Dual and Binary MBHs and AGN: Connecting Dynamics and Accretion

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1 Dual and Binary MBHs and AGN: Connecting Dynamics and Accretion Sandor Van Wassenhove Marta Volonteri Lucio Mayer Jillian Bellovary Massimo Dotti Simone Callegari

2 BH-Galaxy Coevolution Black holes found in the centers of most nearby galaxies Scaling relations point toward coevolution of galaxy and BH BHs should naturally grow along with galaxies through accretion and mergers and influence the galaxy through feedback Gultekin et al. 2009

3 How do BHs grow? BH-BH Mergers Accretion Observables? Gravitational Waves AGN/Quasars

4 Motivating Questions How do scaling relations evolve during a merger? When and where do BHs grow most efficiently? Do BHs merge as efficiently as their host galaxies? How can we link observations of BH activity (dual/binary) AGN and gravitational waves - to the properties of the hosts?

5 Simulation Setup Merging isolated galaxies containing BHs using N-body SPH code Gasoline Focusing on typical mergers for ΛCDM cosmology high redshift (z=3), unequal mass mergers (1:2, 1:4, 1:10) Considering gas poor (elliptical) and gas-rich (spiral) primary galaxies Coplanar and inclined (45 degrees) orbits Study which mergers lead to efficient accretion, dual AGN, and successful pairing leading to the binary phase

6 Galaxy Merger: Early Stages Both galaxies and BHs grow quiescently 1:2 Spiral-Spiral Merger AGN luminosities remain low, generally <10 43 erg/s AGN activity is not triggered by galaxy dynamics, any dual activity is random Van Wassenhove et al. 2012

7 Galaxy Merger: Late Stages Tidal forces trigger strong gas inflows in both galaxies 1:2 Spiral-Spiral Merger Star formation rates and AGN activity peak together following pericenter passages BHs reach erg/s and have better correlated accretion, producing dual AGN activity End simulation when BH separation reaches our resolution limit (~10 pc) Van Wassenhove et al. 2012

8 1:2 Coplanar Spiral-Spiral

9 Scarcity of Dual AGN If all galaxies host BHs and galaxy mergers trigger accretion, duals should be common. Optical surveys: Search for galaxy spectra with pairs of AGN emission lines Dual AGN fraction generally at most a few % EGSD2 J EGSD2 J Comerford et al Hard X-ray surveys: Search for AGN in companion galaxies of ultra-hard X-ray AGN Higher dual fraction than optical surveys Dual fraction increases for galaxies with small separations Koss et al. 2012

10 Observability Threshold Low threshold: active most of the simulation; lots of dual AGN High threshold: probes times when AGN accretion is triggered by merger dynamics

11 Observability Threshold Strongest activity is at small separations and velocity offsets Much of the dual activity is difficult to detect

12 Timescales 1:2 Coplanar Spiral-Spiral Threshold BH 1 BH 2 Both AGN - Dual erg/s erg/s erg/s 1047 Myr 286 Myr 36 Myr 876 Myr 207 Myr 35 Myr 703 Myr 69 Myr 12 Myr A realistic threshold cuts out most of the dual emission

13 Timescales 1:2 Coplanar Spiral-Spiral Threshold BH 1 BH 2 Both AGN - Dual erg/s erg/s erg/s 1047 Myr 286 Myr 36 Myr 876 Myr 207 Myr 35 Myr 703 Myr 69 Myr 12 Myr A realistic threshold cuts out most of the dual emission Dual Timescale Dual Fraction No cutoff d > 1 kpc d > 10 kpc v > 150 km/s 12 Myr 10 Myr 0.06 Myr 3 Myr 19.2% 16.5% 0.1% 4.8% Observational limitations reduce dual emission further to a few %, in rough agreement with optical survey results

14 Dual AGN Summary Caveats No obscuration No NLR modeling (see Laura Blecha s talk) Unresolved variability in AGN Dual AGN activity peaks at small separations stronger accretion and better correlation between BHs Constraints (luminosity, separation, velocity offset) can reduce dual fraction to be consistent with observations Koss et al. 2012

15 BH Pairing Important step on the way to BH binary and coalescence Gravitational waves from BH coalescence can be a new probe of structure formation if we understand how BH mergers are linked to galaxy properties Mass, spin, and orbits of BHs affect gravitational wave signal and are in turn determined during the galaxy merger NASA

16 The Key to Successful Pairing Unequal Mass Mergers Form a dense stellar cusp that will resist stripping and deliver the SMBH to the center of the merger remnant Callegari et al A gas rich secondary galaxy is important!

17 Inclined Coplanar Insufficient Star Formation Inclined 1:4 merger: Less central SF in the secondary leads to disruption at ~kpc separations rather than efficient pairing Weaker gas inflows and early disruption lead to significantly less dual AGN activity than in the coplanar merger

18 Pairing Results Spiral-spiral simulations end with BHs at separations of tens of parsecs in a gas rich environment binary will form soon More concentrated elliptical disrupts secondary at hundreds of parsecs binary formation delayed 1:10 Mergers Inclined mergers lead to less efficient pairing Time (Gyr) Callegari et al. 2011

19 1:2 Nucleus Disruption Strong central SF in both galaxies triggered after pericenter passages Primary Secondary SFR and mass enclosed in central 100 pc near each BH Both galaxies build up a similar amount of mass on small scales, but companion has slightly more At the fourth pericenter passage, the primary nucleus is disrupted and the primary SMBH is left orbiting around the secondary nucleus and BH

20 1:4 Nucleus Disruption Weaker SFR in primary, less perturbed by smaller companion Primary Secondary Stronger central SF in the companion almost all of the global SF occurs there Companion builds up dense cusp whereas primary does not SFR and mass enclosed in central 100 pc near each BH Primary nucleus again disrupted, but more easily than in the 1:2 merger

21 1:4 1 kpc

22 Conditions for a Nuclear Coup We certainly don t expect a dwarf galaxy to disrupt the center of the Milky Way Solution? Strip the gas away before it forms stars Inclined mergers have weaker tidal torques and slower orbital evolution Smaller companions experience stronger stripping Not enough gas available to form the necessary cusp Much smaller companion will have a low central mass and little gas Lower gas fractions less common in the local universe? What do we see in 1:10 (minor) mergers?

23 Stripping 1:10 Results Callegari et al. 2009, Callegari et al Gas completely stripped from the secondary galaxy at the 3 rd pericenter passage Lack of gas shuts down star formation and prevents dual AGN activity Inclined Inclined Low f gas Small R p Not enough central star formation for a nuclear coup Inclined or gas poor mergers produce less efficient pairing and less growth in the BH mass ratio

24 Summary Star formation and BH activity peak late in galaxy mergers much of the dual AGN activity occurs at small separations and velocity offsets, making it difficult to detect Central star formation is key to efficient pairing in unequal mass mergers In some situations, the secondary nucleus may disrupt the primary, resulting in a nuclear coup ongoing work Large scale pairing phase sets BH positions and masses as they move into the binary phase important to keep this in mind when studying binary evolution and coalescence