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 NGC 6240 z = 0.02!x = 0.7 kpc Komossa et al. 2003 AGN AGN Mrk 463 z = 0.05!x = 4 kpc Bianchi et al. 2008 0402+379 z = 0.06!x = 7 pc Rodriguez et al. 2006
A Large Observational Sample of Dual AGN Would Measure: What is the galaxy merger rate? How much do supermassive black holes grow in mass through gas accretion during galaxy mergers? NASA What is the supermassive black hole merger rate? ACS/NASA
A Large Observational Sample of Dual AGN Would Measure: 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? Gültekin et al. 2009
A Large Observational Sample of Dual AGN Would Measure: What is the galaxy merger rate? Gravitational waves produced by supermassive black hole binaries How much do supermassive black holes grow in mass through gas accretion during galaxy mergers? should be detected by pulsar timing arrays C. Henze/NASA What is the supermassive black hole merger rate? NRAO
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 340 double-peaked AGN in SDSS H" [O III] Wang et al. 2009 Liu et al. 2010 Smith et al. 2010
But, Double Peaks Can Also Be Produced by AGN Outflows Mrk 78 at z=0.04 (Fischer et al. 2011) [O III] #4959 [O III] #5007
But, Double Peaks Can Also Be Produced by AGN Outflows Mrk 78 at z=0.04 (Fischer et al. 2011) [O III] λ5007
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: [O III] in dual AGN: [O III] λ5007 Fischer et al. 2011 Comerford et al. 2011a
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 10 PA=170.5 ] x 2 ] x 1 PA=80.5!v ] separation x 1 at position angle θ 1 separation x 2 at position angle θ 2 full separation on the sky Δx position angle on the sky θ sky x 1 cos (" sky #" 2 ) = x 2 cos (" sky #" 1 ) "x = x 1 /cos(# sky $# 1 )
The Double Peaks Are Produced by Kpc-scale Dual AGN or Outflows 0.2 kpc < Δx < 5.5 kpc Median Δx = 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 <100 pc, small-scale AGN outflows" # kpc-scale dual AGN or kpc-scale AGN outflows Comerford et al. 2011b! AGN pairs or AGN outflows on scales ~10 kpc"
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): [O III] λ5007 Fischer et al. 2011 Rosario et al. 2010
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 15 kpc Dual AGN expected to be aligned with host galaxy major axis (seen in simulations of dual AGN) 15 kpc In contrast, AGN outflows have a range of orientations within host galaxy Blecha et al. 2012
The Most Promising Candidates for Dual AGN Good Candidates The 14 objects with Δθ 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 Comerford et al. 2011b (McGurk et al. 2011; Fu et al. 2011) McGurk et al. 2011 Fu et al. 2011 Chandra observations upcoming!
X-ray 3. For Definitive Proof of Dual AGN, Need X-ray or Radio Detections Upcoming Chandra observations for 13 dual AGN candidates X-ray Radio Radio Komossa et al. 2003 Rodriguez et al. 2006 Jansky VLA proposals submitted for 20 dual AGN candidates Hubble Space Telescope z=1.2 HST Upcoming HST observations for 10 of the Chandra targets; will reveal double stellar nuclei, tidal features, stellar populations Barrows et al. 2012
Proof of Concept: X-ray Confirmation of Dual AGN SDSS J171544+600835 z=0.16 Δv=350 km/s, Δx=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 Chandra/ACIS Comerford et al. 2011a
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 doublepeaked 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