AGN pairs: chance superpositions or black hole binaries?

Abstract

Several active galactic nuclei (AGN) with multiple sets of emission lines separated by over 2000 km/s have been observed recently. These have been interpreted as being due to massive black hole (MBH) recoil following a black hole merger, MBH binaries, or chance superpositions of AGN in galaxy clusters. Moreover, a number of double-peaked AGN with velocity offsets of ~ a few 100 km/s have also been detected and interpreted as being due to the internal kinematics of the narrow line regions or MBH binary systems. Here we reexamine the superposition model. Using the Millennium Run we estimate the total number of detectable AGN pairs as a function of the emission line offset. We show that AGN pairs with high velocity line separations up to ~2000 km/s are very likely to be chance superpositions of two AGN in clusters of galaxies for reasonable assumptions about the relative fraction of AGN. No superimposed AGN pairs are predicted for velocity offsets in excess of ~3000 km/s as the required AGN fractions would violate observational constraints. The high velocity AGN pair numbers predicted here are competitive with those predicted from the models relying on MBH recoil or MBH binaries. However, the model fails to account for the largest emission line velocity offsets that require the presence of MBH binaries.

4 pages, 2 figures, submitted to ApJ Letters

References in corpus (17)

• The hierarchical formation of the brightest cluster galaxies
• Large Merger Recoils and Spin Flips From Generic Black-Hole Binaries
• A Candidate Sub-Parsec Supermassive Binary Black Hole System
• A Search for Binary Active Galactic Nuclei: Double-Peaked [OIII] AGN in the Sloan Digital Sky Survey
• Type 2 AGNs with Double-Peaked [O III] Lines: Narrow Line Region Kinematics or Merging Supermassive Black Hole Pairs?
• Active Galactic Nuclei with Double-peaked Narrow Lines: Are They Dual AGNs?
• Radial Velocity Offsets Due to Mass Outflows and Extinction in Active Galactic Nuclei
• Clustering Analyses of 300,000 Photometrically Classified Quasars--II. The Excess on Very Small Scales
• Quasar Clustering at $25\kpch$ from a Complete Sample of Binaries
• Long-Term Profile Variability of Double Peaked Emission Lines in Active Galactic Nuclei
• Narrow double-peaked emission lines of SDSS J131642.90+175332.5: signature of a single or a binary AGN in a merger, jet-cloud interaction, or unusual narrow-line region geometry
• The Quasar SDSS J105041.35+345631.3: Black Hole Recoil or Extreme Double-Peaked Emitter?
• HST Images and KPNO Spectroscopy of the Binary Black Hole Candidate SDSS J153636.22+044127.0
• Discovery of Radio Emission from the Quasar SDSS J1536+0441, a Candidate Binary Black-Hole System
• Probing the nature of the massive black hole binary candidate SDSS J1536+0441
• A photometric study of the field around the candidate recoiling/binary black hole SDSS J092712.65+294344.0
• Recoiling Supermassive Black Holes in Spin-flip Radio Galaxies

Cited by in corpus (10)

• What Drives the Growth of Black Holes?
• A systematic search for massive black hole binaries in SDSS spectroscopic sample
• Super-massive binary black holes and emission lines in active galactic nuclei
• Electromagnetic Counterparts to Black Hole Mergers
• Astrophysics of Super-massive Black Hole Mergers
• A Candidate Dual AGN at z=1.175
• The peculiar optical spectrum of 4C+22.25: Imprint of a massive black hole binary?
• New insights on the recoiling/binary black hole candidate J0927+2943 via molecular gas observations
• The quasar SDSS J142507.32+323137.4 : dual AGNs?
• Searching for unresolved massive black hole pairs through AGN photometric variability