Spectroscopic Indication for a Centi-parsec Supermassive Black Hole Binary in the Galactic Center of NGC 5548

Abstract

As a natural consequence of cosmological hierarchical structure formation, sub-parsec supermassive black hole binaries (SMBHBs) should be common in galaxies but thus far have eluded spectroscopic identification. Based on four decades of optical spectroscopic monitoring, we report that the nucleus of NGC 5548, a nearby Seyfert galaxy long suspected to have experienced a major merger about one billion years ago, exhibits long-term variability with a period of 14 years in the optical continuum and broad Hbeta emission line. Remarkably, the double-peaked profile of Hbeta shows systematic velocity changes with a similar period. These pieces of observations plausibly indicate that a SMBHB resides in the center of NGC 5548. The complex, secular variations in the line profiles can be explained by orbital motion of a binary with equal mass and a semi-major axis of 22 light-days (corresponding to 18 milli-parsec). At a distance of 75 Mpc, NGC 5548 is one of the nearest sub-parsec SMBHB candidates that offers an ideal laboratory for gravitational wave detection.

21 pages, 14 figures, 4 tables; To appear in ApJ

References in corpus (80)

• Stellar population synthesis at the resolution of 2003
• Coevolution (Or Not) of Supermassive Black Holes and Host Galaxies
• Central Masses and Broad-Line Region Sizes of Active Galactic Nuclei. II. A Homogeneous Analysis of a Large Reverberation-Mapping Database
• Nuclear Activity in Nearby Galaxies
• Structure and Formation of Elliptical and Spheroidal Galaxies
• The Low-Luminosity End of the Radius-Luminosity Relationship for Active Galactic Nuclei
• Are the Variations in Quasar Optical Flux Driven by Thermal Fluctuations?
• Gravitational-wave sensitivity curves
• Discovery of a binary AGN in the ultraluminous infrared galaxy NGC 6240 using Chandra
• On Uncertainties in Cross-Correlation Lags and the Reality of Wavelength-Dependent Continuum Lags in Active Galactic Nuclei
• The Lick AGN Monitoring Project: Broad-Line Region Radii and Black Hole Masses from Reverberation Mapping of Hbeta
• A massive binary black-hole system in OJ287 and a test of general relativity
• Binary Black Hole Accretion From a Circumbinary Disk: Gas Dynamics Inside the Central Cavity
• A possible close supermassive black-hole binary in a quasar with optical periodicity
• Keplerian Motion of Broad-Line Region Gas as Evidence for Supermassive Black Holes in Active Galactic Nuclei
• Reverberation Mapping Measurements of Black Hole Masses in Six Local Seyfert Galaxies
• A systematic search for close supermassive black hole binaries in the Catalina Real-Time Transient Survey
• Space Telescope and Optical Reverberation Mapping Project. II. Swift and HST Reverberation Mapping of the Accretion Disk of NGC 5548
• The Evolution of Black Hole Mass and Spin in Active Galactic Nuclei
• Radio Continuum Survey of an Optically-Selected Sample of Nearby Seyfert Galaxies
• Massive Black Hole Binary Evolution
• Three Dimensional MHD Simulation of Circumbinary Accretion Disks: Disk Structures and Angular Momentum Transport
• The Lick AGN Monitoring Project: The MBH - sigma Relation For Reverberation-Mapped Active Galaxies
• Supermassive black holes with high accretion rates in active galactic nuclei: I. First results from a new reverberation mapping campaign
• A Large Systematic Search for Recoiling and Close Supermassive Binary Black Holes
• Reverberation Measurements of the Inner Radius of the Dust Torus in 17 Seyfert Galaxies
• Double-Peaked Low-Ionization Emission Lines in Active Galactic Nuclei
• Nuclear Luminosities and Radio Loudness of Seyfert Nuclei
• Steps Toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. XVI. A Thirteen-Year Study of Spectral Variability in NGC 5548
• Relativistic boost as the cause of periodicity in a massive black-hole binary candidate
• Anatomy of the AGN in NGC 5548: I. A global model for the broadband spectral energy distribution
• Space Telescope and Optical Reverberation Mapping Project. I. Ultraviolet Observations of the Seyfert 1 Galaxy NGC 5548 with the Cosmic Origins Spectrograph on Hubble Space Telescope
• The Black Hole Mass Scale of Classical and Pseudo Bulges in Active Galaxies
• The Lick AGN Monitoring Project 2011: Fe II Reverberation from the Outer Broad-Line Region
• Systematic Uncertainties in Black Hole Masses Determined from Single Epoch Spectra
