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  • Dual Supermassive Black Holes as Tracers of Galaxy Mergers

    Julie Comerford

    NSF Astronomy and Astrophysics Postdoctoral Fellow University of Texas at Austin

    Collaborators: Michael Cooper, Marc Davis, Mike Eracleous, Karl Gebhardt, Brian Gerke, Jenny Greene, Roger Griffith, Fiona Harrison, Greg Madejski, Kristin Madsen, Claire Max, Rosalie McGurk, Jeff Newman, Dave Pooley,

    Dan Stern, Ben Weiner, Joan Wrobel

  • Dual Supermassive Black Holes Are the Smallest Separation Black Hole Pairs that

    Can Be Confirmed (Currently)

    Binary Quasars

    Dual SMBHs or Dual AGN Binary SMBHs

  • There Should Be Many Dual AGN at Kpc-scale Separations

    Can identify dual supermassive black holes observationally if they power dual AGN

    Simulations of galaxy mergers show there should be lots of dual AGN visible at < 10 kpc separations

    Van Wassenhove et al. 2011

  • We Expect Dual AGN in Merger-remnant Galaxies, Yet

    Very Few Have Been Found

    AGN AGN

    Mrk 463 z = 0.05 !x = 4 kpc Bianchi et al. 2008

    NGC 6240 z = 0.02 !x = 0.7 kpc Komossa et al. 2003

    0402+379 z = 0.06 !x = 7 pc Rodriguez et al. 2006

  • A Large Observational Sample of Dual AGN Would Measure:

    NASA

    ACS/NASA

    What is the galaxy merger rate?

    How much do supermassive black holes grow in mass through gas accretion during galaxy mergers?

    What is the supermassive black hole merger rate?

  • A Large Observational Sample of Dual AGN Would Measure:

    Gltekin et al. 2009

    What is the galaxy merger rate?

    How much do supermassive black holes grow in mass through gas accretion during galaxy mergers?

    What is the supermassive black hole merger rate?

  • A Large Observational Sample of Dual AGN Would Measure:

    C. H

    en

    ze/N

    ASA

    What is the galaxy merger rate?

    How much do supermassive black holes grow in mass through gas accretion during galaxy mergers?

    What is the supermassive black hole merger rate?

    Gravitational waves produced by supermassive black hole binaries

    should be detected by pulsar timing arrays

    NR

    AO

  • Goal: Build a Large Catalog of Dual AGN to Use as Tracers of Galaxy Mergers, Black

    Hole Growth, and Black Hole Mergers

    Need systematic approach to advance from individual systems to assembling a large catalog of dual AGN

    Begin by selecting candidate dual AGN in large spectroscopic surveys or imaging surveys of galaxies

  • Three Steps to Finding Dual AGN in Spectroscopic Surveys

  • 1. Select Dual AGN Candidates as Galaxies with Double-peaked

    AGN Emission Lines

    [O III] H"

    Smith et al. 2010 Liu et al. 2010 Wang et al. 2009

    340 double-peaked AGN in SDSS

  • But, Double Peaks Can Also Be Produced by AGN Outflows

    Mrk 78 at z=0.04 (Fischer et al. 2011)

    [O III] #5007 [O III] #4959

  • Mrk 78 at z=0.04 (Fischer et al. 2011)

    But, Double Peaks Can Also Be Produced by AGN Outflows

    [O III] 5007

  • Determining the Nature of Double-Peaked AGN Emission Lines

    2. Obtain follow-up longslit spectroscopy to determine the spatial extent of the AGN emission and help determine the source of the emission

    [O III] in AGN outflow:

    Fischer et al. 2011

    [O III] in dual AGN:

    Comerford et al. 2011a

    [O III] 5007

  • Use Longslit Spectroscopy to Identify the Most Promising Dual AGN Candidates

    Obtained Lick, Palomar, and MMT longslit spectroscopy for 81 of the 340 SDSS double-peaked AGN (0.03 < z < 0.69)

    10

  • Measure Physical Separation and Orientation of the Two Emission

    Components on the Sky

    x2

    x1 ]

    ]

    separation x1 at position angle 1 separation x2 at position angle 2

    full separation on the sky x position angle on the sky sky

    !

    x1 cos " sky #"2( ) = x2 cos " sky #"1( )

    !

