Mass Function of Binary Massive Black Holes in Active Galactic Nuclei

Abstract

If the activity of active galactic nuclei (AGNs) is predominantly induced by major galaxy mergers, then a significant fraction of AGNs should harbor binary massive black holes in their centers. We study the mass function of binary massive black holes in nearby AGNs based on the observed AGN black-hole mass function and theory of evolution of binary massive black holes interacting with a massive circumbinary disk in the framework of coevolution of massive black holes and their host galaxies. The circumbinary disk is assumed to be steady, axisymmetric, geometrically thin, self-regulated, self-gravitating but non-fragmenting with a fraction of Eddington accretion rate, which is typically one tenth of Eddington value. The timescale of orbital decay is {then} estimated as ~10^8yr for equal mass black-hole, being independent of the black hole mass, semi-major axis, and viscosity parameter but dependent on the black-hole mass ratio, Eddington ratio, and mass-to-energy conversion efficiency. This makes it possible for any binary massive black holes to merge within a Hubble time by the binary-disk interaction. We find that (1.8+-0.6%) for the equal mass ratio and (1.6+-0.4%) for the one-tenth mass ratio of the total number of nearby AGNs have close binary massive black holes with orbital period less than ten years in their centers, detectable with on-going highly sensitive X-ray monitors such as Monitor of All-sky X-ray Image and/or Swift/Burst Alert Telescope. Assuming that all binary massive black holes have the equal mass ratio, about 20% of AGNs with black hole masses of 10^{6.5-7}M_sun has the close binaries and thus provides the best chance to detect them.

22 pages, 11 figures, accepted for publication in PASJ. The draft was significantly revised. The major differences from the previous version are as follows: (1)The circumbinary disk is assumed to be a steady, axisymmetric, geometrically thin, self-gravitating, self-regulated but non-fragmenting. (2)The stellar scattering process is taken account of in the merging process of binary black holes

References in corpus (11)

• The MAXI Mission on the ISS: Science and Instruments for Monitoring All Sky X-Ray Images
• Massive black hole binary mergers within sub-pc scale gas discs
• Rapid Formation of Supermassive Black Hole Binaries in Galaxy Mergers with Gas
• The Population of Viscosity- and Gravitational Wave-Driven Supermassive Black Hole Binaries Among Luminous AGN
• Supermassive black hole binaries in gaseous and stellar circumnuclear discs: orbital dynamics and gas accretion
• A Candidate Sub-Parsec Supermassive Binary Black Hole System
• Merging and Clustering of the Swift BAT AGN Sample
• Black hole mergers: can gas discs solve the `final parsec' problem?
• A supermassive binary black hole with triple disks
• Modeling of Emission Signatures of Massive Black Hole Binaries: I Methods
• An Electromagnetic Signature of Galactic Black Hole Binaries That Enter Their Gravitational-Wave Induced Inspiral

Cited by in corpus (9)

• Gas driven massive black hole binaries: signatures in the nHz gravitational wave background
• Super-massive binary black holes and emission lines in active galactic nuclei
• Astrophysics of Super-massive Black Hole Mergers
• Rapid Merger of Binary Primordial Black Holes: an Implication for GW150914
• Binary Black Hole Accretion Flows From a Misaligned Circumbinary Disk
• Gravitational wave diagnosis of a circumbinary disk
• Radiatively inefficient accretion flows induced by gravitational-wave emission before massive black hole coalescence
• Warped Circumbinary Disks in Active Galactic Nuclei
• Searching for supermassive black holes binaries within SRG/eROSITA-De I: Properties of the X-ray selected candidates