RECOILING BLACK HOLES IN GALACTIC CENTERS

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RECOILING BLACK HOLES IN GALACTIC CENTERS

• Michael Boylan-Kolchin, Chung-Pei Ma, and Eliot
  Quataert (UC Berkeley)
• astro-ph/0407488

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Outline

• supermassive black hole binary formation and
  coalescence
• gravitational radiation recoil
• effects of recoil on stellar distributions
• comparison with early-type galaxies

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Supermassive Black Holes and LCDM

• hierarchical cosmology SMBHblack hole binaries
• tdf ltlt tH only for major mergers
• BH coalescence rate determined by both
  cosmological and galactic physics galaxy merger
  rate ? BH merger rate!

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Why 1 parsec should matter to a cosmologist

• if ab shrinks by a factor of 150, gravitational
  wave emission causes rapid coalescence

How? gravitational slingshot
Problem need mass of stars
but loss cone only contains enough stars to
reduce ab by a factor of 10 (i.e. M??)
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Gravitational Radiation Recoil

• Anisotropic emission of gravitational waves gives
  a kick to the newly-formed BH
• Recoil velocity depends on BH mass ratio, BH
  spins, and spin alignment
• Recoil velocity can reach 100-500 km/s (Favata et
  al. 2004)
• Many consequences - Merritt et al. Madau
  Quataert Haiman (all 2004)

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Does radiation recoil have observable effects on
elliptical galaxies?

• Plan use purely gravity N-Body experiments
  (GADGET) to study the effects of gravitational
  radiation recoil
• simulate a kicked black hole, and follow the
  evolution of the stellar density and velocity
  profiles and trajectory of the black hole

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Initial Conditions
Use the equilibrium distribution function to set
up the particles phase space coordinates
MBH0
MBHM/300
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Effects on the Stellar Density
M1010 Msun, a1 kpc vesc293 km/s2.82
vcirc tdyn26 Myr rh0.089 a89 pc
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Long-term evolution
tdyn26 Myr
vltvesc
vgtvesc
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No dynamical friction
dynamical friction
? Dynamical friction enhances core formation
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Additional Effects

• flattened density profile ? core in surface
  brightness profile
• small change of the inner velocity dispersion
• effects should be largest in galaxies with
  smallest vcirc(a)/vesc and for largest MBH/M

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Faber et al. (1997)
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So why do power-law ellipticals (without
central cores) exist?

• power-law galaxies are typically less massive
  than core ellipticals, so the effect of a kick
  should be more pronounced
• power-law galaxies seem to host central black
  holes

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Does gas play a role?

• Faber et al. (1997) gas-rich mergers could lead
  to power-law galaxies
• problem requires that starburst duration is long
  enough to counteract both binary coalescence
  effects and radiation recoil effects
• solution can gas accelerate the coalescence
  process?

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Escala et al. (2004)
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Conclusions

• supermassive BHs hierarchical cosmology
  binary black holes
• radiation recoil can lead to cores in stellar
  systems analogous to those seen in some early
  type galaxies
• gas may play an important role in enabling binary
  BHs to coalesce in turn, this may help explain
  the existence of power-law early-type galaxies
  that form hierarchically