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Gas Driven Supermassive Black Hole Binaries: periodic quasar variability and the gravitational wave background. Bence Kocsis (CFA). Einstein Symposium, 10/26/2009. Galaxies merge ignite quasars black holes merge AGN variability surveys and Pulsar Timing Arrays detects them. - PowerPoint PPT Presentation
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Gas Driven Supermassive Black Hole Binaries: periodic quasar variability and thegravitational wave backgroundBence Kocsis (CFA)Einstein Symposium, 10/26/2009
Galaxies merge ignite quasars black holes merge AGN variability surveys and Pulsar Timing Arrays detects them
Evolution of binariesCollisionless damping (~kpc; dynamical friction, Landau damping)3-body encounters with stars (~ 1 pc)Gas driven migration (~0.1 pc, Type II migration)Gravitational waves (~0.01 pc)Note: sub-parsec SMBH binaries ~ weeks months orbital periods~ 103 104 km/s velocity
Evolution of binariesCollisionless damping (~kpc; dynamical friction, Landau damping)3-body encounters with stars (~ 1 pc)Gas driven migration (~0.1 pc, Type II migration)Gravitational waves (~0.01 pc)Note: sub-parsec SMBH binaries ~ weeks months orbital periods~ 103 104 km/s velocityNumber of binaries reduced at corresponding separation due to gas!
Within the last pcThin gaseous diskDisk aligns with binary plane (Bardeen & Peterson 1975, Ivanov et al. 1999)Binary evacuates cavity (Artymowicz & Lubov 1994)Viscous decay (Type II migration)Secondary dominatedDisk dominatedGravitational Wave driven evolutionCuadra et al. 2009; see also Ivanov et al. 1999; Armitage & Natarayan 2002, 2005; MacFadyen & Milosavljevic 2008;
Within the last pcThin gaseous diskDisk aligns with binary plane (Bardeen & Peterson 1975, Ivanov et al. 1999)Binary evacuates cavity (Artymowicz & Lubov 1994)Viscous decay (Type II migration)Secondary dominatedDisk dominatedGravitational Wave driven evolutionCuadra et al. 2009; see also Ivanov et al. 1999; Armitage & Natarayan 2002, 2005; MacFadyen & Milosavljevic 2008;Accretion Rate
Within the last pcThin gaseous diskDisk aligns with binary plane (Bardeen & Peterson 1975, Ivanov et al. 1999)Binary evacuates cavity (Artymowicz & Lubov 1994)Viscous decay (Type II migration)Secondary dominatedDisk dominatedGravitational Wave driven evolutionHaiman, Kocsis, Menou, 2009, ApJ, 700, 1952Residence Time
Within the last pcThin gaseous diskDisk aligns with binary plane (Bardeen & Peterson 1975, Ivanov et al. 1999)Binary evacuates cavity (Artymowicz & Lubov 1994)Viscous decay (Type II migration)Secondary dominatedDisk dominatedGravitational Wave driven evolutionHaiman, Kocsis, Menou, 2009, ApJ, 700, 1952Residence Time
Detecting Decaying binariesOptimistic Assumptions:binary is producing bright emission (~30% Ledd)non-negligible fraction (~10%) of this emission is variableclearly identifiable period tvar~ torbitin-spiraling binary = periodically variable quasarIdentifying such binaries statistically?fraction of quasars with period tvar = (1+z) torbfvar = tres / tQ
Requirements for an (optical) surveyfor finding periodic variable sourcesRequire: 100 sources @ tvar 1 yr 5 sources @ tvar 20 wk
Assume: fEdd= 0.3 fvar = 0.1 tQ = 107 yr Hopkins et al. QSOLF @ z=2Conclude: wide survey best to probe GW-decay disk physics at i~26.5Haiman, Kocsis, Menou, 2009, ApJ, 700, 1952
Pulsar Timing Arrays
PPTA (Parkes pulsar timing array) LEAP (large European array for pulsars) NanoGrav (north American nHz observatory for gravitational waves)
GW background for PTAsCharacteristic gravitational wave (GW) signal
Merger history Millennium Run (Springel et al. 2005; Sesana et al. 2009)
Residence time at sub-pc scales From our previous plot
Millennium Run
Gravitational Waves for PTAsGas OFFGas ONContribution of individual sourcesUnresolved backgroundTotal signalSpectrum averaged over 1000 Monte Carlo realizationsKocsis & Sesana (2009)
SummarySMBH binaries, gas/GW driven dynamics
AGN surveysLook for week-month year periodic variabilityLook for spectral features ~ several x 1,000 km/s
Pulsar Timing ArraysGas suppresses the stochastic background Individually resolvable sources remain
Higher signal variance: impossible to characterize the slope of the background a prioriStatistics of resolvable sources basically unaffected
GW background for PTAsCharacteristic gravitational wave (GW) signalThis depends onMerger history Millennium Run (Springel et al. 2005; Sesana et al. 2009)Residence time at subparsec scales From our previous plotMillennium Run
Millennium simulation (Springel et al. 2005)N-body numerical simulation of halo hierarchySemi-analytical models for galaxy formation and evolutionWe extract catalogs of merging galaxies and populate them with sensible MBH prescriptionsSMBH Merger history
Cartoon Model of Binary + Gas evolutionGas cools and settles into a thin circumbinary diskDisk aligned with binary orbital plane (Bardeen & Peterson 1975, Ivanov et al. 1999)Torques from binary evacuate central cavity r ~ 2a(Artymowicz & Lubov 1994)Orbit decays due to torques and viscosity, gas followsAnalogous to Type II planetary migrationWhen local disk mass < binary mass migration slows downtGW becomes shorter than tvis when r ~ 100 RS
Punctured disk