Supermassive Black Hole Growth from Cosmological N-body Simulations

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Supermassive Black Hole Growth from Cosmological
N-body Simulations

• Miroslav Micic
• Kelly Holley-Bockelmann
• Steinn Sigurdsson
• Tom Abel

Want more info? See astro-ph/0703540
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Original goal approach SMBH merger rates from
the opposite direction of EPS

• EPS-derived BH merger rates (per year)
• 0.1 100 Haehnelt 94
• 1 - 100 Menou et al 01
• 10 Sesana et al 04
• 15 - 350 Wyithe Loeb 03
• 15 Rhook Wyithe 05

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How binary black holes meet and merge
Galaxy merger
BHs bound
O(106) pc
O(10) pc
O(10-5) pc
Dynamical friction
3-body scattering
Gravitational radiation
O(108) yr
gt O(1010) yr!
gt O(1010) yr!
in a static spherical galaxy with permanent
ejections and no resonances
not anymorethanks to excision and AMR
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10 Mpc3 from z40-0 with 2 Mpc refined
sphere Mlow 5.6 x 107 M? rlow4 kpc N2
x 106 Mhigh 8.9 x 105 M? rhigh2 kpc N5 x
106
The nuts and bolts
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Zooming into a group-sized volume of the universe
Micic, HB, and Sigurdsson
?matter 0.3 ?baryon 0.045 ?dark energy
0.7 n1 ?8 0.9 h0.7
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Strategy Pop III seeds and fast, efficient
mergers

• identify all the halos at z20, and seed those
  with M gt few 107 M? with
• 200 M? BHs
• continue seeding new halos until z12 (Pop III
  star formation squelched by UV background)
• Trace the evolution of halos and their embedded
  BHs from z 20-0.
• Assume that BHs merge once the halos merge.
• Explore three accretion schemes
• Dry mergers only
• Salpeter accretion excited by at least 41
  mergers.
• Salpeter accretion excited by M1M2 lt 101
  mergers.

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M 31
Sgr A
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High mass ratio 1000 M? mergers dominate 2ltzlt6
? ULXs?
Max black hole merger rate is 55 per year
Low mass ratio, 1000 M? BH mergers most
abundant overall
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Intermediate and Supermassive BH Growth

• BH merger rates 55 per year
• Forming a 106 M? SMBH requires major merger gas
  accretion
• To form a 107 M? SMBH must also enlist gas
  accretion during minor mergers
• Largest SMBH is in place by z 6, thereafter
  growth by mergers only (AGN era ? LISA era?)
• Lots of rogue IMBHs in a Milky Way-sized halo!

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A gravitational wave implication
Next paper Can LISA be used as a tool to
constrain BH growth mechanisms?

• new IMBH-SMBH merger source with rates gt O(10)
  per year

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and a surprise BH mass a product of environment

• a few isolated halos have extremely underweight
  bhs

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Following the leads with better dynamics
Suppression mechanisms

• gravitational wave kicks!
• proper treatment of dynamical friction

Cosmic variance -- several realizations of same
volume (105 CPU hrs)
How robust is this merger rate?
Smooth accretion tidal disruption capture and
inspiral Do those BHs in the isolated
halos stay vastly underweight? How does
this relate to downsizing?
Explore rogue black hole dynamics within Milky
Way halo Smaller volume, better resolved
simulation 1 pc resolution with on the fly BH
mergers
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Spitballing Is there a variable spread in
M-sigma?
Largest SMBHs require all accretion mechanisms
kicks inefficient (early growth)
IMBHs have many formation/growth channels kicks
efficient
Ho et al 2003