• Evolution of the Nuclear Accretion Disk Emission in NGC 1097: Getting Closer to the Black Hole
• Identifying Supermassive Black Hole Binaries with Broad Emission Line Diagnosis
• The Size of the Narrow-Line Emitting Region in the Seyfert 1 Galaxy NGC 5548 from Emission-Line Variability
• Rejection of the Binary Broad-Line Region Interpretation of Double-Peaked Emission Lines in Three Active Galactic Nuclei
• Double-Peaked Broad Emission Lines in NGC 4450 and Other LINERs
• Characteristic Signatures in the Thermal Emission from Accreting Binary Black Holes
• Super-massive binary black holes and emission lines in active galactic nuclei
• Constraining sub-Parsec Binary Supermassive Black Holes in Quasars with Multi-Epoch Spectroscopy. I. The General Quasar Population
• The First Spectroscopically Resolved Sub-parsec Orbit of a Supermassive Binary Black Hole
• NGC 5548 in a Low-Luminosity State: Implications for the Broad-Line Region
• A Bayesian Approach to Estimate the Size and Structure of the Broad-line Region in Active Galactic Nuclei Using Reverberation Mapping Data
• Evidence For A Precessing Accretion Disk in the Nucleus of NGC 1097
• A Periodically Varying Luminous Quasar at z=2 from the Pan-STARRS1 Medium Deep Survey: A Candidate Supermassive Black Hole Binary in the Gravitational Wave-Driven Regime
• Constraining Sub-Parsec Binary Supermassive Black Holes in Quasars with Multi-Epoch Spectroscopy. II. The Population with Kinematically Offset Broad Balmer Emission Lines
• Anatomy of the AGN in NGC 5548: II. The Spatial, Temporal and Physical Nature of the Outflow from HST/COS Observations
• A supermassive binary black hole with triple disks
• Long-Term Profile Variability in Active Galactic Nuclei with Double-Peaked Balmer Emission Lines
• Modeling of Emission Signatures of Massive Black Hole Binaries: I Methods
• Dynamics of warped accretion discs
• A Revised Calibration of the Virial Mass Estimator for Black Holes in Active Galaxies Based on Single-epoch H$\beta$ Spectra
• On different types of instabilities in black hole accretion discs. Implications for X-ray binaries and AGN
• Alignment and Precession of a Black Hole with a Warped Accretion Disc
• A probable Milli-Parsec Supermassive Binary Black Hole in the Nearest Quasar Mrk 231
• Profile variability of the H-alpha and H-beta broad emission lines in NGC5548
• Radio-Selected Binary Active Galactic Nuclei from the Very Large Array Stripe 82 Survey
• A Bayesian Method for the Intercalibration of Spectra in Reverberation Mapping
• Structure and evolution of circumbinary disks around supermassive black hole (SMBH) binaries
• Measurement of an AGN Central Mass on Centiparsec Scales: Results of Long-Term Optical Monitoring of Arp 102B
• A reduced orbital period for the supermassive black hole binary candidate in the quasar PG 1302-102?
• Variability of Fe II Emission Features in the Seyfert 1 Galaxy NGC 5548
• Recurring flares from supermassive black hole binaries: implications for tidal disruption candidates and OJ 287
• On the Scatter in the Radius - Luminosity Relationship for Active Galactic Nuclei
• A Radial Velocity Test for Supermassive Black Hole Binaries as an Explanation for Broad, Double-Peaked Emission Lines in Active Galactic Nuclei
• Variability of the H-beta line profiles as an indicator of orbiting bright spots in accretion disks of quasars: a case study of 3C 390.3
• The thermal-viscous disk instability model in the AGN context
• Observational Evidence of Accretion Disk-Caused Jet Precession in Galactic Nuclei
• Accretion Disks Around Binary Black Holes: A Quasistationary Model
• Interpreting the Variability of Double-Peaked Emission Lines in Active Galactic Nuclei with Stochastically Perturbed Accretion Disk Models
• Using Multiwavelength Observations to Determine the Black Hole Mass and Accretion Rate in the Type 1 Seyfert Galaxy NGC 5548
• Self-gravitating warped discs around supermassive black holes
• Multiple periods in the variability of the supermassive black hole binary candidate quasar PG1302-102?
• Binary Black Hole Accretion Flows From a Misaligned Circumbinary Disk
• Line shifts and sub-pc super-massive binary black holes
• Alignments Of Black Holes With Their Warped Accretion Disks And Episodic Lifetimes Of Active Galactic Nuclei
• Evolution of Warped Accretion Disks in Active Galactic Nuclei. I. Roles of Feeding at the Outer Boundaries

