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Equal- and unequal-mass mergers of disk and elliptical galaxies with black holes

Equal- and unequal-mass mergers of disk and elliptical galaxies with black holes. Peter Johansson University Observatory Munich. 8 th Sino-German workshop on galaxy formation and cosmology Kunming, February 26 th , 2009. Johansson, Naab , Burkert , 2009, ApJ , 690, 802.

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Equal- and unequal-mass mergers of disk and elliptical galaxies with black holes

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  1. Equal- and unequal-mass mergers of disk and elliptical galaxies with black holes Peter Johansson University Observatory Munich 8th Sino-German workshop on galaxy formation and cosmology Kunming, February 26th, 2009 Johansson, Naab, Burkert, 2009, ApJ, 690, 802

  2. The role of AGN feedback • 1) Observed relic supermassive black holes - quasars. • 2) Observed ULIRGs, merging galaxies with intense starburst and/or AGN activity. • 3) The observed MBH-σ & MBH-MBULGE relations. The coeval growth of black holes and galaxy bulges. • Simplified feedback energetics: SN/AGN- energy coupling/location: • Supernova II feedback • AGN feedback

  3. BH feedback model: Accretion • The Schwarzschild radius of a SMBH with M~107 Msunis RS~10-6 pc. Numerical Galaxy simulations at best resolve details down ~10 pc -> effective subresolution model. • Use the Tree-SPH GADGET-2 code (Springel et al. 2005) with cooling+SF+SNfeedback+BH feedback based on aBondi-Hoyle accretion model(Bondi 1952): α~100

  4. BH feedback model: Energetics • The radiative efficiency εr~0.1 (Sunyaev&Shakura 1973) and the thermal coupling εf~0.05 resulting in a total BH feedback energy efficiency of = 0.5%. • The SPH kernel is used to calculate the average gas density, temperature as well as the gas bulk velocity relative to the BH. • The BH mass grows stochastically by absorption of gas particles, include also smooth internal black hole mass, which is used to determine the accretion rate. • BHs will merge instantly if they come within a smoothing length and if their relative velocity is smaller than the local soundspeed. • Thermal FB energy distributed weighted within the SPH kernel.

  5. Model setup and BHs in isolated galaxies Isolated galaxies • Using the Springel (2000) method based on Hernquist (1993) we setup disk galaxies with Hernquist DM profiles+bulges& exponential discs with fgas=20%, 40%, 80%. • The BH is initially at rest in the centre of each model galaxy with a seed mass of 105 Msun. • We simulate a sample of isolated galaxies, 1:1 and 3:1 mergers, dry E-E and mixed E-Sp mergers.

  6. Numerical techniques ensuring BH merging 3:1 merger. Tests of BH merging prescription • The momentum is conserved in BH mergers. • For unequal-mass mergers ‘repositio-ning’ of the BHs at the position of the minimum of the potential. • The standard pre-scription is adequate for equal-mass mergers.

  7. 3:1 merger movie Total SFR Total MBH X-Y projection: Gas + BHs

  8. Varying the initial gas fraction and orbit 3:1 mergers • Variations in the initial gas mass fraction produce large differences in the final BH mass, 20%, 40%, 80%. • Variations in orbital geometry for a fixed initial gas mass fraction produce small differences in the final BH mass, shades of blue.

  9. BH accretion as a function of merger mass ratio • Systematic variations as a function of merger mass ratio.

  10. MBH-σ & MBH-M*relations for 3:1 and 1:1 mergers MBH-σ MBH-M* Lines: Observed relations - Tremaine et al. (2002) and Häring&Rix (2004).

  11. SFR&BH accretion for mixed and dry mergers Dry mergers (E-E) : fBH,ins~1-10% Mixed mergers (E-Sp): fBH,ins~20-30%

  12. MBH-σ & MBH-M*relations for mixed mergers MBH-σ MBH-M*

  13. MBH-σ & MBH-M*relations for dry mergers MBH-σ MBH-M*

  14. BHFP for disk and elliptical mergers 1:1 & 3:1 disk-disk mergers (Sp-Sp) Mixed&dry mergers (E-Sp&E-E) • Black hole fundamental plane (BHFP, Hopkins et al. 2007) MBH~s3.0±0.3R0.43±0.19or MBH~M*0.54±0.54s2.2±0.5. • Statistically equivalent formulation MBH-Ebind, Ebind~M*s2. • Lines: Observed relation from Hopkins et al. 2007: • log(MBH/Msun)=8.23±0.06+(0.71±0.06)log(M*σ2/ M0σ02)

  15. Conclusions/Summary • The simple BH accretion/feedback model works remarkably well in reproducing the observed MBH-σ,MBH-MBULGE & MBH-Ebindrelation for equal, unequal, E-E dry and mixed mergers. • The relation is the result of large-scale gas flows to the center of the galaxy and the self-regulation of MBH due to feedback energy. • Star formation is efficiently terminated in low merger ratio Sp-Sp mergers (≤3:1) and in mixed and dry mergers. • The global properties of the galaxy are insensitive to the details of the BH feedback model, but what about the detailed properties? Surface density profiles, kinematics, orbits... • Potential model improvements: Include spin of the BH, more physical accretion model, quasar mode vs. radio mode, jets....

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