Type 2 AGNs with Double-Peaked [O III] Lines: Narrow Line Region
  Kinematics or Merging Supermassive Black Hole Pairs?
  We present a sample of 167 type 2 AGNs with double-peaked [O III] 4959,5007
narrow emission lines, selected from the Seventh Data Release of the Sloan
Digital Sky Survey. The double-peaked profiles can be well modeled by two
velocity components, blueshifted and redshifted from the systemic velocity.
Half of these objects have a more prominent redshifted component. In cases
where the H-beta emission line is strong, it also shows two velocity components
whose line-of-sight (LOS) velocity offsets are consistent with those of [O
III]. The relative LOS velocity offset between the two components is typically
a few hundred km/s, larger by a factor of ~ 1.5 than the line full width at
half maximum of each component. The offset correlates with the host stellar
velocity dispersion sigma*. The host galaxies of this sample show
systematically larger sigma*, stellar masses, and concentrations, and older
luminosity-weighted mean stellar ages than a regular type 2 AGN sample matched
in redshift, [O III] 5007 equivalent width and luminosity; they show no
significant difference in radio properties. These double-peaked features could
be due to narrow-line region kinematics, or binary black holes. The statistical
properties do not show strong preference for or against either scenario, and
spatially resolved optical imaging, spectroscopy, radio or X-ray followup are
needed to draw firm conclusions.
