Dynamics of Galaxy Cores and Supermassive Black Holes

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Dynamics of Galaxy Cores and Supermassive Black
Holes

• David Merritt
• Santa Fe, July 2006

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Nuclear Structure
Most spheroids are well fit by Sersic profiles
at all radii
NGC 4762
Elliptical galaxy, or bulge of spiral galaxy.
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Nuclear Structure
Bright spheroids exhibit mass deficits, or cores.
NGC 4406
MV lt -21.5
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Nuclear Structure
Bright spheroids exhibit mass deficits, or
cores. The core radius is the SBH influence
radius. The core mass is the SBH mass.
NGC 4406
rcore
MV lt -21.5
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Nuclear Structure
Faint spheroids exhibit central excesses, or
nuclei.
NGC 4482
MV gt -18
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Nuclear Structure
Faint spheroids exhibit central excesses, or
nuclei. The nuclear luminosity is 10-3.5 times
the total luminosity. The nucleus is typically
unresolved.
NGC 4482
MV gt -18
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Nuclear relaxation times show a clear dependence
on spheroid luminosity. Most nuclei are
collisionless, i.e. TR gtgt 1010 yr.
16 Gyr
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Nuclear relaxation times show a clear dependence
on spheroid luminosity. ?The structure of bright
spheroids should still reflect the details of
their formation.
core
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Nuclear relaxation times show a clear dependence
on spheroid luminosity. ?The structure of faint
spheroids should correspond to collisional
states.
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Bahcall-Wolf Solution
Two-body encounters lead to a redistribution of
stars in energy space
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Bahcall-Wolf Solution
Two-body encounters lead to a redistribution of
stars in energy space
The most relevant solution is FE 0 (zero
flux), which implies, in the potential of the BH
The exact solution has FE 0 the flux is
limited by the rate at which stars diffuse into
the black hole.
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Elapsed time 1 TR
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0.2rh
Radius of cusp 0.2 rh
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The Galactic center star cluster has a density
profile that is consistent with the Bahcall-Wolf
form, though perhaps shallower.
0.2rh
Schödel et al. 2006
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In fact, loss of stars into the black hole is
dominated by changes in J, not E. Write this loss
term as FJ(E). Then
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In fact, loss of stars into the black hole is
dominated by changes in J, not E. Write this loss
term as FJ(E). Then
FJ(E) is large, in the sense that a mass MBH
should be scattered into the black hole in a time
TR.
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Stellar Disruption Rates
Wang Merritt 2004
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In fact, loss of stars into the black hole is
dominated by changes in J, not E. Write this loss
term as FJ(E). Then
and a steady state requires
i.e. the loss ?FJ dE into the black hole must be
balanced by downward diffusion in energy.
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Nuclear Expansion due to a Black Hole
M32
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Multi-Mass Evolution
Nuclear Expansion due to a Black Hole
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Massive remnants/stellar-mass BHs
Low-mass (observed) stars
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Observed stars
Particle dark matter
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core
Graham 2004
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Observed Mass Deficits
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Observed Mass Deficits
Mdef 1? MBH
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An inspiralling black hole displaces stars.
Ebisuzaki, Makino Okumura 1991
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An inspiralling black hole displaces stars.
Lagrange radii
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An inspiralling black hole displaces stars.
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140
Separations
astro-ph/0603439
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astro-ph/0603439
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astro-ph/0603439
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i. e. Mdef 0.5(m1m2)
astro-ph/0603439
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But, mass deficits are cumulativeMdef
0.5NmergeMBH,
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110
astro-ph/0603439
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But, mass deficits are cumulativeMdef
0.5NmergeMBH, i.e. observed mass deficits are
consistent with bright E-galaxies having
experienced 2-3 dry mergers since black hole
formation.
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110
astro-ph/0603439
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The observed (projected) separation of 7 pc is
the expected stalling radius for a 109 Msun
black hole.
Rodriguez et al. 2006
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Core formation by binary SBHs removes the need
for two families of elliptical
galaxies (Kormendy 1985).
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Core formation by binary SBHs removes the need
for two families of elliptical
galaxies (Kormendy 1985).
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Bright galaxies once had higher central
densities/surface brightnesses. (Jerjen
Binggeli 1997, Graham Guzman 2003)
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In a collisional nucleus like that of the Milky
Way, a density cusp can regenerate after being
destroyed by a binary black hole.
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Orbit families in triaxial potentials.
Poon 2002
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Binary evolution in spherical galaxy.
Binary evolution in triaxial galaxy.
Berczik et al. 2006
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Berczik et al. 2006
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Triple (Multiple) Black Holes
Harfst Bischof 2006
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