A Search for Binary Active Galactic Nuclei: Double-Peaked [OIII] AGN in
  the Sloan Digital Sky Survey
  We present AGN from the Sloan Digital Sky Survey (SDSS) having double-peaked
profiles of [OIII] 5007,4959 and other narrow emission-lines, motivated by the
prospect of finding candidate binary AGN. These objects were identified by
means of a visual examination of 21,592 quasars at z < 0.7 in SDSS Data Release
7 (DR7). Of the spectra with adequate signal-to-noise, 148 spectra exhibit a
double-peaked [OIII] profile. Of these, 86 are Type 1 AGN and 62 are Type 2
AGN. Only two give the appearance of possibly being optically resolved double
AGN in the SDSS images, but many show close companions or signs of recent
interaction. Radio-detected quasars are three times more likely to exhibit a
double-peaked [OIII] profile than quasars with no detected radio flux,
suggesting a role for jet interactions in producing the double-peaked profiles.
Of the 66 broad line (Type 1) AGN that are undetected in the FIRST survey, 0.9%
show double peaked [OIII] profiles. We discuss statistical tests of the nature
of the double-peaked objects. Further study is needed to determine which of
them are binary AGN rather than disturbed narrow line regions, and how many
additional binaries may remain undetected because of insufficient line-of-sight
velocity splitting. Previous studies indicate that 0.1% of SDSS quasars are
spatially resolved binaries, with typical spacings of ~10 to 100 kpc. If a
substantial fraction of the double-peaked objects are indeed binaries, then our
results imply that binaries occur more frequently at smaller separations (< 10
kpc). This suggests that simultaneous fueling of both black holes is more
common as the binary orbit decays through these spacings.
