Active Galactic Nuclei with Double-peaked Narrow Lines: Are They Dual
  AGNs?
  Double-peaked [O III]5007, profiles in active galactic nuclei (AGNs) may
provide evidence for the existence of dual AGNs, but a good diagnostic for
selecting them is currently lacking. Starting from $\sim$ 7000 active galaxies
in SDSS DR7, we assemble a sample of 87 type 2 AGNs with double-peaked [O
III]5007, profiles. The nuclear obscuration in the type 2 AGNs allows us to
determine redshifts of host galaxies through stellar absorption lines. We
typically find that one peak is redshifted and another is blueshifted relative
to the host galaxy. We find a strong correlation between the ratios of the
shifts and the double peak fluxes. The correlation can be naturally explained
by the Keplerian relation predicted by models of co-rotating dual AGNs. The
current sample statistically favors that most of the [O III] double-peaked
sources are dual AGNs and disfavors other explanations, such as rotating disk
and outflows. These dual AGNs have a separation distance at $\sim 1$ kpc scale,
showing an intermediate phase of merging systems. The appearance of dual AGNs
is about $\sim 10^{-2}$, impacting on the current observational deficit of
binary supermassive black holes with a probability of $\sim 10^{-4}$ (Boroson &
Lauer).
