A High Fraction of Double-peaked Narrow Emission Lines in Powerful
  Active Galactic Nuclei
  One percent of redshift z~0.1 Active Galactic Nuclei (AGNs) show velocity
splitting of a few hundred km/s in the narrow emission lines in spatially
integrated spectra. Such line profiles have been found to arise from the bulk
motion of ionized gas clouds associated with galactic-scale outflows, merging
pairs of galaxies each harboring a supermassive black hole (SMBH), and/or
galactic-scale disk rotation. It remains unclear, however, how the frequency of
narrow-line velocity splitting may depend on AGN luminosity. Here we study the
correlation between the fraction of Type 2 AGNs with double-peaked narrow
emission lines and AGN luminosity as indicated by [O III]5007 emission-line
luminosity L_[O III]. We combine the sample of Liu et al. (2010) at z~0.1 with
a new sample of 178 Type 2 AGNs with double-peaked [O III] emission lines at
z~0.5. We select the new sample from a parent sample of 2089 Type 2 AGNs from
the SDSS-III/Baryon Oscillation Spectroscopic Survey. We find a statistically
significant (~4.2\sigma) correlation between L_[O III] and the fraction of
objects that exhibit double-peaked narrow emission lines among all Type 2 AGNs,
corrected for selection bias and incompleteness due to [O III] line width,
equivalent width, splitting velocity, and/or equivalent width ratio between the
two velocity components. Our result suggests that galactic-scale outflows
and/or merging pairs of SMBHs are more prevalent in more powerful AGNs,
although spatially resolved follow up observations are needed to resolve the
origin(s) for the narrow-line velocity splitting for individual AGNs.
