Active galactic nucleus pairs from the Sloan Digital Sky Survey. I. the frequency on 5-100kpc scales

Abstract

Galaxygalaxy 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 Z̄ ∼ 0.1 with line-of-sight velocity offsets Δν < 600 km s?1 and projected separations rp < 100 h70-1 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 70-1 kpc ≲ rp < 100 h70-1 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 study their AGN and host-galaxy star formation properties in a companion paper. © 2011. The American Astronomical Society. All rights reserved.