MERGERS IN DOUBLE-PEAKED [O iii] ACTIVE GALACTIC NUCLEI

As a natural consequence of galaxy mergers, binary active galactic nuclei (AGNs) should be commonplace. Nevertheless, observational confirmations are rare, especially for binaries with separations less than 10 kpc. Such a system may show two sets of narrow emission lines in a single spectrum owing to the orbital motion of the binary. We have obtained high-resolution near-infrared images of 50 double-peaked [O III]λ5007 AGNs with the Keck II laser guide star adaptive optics system. The Sloan Digital Sky Survey sample is compiled from the literature and consists of 17 type-1 AGNs between 0.18 < z < 0.56 and 33 type-2 AGNs between 0.03 < z < 0.24. The new images reveal eight type-1 and eight type-2 sources that are apparently undergoing mergers. These are strong candidates of kpc-scale binary AGNs because they show multiple components separated between 0.6 and 12 kpc and often disturbed morphologies. Because most of the type-1s are at higher redshifts than the type-2s, the higher merger fraction of type-1s (47% ± 20%) compared to that of type-2s (24% ± 10%) can be attributed to the general evolution of galaxy merger fraction with redshift. Furthermore, we show that AGN mergers are outliers of the M_(BH)^-σ_∗ relation because of overestimated stellar velocity dispersions, illustrating the importance of removing mergers from the samples defining the M_(BH)^-σ_∗ relations. Finally, we find that the emission-line properties are indistinguishable for spatially resolved and unresolved sources, emphasizing that scenarios involving a single AGN can produce the same double-peaked line profiles and they account for at least 70% of the double-peaked [O III] AGNs.

[1]  S. Komossa,et al.  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 , 2009, 0908.3140.

[2]  A. Myers,et al.  SDSS J1254+0846: A BINARY QUASAR CAUGHT IN THE ACT OF MERGING , 2010, 1001.1738.

[3]  Kyle R. Stewart,et al.  MERGERS AND BULGE FORMATION IN ΛCDM: WHICH MERGERS MATTER? , 2009, 0906.5357.

[4]  Chien Y. Peng,et al.  DETAILED DECOMPOSITION OF GALAXY IMAGES. II. BEYOND AXISYMMETRIC MODELS , 2009, 0912.0731.

[5]  Integral Field Spectroscopy of the Extended Emission-Line Region of 4C 37.43* , 2006, 0705.4365.

[6]  Douglas M. Summers,et al.  The W. M. Keck Observatory Laser Guide Star Adaptive Optics System: Performance Characterization , 2006 .

[7]  L. Kewley,et al.  METALLICITY GRADIENTS AND GAS FLOWS IN GALAXY PAIRS , 2010, 1008.2204.

[8]  M. Eracleous,et al.  Double-peaked emission lines in radio-loud AGNs , 1992 .

[9]  J. Newman,et al.  INSPIRALLING SUPERMASSIVE BLACK HOLES: A NEW SIGNPOST FOR GALAXY MERGERS , 2008, 0810.3235.

[10]  L. Ho,et al.  TO APPEAR IN The Astrophysical Journal (Letters). Preprint typeset using L ATEX style emulateapj v. 26/01/00 THE MBH −σ ∗ RELATION IN LOCAL ACTIVE GALAXIES , 2005 .

[11]  C. Conselice,et al.  The DEEP2 Galaxy Redshift Survey: AEGIS Observations of a Dual AGN at z = 0.7 , 2006, astro-ph/0608380.

[12]  H. Fu,et al.  EXTENDED EMISSION-LINE REGIONS: REMNANTS OF QUASAR SUPERWINDS? , 2008, 0809.1117.

[13]  J. Newman,et al.  Rejection of the Binary Broad-Line Region Interpretation of Double-peaked Emission Lines in Three Active Galactic Nuclei , 1997, astro-ph/9706222.

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

[15]  D. Rosario,et al.  A SEARCH FOR BINARY ACTIVE GALACTIC NUCLEI: DOUBLE-PEAKED [O iii] AGNs IN THE SLOAN DIGITAL SKY SURVEY , 2009, 0908.1998.

[16]  G. Richards,et al.  A CATALOG OF QUASAR PROPERTIES FROM SLOAN DIGITAL SKY SURVEY DATA RELEASE 7 , 2011, 2209.03987.

[17]  Yue Shen,et al.  Discovery of Four kpc-Scale Binary AGNs , 2010, 1003.3467.

[18]  Maarten Schmidt,et al.  VLA observations of objects in the Palomar Bright Quasar Survey , 1989 .

[19]  L. Hernquist,et al.  Transformations of Galaxies. II. Gasdynamics in Merging Disk Galaxies: Addendum , 1996 .

[20]  Ralf Bender,et al.  THE ASTROPHYSICAL JOURNAL Preprint typeset using L ATEX style emulateapj v. 10/09/06 THE M–σ AND M–L RELATIONS IN GALACTIC BULGES, AND DETERMINATIONS OF THEIR INTRINSIC SCATTER , 2008 .

[21]  The Role of Gas in the Merging of Massive Black Holes in Galactic Nuclei. I. Black Hole Merging in a Spherical Gas Cloud , 2003, astro-ph/0310851.

[22]  R. Wainscoat,et al.  A Filter for Deep Near-Infrared Imaging , 1992 .

[23]  Yue Shen,et al.  DISCOVERY OF FOUR kpc-SCALE BINARY ACTIVE GALACTIC NUCLEI , 2010 .

