TYPE 2 ACTIVE GALACTIC NUCLEI WITH DOUBLE-PEAKED [O III] LINES: NARROW- LINE REGION KINEMATICS OR MERGING SUPERMASSIVE BLACK HOLE PAIRS?

We present a sample of 167 type 2 active galactic nuclei (AGNs) with double-peaked [O III]lambda lambda 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(-1), larger by a factor of similar to 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(s)*, stellarmasses, and concentrations, and older luminosity-weighted mean stellar ages than a regular type 2 AGN sample matched in redshift, [O III] lambda 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 follow-up are needed to draw firm conclusions.