THE FIRST SPECTROSCOPICALLY RESOLVED SUB-PARSEC ORBIT OF A SUPERMASSIVE BINARY BLACK HOLE

One of the most intriguing scenarios proposed to explain how active galactic nuclei are triggered involves the existence of a supermassive binary black hole (BH) system in their cores. Here, we present an observational evidence for the first spectroscopically resolved sub-parsec orbit of a such system in the core of Seyfert galaxy NGC 4151. Using a method similar to those typically used for spectroscopic binary stars, we obtained radial velocity curves of the supermassive binary system, from which we calculated orbital elements and made estimates about the masses of the components. Our analysis shows that periodic variations in the light and radial velocity curves can be accounted for by an eccentric, sub-parsec Keplerian orbit with a 15.9 year period. The flux maximum in the light curve corresponds to the approaching phase of the secondary component toward the observer. According to the obtained results, we speculate that the periodic variations in the observed Hα line shape and flux are due to shock waves generated by the supersonic motion of the components through the surrounding medium. Given the large observational effort needed to reveal this spectroscopically resolved binary orbital motion, we suggest that many such systems may exist in similar objects even if they are hard to find. Detecting more of them will provide us with insight into the BH mass growth process.

[1]  Granada,et al.  Detailed characterization of Hβ emission line profile in low‐z SDSS quasars , 2009, 0912.4306.

[2]  M. Eracleous,et al.  LONG-TERM PROFILE VARIABILITY IN ACTIVE GALACTIC NUCLEUS WITH DOUBLE-PEAKED BALMER EMISSION LINES , 2010, 1003.5700.

[3]  L. Carrasco,et al.  Long-term variability of the optical spectra of NGC 4151. I. Light curves and flux correlations , 2008, 0804.0910.

[4]  Space Telescope Imaging Spectrograph Echelle Observations of the Seyfert Galaxy NGC 4151: Physical Conditions in the Ultraviolet Absorbers* , 2001, astro-ph/0101037.

[5]  Yue Shen,et al.  IDENTIFYING SUPERMASSIVE BLACK HOLE BINARIES WITH BROAD EMISSION LINE DIAGNOSIS , 2009, 0912.0541.

[6]  J. Katz,et al.  A Precessing Disk in OJ 287? , 1997 .

[7]  H. Schmitt,et al.  Probing the Ionization Structure of the Narrow-Line Region in the Seyfert 1 Galaxy NGC 4151 , 2008, 0802.3353.

[8]  L. Mayer,et al.  Direct formation of supermassive black holes via multi-scale gas inflows in galaxy mergers , 2009, Nature.

[9]  J. Krolik,et al.  THREE-DIMENSIONAL MAGNETOHYDRODYNAMIC SIMULATIONS OF CIRCUMBINARY ACCRETION DISKS: DISK STRUCTURES AND ANGULAR MOMENTUM TRANSPORT , 2011, 1110.4866.

[10]  J. Scargle.  Studies in astronomical time series analysis. II - Statistical aspects of spectral analysis of unevenly spaced data , 1982 .

[11]  L. Popović.  Super-massive binary black holes and emission lines in active galactic nuclei , 2011, 1109.0710.

[12]  D. Crenshaw,et al.  Mass Outflow from the Nucleus of the Seyfert 1 Galaxy NGC 4151 , 2006, astro-ph/0612446.

[13]  M. Gaskell,et al.  What broad emission lines tell us about how active galactic nuclei work , 2009, 0908.0386.

[14]  C. G. Mundell,et al.  The Nuclear Regions of the Seyfert Galaxy NGC 4151: Parsec-Scale H I Absorption and a Remarkable Radio Jet , 2002, astro-ph/0209540.

[15]  C. Gaskell.  Evidence for Binary Orbital Motion of a Quasar Broad-Line Region , 1996, astro-ph/9605185.

[16]  A. V. Filippenko,et al.  Evidence for a Precessing Accretion Disk in the Nucleus of NGC 1097 , 1997, astro-ph/9705176.

[17]  D. Hogg,et al.  A SYSTEMATIC SEARCH FOR MASSIVE BLACK HOLE BINARIES IN THE SLOAN DIGITAL SKY SURVEY SPECTROSCOPIC SAMPLE , 2011, 1106.1180.

[18]  L. Popović,et al.  Stratification in the broad line region of AGN: The two-component model , 2006 .