[24]  Simulating the Cosmos: The Fraction of Merging Galaxies at High Redshift , 2006, astro-ph/0611187.

[25]  Yue Shen,et al.  TYPE 2 ACTIVE GALACTIC NUCLEI WITH DOUBLE-PEAKED [O iii] LINES: NARROW-LINE REGION KINEMATICS OR MERGING SUPERMASSIVE BLACK HOLE PAIRS? , 2009, 0908.2426.

[26]  S. Djorgovski,et al.  BINARY QUASARS AT HIGH REDSHIFT. I. 24 NEW QUASAR PAIRS AT z ∼ 3–4 , 2009, 0908.3907.

[27]  A. Szalay,et al.  The Sloan Digital Sky Survey Quasar Catalog. IV. Fifth Data Release , 2007, 0704.0806.

[28]  John Kormendy,et al.  Inward Bound—The Search for Supermassive Black Holes in Galactic Nuclei , 1995 .

[29]  Determining Central Black Hole Masses in Distant Active Galaxies and Quasars. II. Improved Optical and UV Scaling Relationships , 2006, astro-ph/0601303.

[30]  D. Rosario,et al.  THE JET-DRIVEN OUTFLOW IN THE RADIO GALAXY SDSS J1517+3353: IMPLICATIONS FOR DOUBLE-PEAKED NARROW-LINE ACTIVE GALACTIC NUCLEUS , 2010, 1005.0021.

[31]  B. Peterson,et al.  Optical Continuum and Emission-Line Variability of Seyfert 1 Galaxies , 1998, astro-ph/9802104.

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

[33]  J. Brinkmann,et al.  Binary Quasars in the Sloan Digital Sky Survey: Evidence for Excess Clustering on Small Scales , 2005, astro-ph/0504535.

[34]  Piero MadauEliot Quataert.  The Effect of Gravitational-Wave Recoil on the Demography of Massive Black Holes , 2004 .

[35]  R. Ellis,et al.  COSMOS: Hubble Space Telescope Observations , 2006, astro-ph/0612306.

[36]  Douglas M. Summers,et al.  The W. M. Keck Observatory Laser Guide Star Adaptive Optics System: Overview , 2006 .

[37]  T. Boroson,et al.  A candidate sub-parsec supermassive binary black hole system , 2009, Nature.

[38]  J. Mathis,et al.  The relationship between infrared, optical, and ultraviolet extinction , 1989 .

[39]  Jelle S. Kaastra,et al.  Discovery of a Binary Active Galactic Nucleus in the Ultraluminous Infrared Galaxy NGC 6240 Using Chandra , 2002 .

[40]  R. Zavala,et al.  H i OBSERVATIONS OF THE SUPERMASSIVE BINARY BLACK HOLE SYSTEM IN 0402+379 , 2009, 0902.4444.

[41]  Takamitsu Miyaji,et al.  THE BULK OF THE BLACK HOLE GROWTH SINCE z ∼ 1 OCCURS IN A SECULAR UNIVERSE: NO MAJOR MERGER–AGN CONNECTION , 2010, 1009.3265.

[42]  D. Berk,et al.  THE BLACK HOLE–BULGE RELATIONSHIP IN LUMINOUS BROAD-LINE ACTIVE GALACTIC NUCLEI AND HOST GALAXIES , 2007, 0712.1630.

[43]  R. Nichol,et al.  A search for the most massive galaxies – II. Structure, environment and formation , 2008, 0809.2602.

[44]  C. Kochanek,et al.  Why Quasar Pairs are Binary Quasars and Not Gravitational Lenses , 1997, astro-ph/9710165.

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

[46]  D. Maoz,et al.  The Relationship between Luminosity and Broad-Line Region Size in Active Galactic Nuclei , 2005, astro-ph/0504484.

[47]  Determining central black hole masses in distant active galaxies , 2002, astro-ph/0204106.

[48]  Richard L. White,et al.  The FIRST Survey: Faint Images of the Radio Sky at twenty centimeters , 1995 .

[49]  J. Bloom,et al.  THE QUASAR SDSS J1536+0441: AN UNUSUAL DOUBLE-PEAKED EMITTER , 2009, 0906.0849.

[50]  T. Treu,et al.  THE LICK AGN MONITORING PROJECT: THE MBH–σ* RELATION FOR REVERBERATION-MAPPED ACTIVE GALAXIES , 2010, 1004.0252.

[51]  Completion of a Survey and Detailed Study of Double-peaked Emission Lines in Radio-loud Active Galactic Nuclei , 2003, astro-ph/0309149.

[52]  A. Myers,et al.  Clustering Analyses of 300,000 Photometrically Classified Quasars. II. The Excess on Very Small Scales , 2006, astro-ph/0612191.

[53]  Laird M. Close,et al.  PG 1700+518 Revisited: Adaptive-Optics Imaging and a Revised Starburst Age for the Companion , 1998, astro-ph/9803333.

[54]  A massive binary black-hole system in OJ 287 and a test of general relativity , 2008, Nature.

[55]  W. Keel,et al.  The Nature of Optical Features in the Inner Region of the 3C 48 Host Galaxy , 2007, astro-ph/0701539.

[56]  A. Myers,et al.  Quasar Clustering at 25 h−1 kpc from a Complete Sample of Binaries , 2007, 0709.3474.

[57]  Close supermassive binary black holes , 2009, Nature.