SDSS-IV MaNGA: Galaxy Pair Fraction and Correlated Active Galactic
  Nuclei
  We have identified 105 galaxy pairs at z ~ 0.04 with the MaNGA integral-field
spectroscopic data. The pairs have projected separations between 1 kpc and 30
kpc, and are selected to have radial velocity offsets less than 600 km/s and
stellar mass ratio between 0.1 and 1. The pair fraction increases with both the
physical size of the integral-field unit and the stellar mass, consistent with
theoretical expectations. We provide the best-fit analytical function of the
pair fraction and find that ~3% of M* galaxies are in close pairs. For both
isolated galaxies and paired galaxies, active galactic nuclei (AGN) are
selected using emission-line ratios and H_alpha equivalent widths measured
inside apertures at a fixed physical size. We find AGNs in ~24% of the paired
galaxies and binary AGNs in ~13% of the pairs. To account for the selection
biases in both the pair sample and the MaNGA sample, we compare the AGN
comoving volume densities with those expected from the mass- and
redshift-dependent AGN fractions. We find a strong (~5x) excess of binary AGNs
over random pairing and a mild (~20%) deficit of single AGNs. The binary AGN
excess increases from ~2x to ~6x as the projected separation decreases from
10-30 kpc to 1-10 kpc. Our results indicate that pairing of galaxies preserves
the AGN duty cycle in individual galaxies but increases the population of
binary AGNs through correlated activities. We suggest tidally-induced
galactic-scale shocks and AGN cross-ionization as two plausible channels to
produce low-luminosity narrow-line-selected binary AGNs.
