Radio-Selected Binary Active Galactic Nuclei from the Very Large Array
  Stripe 82 Survey
  Galaxy mergers play an important role in the growth of galaxies and their
supermassive black holes. Simulations suggest that tidal interactions could
enhance black hole accretion, which can be tested by the fraction of binary
active galactic nuclei (AGNs) among galaxy mergers. But determining the
fraction requires a statistical sample of binaries. We have identified
kpc-scale binary AGNs directly from high-resolution radio imaging. Inside the
92 square deg covered by the high-resolution Very Large Array survey of the
Sloan Digital Sky Survey (SDSS) Stripe 82 field, we identified 22 grade A and
30 grade B candidates of binary radio AGNs with angular separations less than
5" (10 kpc at z = 0.1). Eight of the candidates have optical spectra for both
components from the SDSS spectroscopic surveys and our Keck program. Two grade
B candidates are projected pairs, but the remaining six candidates are all
compelling cases of binary AGNs based on either emission line ratios or the
excess in radio power compared to the H-alpha-traced star formation rate. Only
two of the six binaries were previously discovered by an optical spectroscopic
search. Based on these results, we estimate that ~60% of our binary candidates
would be confirmed once we obtain complete spectroscopic information. We
conclude that wide-area high-resolution radio surveys offer an efficient method
to identify large samples of binary AGNs. These radio-selected binary AGNs
complement binaries identified at other wavelengths and are useful for
understanding the triggering mechanisms of black hole accretion.