[19]  S. Ciprini,et al.  OJ 287 binary black hole system , 2011, 1112.1162.

[20]  D. Dultzin,et al.  Broad-line region physical conditions along the quasar eigenvector 1 sequence , 2010, 1007.3187.

[21]  Gas dynamics in the barred Seyfert galaxy NGC 4151 — II. High-resolution Hi study , 1998, astro-ph/9812183.

[22]  N. Lomb.  Least-squares frequency analysis of unequally spaced data , 1976 .

[23]  S. Iguchi,et al.  Orbital Motion in the Radio Galaxy 3C 66B: Evidence for a Supermassive Black Hole Binary , 2003, Science.

[24]  T. Zwitter,et al.  Eigenvector 1: An Optimal Correlation Space for Active Galactic Nuclei , 2000, The Astrophysical journal.

[25]  J. E. Pringle,et al.  Self-induced warping of accretion discs , 1996 .

[26]  M. Ulrich,et al.  Narrow and variable lines in the ultraviolet spectrum of the Seyfert galaxy NGC4151 , 1985, Nature.

[27]  J. Halpern,et al.  Structure of line-emitting accretion disks in active galactic nuclei - Arp 102B , 1989 .

[28]  M. Eracleous,et al.  Modeling of Emission Signatures of Massive Black Hole Binaries. I. Methods , 2007, 0708.0414.

[29]  M. Dopita.  Photoionising shocks in SNRs and AGN , 1995 .

[30]  J. Hutchings,et al.  Mapping the Kinematics of the Narrow-Line Region in the Seyfert Galaxy NGC 4151 , 2005, astro-ph/0505103.

[31]  M. Livio,et al.  Elliptical accretion disks in active galactic nuclei , 1995 .

[32]  J. Tao,et al.  Optical Monitoring of the Seyfert Galaxy NGC 4151 from 1997 to 2003 , 2006 .

[33]  Luis C. Ho,et al.  A Search for ``Dwarf'' Seyfert Nuclei. II. an Optical Spectral Atlas of the Nuclei of Nearby Galaxies , 1995 .

[34]  Edward J. M. Colbert,et al.  A Subparsec Radio Jet or Disk in NGC 4151 , 1998 .

[35]  S. Lubow,et al.  Mass Flow through Gaps in Circumbinary Disks , 1996 .

[36]  J. Newman,et al.  Measurement of an Active Galactic Nucleus Central Mass on Centiparsec Scales: Results of Long-Term Optical Monitoring of Arp 102B , 1997, astro-ph/9703023.

[37]  E. Pérez,et al.  An evolutionary link between Seyfert I and II galaxies , 1984 .

[38]  Massive Black Hole Binary Evolution , 2004, astro-ph/0410364.

[39]  E. Mediavilla,et al.  Contribution of a Disk Component to Single Peaked Broad Lines of Active Galactic Nuclei , 2009, 0908.2939.

[40]  C. Gammie,et al.  A gas cloud on its way towards the supermassive black hole at the Galactic Centre , 2011, Nature.

[41]  Shin Mineshige,et al.  A Supermassive Binary Black Hole with Triple Disks , 2007, 0708.2555.

[42]  M. Rees,et al.  Massive black hole binaries in active galactic nuclei , 1980, Nature.

[43]  Stanford,et al.  Rapid Formation of Supermassive Black Hole Binaries in Galaxy Mergers with Gas , 2007, Science.

[44]  T. Heckman,et al.  The Black Hole Mass of NGC 4151: Comparison of Reverberation Mapping and Stellar Dynamical Measurements , 2007, 0708.1196.

[45]  L. Popović,et al.  Long-term variability of the optical spectra of NGC 4151 - II. Evolution of the broad Hα and Hβ emission-line profiles , 2009, 0910.2980.

[46]  林 憲二,et al.  C. W. Misner, K. S. Thorne. and J. A. Wheeler : Gravitation, W. H. Freeman, San Francisco, 1973, 1279ページ, 26×21cm, $39.50. , 1975 .

[47]  D. Shoemaker,et al.  RELATIVISTIC MERGERS OF SUPERMASSIVE BLACK HOLES AND THEIR ELECTROMAGNETIC SIGNATURES , 2009, 0912.0087.

[48]  M. Milosavljevic,et al.  Formation of Galactic Nuclei , 2001, astro-ph/0103350.