Active Galactic Nucleus Pairs from the Sloan Digital Sky Survey. I. The
  Frequency on ~ 5-100 kpc Scales
  Galaxy-galaxy mergers and close interactions have long been regarded as a
viable mechanism for channeling gas toward the central supermassive black holes
(SMBHs) of galaxies which are triggered as active galactic nuclei (AGNs). AGN
pairs, in which the central SMBHs of a galaxy merger are both active, are
expected to be common from such events. We conduct a systematic study of 1286
AGN pairs at z ~ 0.1 with line-of-sight velocity offsets dv < 600 km/s and
projected separations r_p < 100 kpc, selected from the Seventh Data Release of
the Sloan Digital Sky Survey (SDSS). This AGN pair sample was drawn from
138,070 AGNs optically identified based on diagnostic emission line ratios
and/or line widths. The fraction of AGN pairs with 5 kpc ~< r_p < 100 kpc among
all spectroscopically selected AGNs at 0.02 < z < 0.16 is 3.6% after correcting
for SDSS spectroscopic incompleteness; ~ 30% of these pairs show morphological
tidal features in their SDSS images, and the fraction becomes >~ 80% for pairs
with the brightest nuclei. Our sample increases the number of known AGN pairs
on these scales by more than an order of magnitude. We present their AGN and
host-galaxy star formation properties in a companion paper.