    "x = x1 /cos # sky $#1( )

    ]!v

    10 PA=170.5

    PA=80.5

  • The Double Peaks Are Produced by Kpc-scale Dual AGN or Outflows

    Comerford et al. 2011b

    0.2 kpc < x < 5.5 kpc Median x = 1.1 kpc This means that the mechanism(s) producing double-peaked AGN are neither very small-scale nor very large-scale effects

    ! Rotation of gas in disks

  • Spatial Extent of AGN Emission 58% exhibit spatially-compact emission components

    42% exhibit spatially-extended emission components

  • Spatially-extended AGN Emission Reminiscent of AGN Outflows

    AGN outflow in Mrk 78 (z=0.04):

    AGN outflow in SDSS J1517+3353 (z=0.14):

    Fischer et al. 2011 Rosario et al. 2010

    [O III] 5007

  • Use Orientation of Double AGN Emission Components within Host Galaxy to

    Identify Promising Dual AGN Candidates

    "sky

    !"

  • Use Orientation of Double AGN Emission Components within Host Galaxy to

    Identify Promising Dual AGN Candidates

    Dual AGN expected to be aligned with host galaxy major axis (seen in simulations of dual AGN)

    In contrast, AGN outflows have a range of orientations within host galaxy

    Blecha et al. 2012

    15 kpc

    15 kpc

  • The Most Promising Candidates for Dual AGN

    Good Candidates The 14 objects with consistent with zero, since we expect dual AGN in the plane of the host galaxy

    Best Candidates The 3 objects with double AGN emission components with the same spatial separation and orientation on the sky as the double stellar nuclei seen in adaptive optics image (McGurk et al. 2011; Fu et al. 2011)

    McGurk et al. 2011

    Comerford et al. 2011b

    Chandra observations upcoming!

    Fu et al. 2011

  • 3. For Definitive Proof of Dual AGN, Need X-ray or Radio Detections

    X-ray

    Upcoming Chandra observations for 13 dual AGN candidates

    Radio

    Jansky VLA proposals submitted for 20 dual AGN candidates

    Hubble Space Telescope

    Upcoming HST observations for 10 of the Chandra targets; will reveal double stellar nuclei, tidal features, stellar populations

    Komossa et al. 2003

    HST

    X-ray

    Rodriguez et al. 2006

    Radio

    Barrows et al. 2012

    z=1.2

  • Proof of Concept: X-ray Confirmation of Dual AGN

    SDSS J171544+600835 z=0.16 v=350 km/s, x=1.9 kpc (0.68), PA=147 E of N

    Double emission components in longslit observations coincide with double X-ray sources in Chandra observations

    Comerford et al. 2011a

    Chandra/ACIS

  • Progress towards Building a Large Catalog of Dual Supermassive Black Holes

    2008: 3 known dual supermassive black holes, discovered serendipitously Systematic search begins

    2012: 40 known dual supermassive black holes, most discovered through systematic searches Observers: Comerford et al. 2009ab, 2011ab; Wang et al. 2009; Smith et al. 2010; Liu et al. 2010ab; Shen et al. 2011; McGurk et al. 2011; Fu et al. 2011ab; Fu et al. 2012; Rosario et al. 2011; Tingay & Wayth 2011;

    Fabbiano et al. 2011; Barrows et al. 2012; Koss et al. 2011, 2012 Theory and simulations: Shen & Loeb 2010; Yu et al. 2011; Van Wassenhove et al. 2011; Blecha et al. 2012

    2013 - 2014: >100 known dual supermassive black holes, given the dozens of strong candidates in the queue for confirmation

  • A Systematic Search for Dual AGN 1. Identify dual AGN candidates as double-peaked AGN in spectroscopic surveys (e.g., SDSS, DEEP2)

    2. Obtain follow-up observations (e.g., longslit spectroscopy, imaging) to identify most promising dual AGN candidates

    3. Obtain follow-up X-ray/radio observations to confirm or refute dual AGN nature (13 candidates approved for Chandra, 10 candidates approved for HST, 20 candidates submitted to Jansky VLA)

    Use large catalog of dual AGN to probe galaxy merger rate, supermassive black hole growth, and supermassive black hole merger rate

    Result from DEEP2 dual SMBHs: ~3 mergers/Gyr for red galaxies at 0.3 < z < 0.8 (Comerford et al. 2009a)

    SDSS DEEP2

    HST

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