Active Galactic Nucleus Pairs from the Sloan Digital Sky Survey. I. The Frequency on ~ 5-100 kpc Scales

TL;DR

This study systematically identifies and analyzes 1286 AGN pairs at z ~ 0.1 from SDSS data, revealing their frequency, morphological features, and properties, thus significantly expanding the known sample of such pairs on 5-100 kpc scales.

Contribution

It provides the first large, systematic catalog of AGN pairs on 5-100 kpc scales, enhancing understanding of galaxy interactions and SMBH activity.

Findings

AGN pair fraction is 3.6% among all SDSS AGNs at 0.02 < z < 0.16.

Approximately 30% of pairs show tidal features, increasing to over 80% for brightest nuclei.

The sample size exceeds previous studies by more than an order of magnitude.

Abstract

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.