Finding binary active galactic nuclei by the centroid shift in imaging
  surveys
  The census of binary active galactic nuclei (AGNs) is important in order to
understand the merging history of galaxies and the triggering of AGNs. However,
there is still no efficient method for selecting the candidates of binary AGNs.
The non-synchronous variations of the two AGNs in one binary system will induce
the shift of the image centroid. Since the astrometric error is normally much
smaller than the angular resolution of telescopes, it is possible to detect
such shifts even in the unresolved system via multi-epoch observations. We
perform some simulations and find that hundreds of observations are required to
discover compact binary AGNs. This method is suitable for the future
large-scale surveys, e.g., the Large Synoptic Survey Telescope, and it might
lead to a large sample of binary AGNs with a 1-2 yr survey.