Cited by in corpus (85)

• Black holes, gravitational waves and fundamental physics: a roadmap
• Exoplanetary Atmospheres: Key Insights, Challenges and Prospects
• The Quest for Dual and Binary Supermassive Black Holes: A Multi-Messenger View
• Electromagnetic Counterparts to Massive Black Hole Mergers
• The Gravitational-Wave Physics II: Progress
• Lijiang 2.4-meter Telescope and its Instruments
• Periodic self-lensing from accreting massive black hole binaries
• A Large Systematic Search for Close Supermassive Binary and Rapidly Recoiling Black Holes - III. Radial Velocity Variations
• Evidence for periodicity in 43 year-long monitoring of NGC 5548
• Constraining Sub-Parsec Binary Supermassive Black Holes in Quasars with Multi-Epoch Spectroscopy. III. Candidates from Continued Radial Velocity Tests
• Monitoring AGNs with Hβ Asymmetry. I. First Results: Velocity-resolved Reverberation Mapping
• Reverberation Mapping of the Broad-line Region in NGC 5548: Evidence for Radiation Pressure?
• Minidisks in Binary Black Hole Accretion
• How frequent are close supermassive binary black holes in powerful jet sources?
• A hidden friend for the galactic center black hole, Sgr A*
• Varstrometry for Off-nucleus and Dual sub-Kpc AGN (VODKA): Methodology and Initial Results with Gaia DR2
• Long-term optical spectral monitoring of a changing-look AGN NGC 3516 I: Continuum and broad-line flux variability
• Multi-messenger Time-domain Signatures Of Supermassive Black Hole Binaries
• A Possible ~20 yr Periodicity in Long-term Optical Photometric and Spectral Variations of the Nearby Radio-Quiet Active Galactic Nucleus Ark 120
• Partial dust obscuration in active galactic nuclei as a cause of broad-line profile and lag variability, and apparent accretion disc inhomogeneities
• Monitoring AGNs with H$\beta$ Asymmetry. III. Long-term Reverberation Mapping Results of 15 Palomar-Green Quasars
• Possible Quasi-Periodic modulation in the z = 1.1 $\gamma$-ray blazar PKS 0426-380
• The optical variability of Supermassive Black Hole Binary Candidate PG1302-102: Periodicity and perturbation in the light curve
• Radio-loudness along the quasar main sequence
• Emission Signatures from Sub-parsec Binary Supermassive Black Holes I: Diagnostic Power of Broad Emission Lines
• Unveiling sub-parsec supermassive black hole binary candidates in active galactic nuclei
• Toward the unambiguous identification of supermassive binary black holes through Bayesian inference
• Evidence for Two Distinct Broad-Line Regions from Reverberation Mapping of PG 0026+129
• Supermassive Black Hole and Broad-line Region in NGC~5548: Results from Five-season Reverberation Mapping
• Oscillatory patterns in the light curves of 5 long-term monitored type 1 AGN
• Joint constraints on cosmological parameters using future multi-band gravitational wave standard siren observations
• Emission Signatures from Sub-parsec Binary Supermassive Black Holes II: Effect of Accretion Disk Wind on Broad Emission Lines
• Kinematic signatures of reverberation mapping of close binaries of supermassive black holes in active galactic nuclei
• Lighthouse in the Dust: Infrared Echoes of Periodic Emission from Massive Black Hole Binaries
• The minimum and maximum gravitational-wave background from supermassive binary black holes
• Star cluster disruption by a massive black hole binary
• The intrinsic Baldwin effect in broad Balmer lines of six long-term monitored AGNs
• Systematic Redshift of the Fe III UV Lines in Quasars. Measuring Supermassive Black Hole Masses under the Gravitational Redshift Hypothesis
• Parsec-scale jet properties of the quasar PG 1302$-$102
• Constraining a companion of the galactic center black hole, Sgr A*
• Emission Signatures from Sub-parsec Binary Supermassive Black Holes III: Comparison of Models with Observations
• Kinematic signatures of reverberation mapping of close binaries of supermassive black holes in active galactic nuclei. II. Atlas of two-dimensional transfer functions
• Likelihood for Detection of Sub-parsec Supermassive Black Hole Binaries in Spectroscopic Surveys
• Dynamical evidence of the sub-parsec counter-rotating disc for a close binary of supermassive black holes in the nucleus of NGC 1068
