Type 2 Active Galactic Nuclei with Double-Peaked [OIII] Lines. II.
  Single AGNs with Complex Narrow-Line Region Kinematics are More Common than
  Binary AGNs
  (Abridged) Approximately 1% of low redshift (z<0.3) optically-selected type 2
AGNs show a double-peaked [OIII] narrow emission line profile in their
spatially-integrated spectra. Such features are usually interpreted as due
either to kinematics, such as biconical outflows and/or disk rotation of the
narrow line region (NLR) around single black holes, or to the relative motion
of two distinct NLRs in a merging pair of AGNs. Here we report follow-up near
infrared (NIR) imaging and optical slit spectroscopy of 31 double-peaked [OIII]
type 2 AGNs drawn from the SDSS parent sample presented in Liu et al (2010).
These data reveal a mixture of origins for the double-peaked feature. Roughly
10% of our objects are best explained by binary AGNs at (projected) kpc-scale
separations, where two stellar components with spatially coincident NLRs are
seen. ~ 50% of our objects have [OIII] emission offset by a few kpc,
corresponding to the two velocity components seen in the SDSS spectra, but
there are no corresponding double stellar components seen in the NIR imaging.
For those objects with sufficiently high quality slit spectra, we see velocity
and/or velocity dispersion gradients in [OIII] emission, suggestive of the
kinematic signatures of a single NLR. The remaining ~40% of our objects are
ambiguous, and will need higher spatial resolution observations to distinguish
between the two scenarios. Our observations therefore favor the kinematics
scenario with a single AGN for the majority of these double-peaked [OIII] type
2 AGNs. We emphasize the importance of combining imaging and slit spectroscopy
in identifying kpc binary AGNs, i.e., in no cases does one of these alone allow
an unambiguous identification. We estimate that ~ 0.5-2.5% of the z<0.3 type 2
AGNs are kpc-scale binary AGNs of comparable luminosities, with a relative
orbital velocity >~150 km/s.
