of jets in
~30% of these candidates and that the preferred AGN dust geometry is
torus-like, instead of wind-like. Our results are compatible with the fading of
nuclear activity, expected if they are in an inefficient state.