• Long-term monitoring of the broad-line region properties in a selected sample of AGN
• Kinematic signatures of reverberation mapping of close binaries of supermassive black holes in active galactic nuclei III. The case of elliptical orbits
• Optical follow-up of the tick-tock massive black hole binary candidate
• On using inspiralling supermassive binary black holes in the PTA frequency band as standard sirens to constrain dark energy
• Variation of Broad Emission Lines from QSOs with Optical/UV Periodicity to Test the Interpretation of Supermassive Binary Black Holes
• Supermassive Binary Black Hole Evolution can be traced by a small SKA Pulsar Timing Array
• Variable classification in the LSST era: Exploring a model for quasi-periodic light curves
• On possible proxies of AGN light curves cadence selection in future time domain surveys
• Detecting subparsec super-massive binary black holes: Long termmonitoring perspective
• The SDSS-V Black Hole Mapper Reverberation Mapping Project: Unusual Broad-Line Variability in a Luminous Quasar
• Spiral Arms in Broad-line Regions of Active Galactic Nuclei. II. Loosely Wound Cases: Reverberation Properties
• Differential Interferometric Signatures of Close Binaries of Supermassive Black Holes in Active Galactic Nuclei
• Predicting the broad lines polarization emitted by supermassive binary black holes
• ESPRESSO reveals a single but perturbed broad-line region in the supermassive black hole binary candidate PG 1302-102
• Final stage of merging binaries of supermassive black holes: observational signatures
• Iterative time-domain method for resolving multiple gravitational wave sources in Pulsar Timing Array data
• Pulsar Timing Array Constraints on the Merger Timescale of Subparsec Supermassive Black Hole Binary Candidates
• Constraints on individual supermassive binary black holes using observations of PSR J1909-3744
• Varstrometry Selected Radio-Loud Candidates of Dual and Off-Nucleus Quasars at Sub-kpc Scales
• A fast test for the identification and confirmation of massive black hole binaries
• Testing Einstein's Equivalence Principle and its Cosmological Evolution from Quasar Gravitational Redshifts
• Differential Interferometric Signatures of Close Binaries of Supermassive Black Holes in Active Galactic Nuclei: II. Merged Broad Line Regions
• SALT long-slit spectroscopy of HE 0435-4312: fast displacement in the Mg II emission line
• Periodic optical variability of AGN
• Exploring possible relations between optical variability time scales and broad emission line shapes in AGN
• Very Large Array imaging rules out precessing radio jets in three DES$-$SDSS-selected candidate periodic quasars
• Detection of an Unidentified Soft X-ray Emission Feature in NGC 5548
• Strange Quasar Candidates with Abnormal Astrometric Characteristics from Gaia EDR3 and SDSS (SQUAB-II): Optical Identifications
• Detection of eccentric close-binary supermassive black holes with incomplete interferometric data
• A novel approach to study the variability of NGC 5548
• Ultra-low-frequency gravitational waves from individual supermassive black hole binaries as standard sirens
• On Variation of Light Curves and Broad Emission Lines for Periodic QSOs from co-rotating Supermassive binary black holes in elliptical orbits
• Time Evolution of Mg II in SDSS J2320+0024: Implications for a Subparsec Binary Supermassive Black Hole System
• Probing Boson Clouds with Supermassive Black Hole Binaries
• The broad emission line asymmetry in low mass ratio of supermassive binary black holes on elliptical orbits
• A Supermassive Binary Black Hole Candidate in Mrk 501
• Variations of Broad Emission Lines from periodicity QSOs under the interpretation of supermassive binary black holes with misaligned circumbinary broad line regions
• Search for Continuous Gravitational Wave Signals in Pulsar Timing Residuals: A New Scalable Approach with Diffusive Nested Sampling
• Searching for unresolved massive black hole pairs through AGN photometric variability
• Investigating the Accretion Nature of Binary Supermassive Black Hole Candidate SDSS J025214.67-002813.7
• Binary black hole signatures in polarized light curves