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Gravitational radiation from Massive Black Hole Binaries

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Galaxy mergers & MBH assembly. Black Hole Demographics ... Quickly driven to center of daughter galaxy by Dynamical Friction, followed by... – PowerPoint PPT presentation

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Title: Gravitational radiation from Massive Black Hole Binaries


1
Gravitational radiation from Massive Black Hole
Binaries
  • Andrew Jaffe
  • PTA Focus group PSU/CGWP
  • 22 July 2005
  • D. Backer, D. Dawe, A. Lommen

2
Gravitational Radiationfrom MBH Binaries
  • Ingredients
  • Galaxy mergers MBH assembly
  • Black Hole Demographics
  • Galactic dynamics the Final Parsec Problem
  • GW waveforms
  • ? Stochastic Background of MBH Binary GWs

3
Model Universe of MBH Binaries
D. Backer
4
GWs from MBH Mergers
  • Massive Black Holes in nearby galaxies...
  • MBH demographics from kinematics
  • ... and high z (AGN)
  • Modern galaxies are the result of mergers
  • Ellipticals from major mergers
  • ? MBH binaries ubiquitous
  • Quickly driven to center of daughter galaxy by
    Dynamical Friction, followed by...
  • ...Gravitational-Radiation-driven coalescence
  • IF they get close enough...

5
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6
Binary MBH GW Spectrum
  • Merger rate Mass function GWs
  • N(z, f, M1, M2) df ? ?f1f2 R(z)CO, z M-5/3 f
    -8/3df/fhc2(f) f ??dz dM1 dM2 h2(z,M) N(z,
    f, M1, M2) ?(M /108M?)5/3? (f/yr-1)-4/3
    Ih(see also Phinney 2002)nb. integral
    separates f(M) f -8/3 I(z)

Stochastic (mean-square)
M(M1M2)3/5/(M1M2)1/5
7
Gravitational Radiationfrom MBH Binaries
  • GWs from Kepler motion weak-field GR
  • P1 yr for 109 M? at 0.01 pc
  • hc(f) µ (M f )2/3 r-1 ( redshift to
    z0)
  • h10-15 for 109 M? at 1 Gpc for f1/yr
  • long lifetime at Pmonths-year
  • Pulsar Timing (Kaspi et al 1994 Rajagopal
    Romani 1995 Thorsett Dewey 1997)

8
GWs from MBH Binaries
  • Orbits circularized quickly (dynamics and/or GW)
  • hrms(f )µ (M f )2/3 r-1 M5/3chirp
  • (stochastic sum over population)
  • Cosmology, mass, frequency dependence

9
Binary formation and DynamicsApproaching the
problem
  • Pioneers
  • Begelman Blandford Rees
  • Haehnelt Kauffmann
  • Rajagopal Romani
  • Analytic (e.g., Backer J)
  • Explicit calculations of MBH binary/galaxy
    dynamics (Dawe J)
  • Semi-analytic (Extended Press-Schechter
    formalism)
  • Menou et al (0101196)
  • Wyithe Loeb (0211556)
  • Enoki et al (0404389)
  • From Halos - Galaxies (baryons)
  • Sesana et al (0401543, 0409255)
  • Some explicit MBH binary/galaxy dynamics

10
MBH CoalescenceGalaxy merger rate
  • Binary MBH formation driven by Galaxy mergers
  • Poorly-measured even at moderate z

Enoki et al 2005
11
MBH Growth
  • Coalescence dominates dM/dt for z
  • From Halos to MBHs
  • Gas physics
  • Heating, cooling, star formation
  • Accretion

Enoki et al 2005
12
Massive Black Hole Demographics
  • Roughly, M? 0.003 Msph
  • M? 108M?(s/200km/s)4.72
  • Implies accretion-dominated growth? (Silk
    Rees)
  • How to maintain in the presence of mergers?
  • (Magorrian et al, Gebhardt et al, Ferrarese
    Merritt, Tremaine et al)
  • Traces merger history and/or potential depth?
  • High z?
  • AGN activity (McClure Dunlop)

13
MBH Mass function
  • MBH Demographics roughly constant over large z
    range
  • Conversion of AGN to normal galaxies

Ferrarese 2002
14
MBH Binary dynamics
  • Dynamical friction (c.) drags black holes to
    center
  • tDF Myr (M?/108 M?)-1,Binary hardens
  • loss cone is depleted, GW timescale still H0-1
  • Need to get to a0.02 pc, P30 yr
  • Stellar Dynamics difficult (Yu 2001
    Milosavljevic Merritt 2002 ...)
  • Gas dynamics? (Gould Rix 2000 Armitage
    Natarajan 2002)
  • Wandering? 3-body interactions?
  • GW energy loss until final inspiral (1 day)
  • Successful inspiral or many MBH binaries?
  • too close to observe?
  • Absence of evidence or evidence of absence?
  • Need evidence of post-merger binary activity
    (e.g., Merritt Ekers 2002 X sources
    dual-nucleus Chandra source ...)

15
Life cycle of a MBH Binary
16
Dynamics and the low-f cutoff
  • Losing energy to stars/gas/galaxy prior to GW
    regime

Sesana et al 2004
17
The final parsec problem
  • Binary hung up before GW regime energy-loss
    timescale Hubble time H-1
  • (nb also need to take delay into account when not

Sesana et al 2004
Delayed
instantaneous
18
Timescales and the final pc problem
  • Need careful accounting of MBH Binary dynamics
  • (and galaxy merger/coalescence delay)

19
Contributions to the GW spectrum
Enoki et al 2005
20
Coalescence and the high-f cutoff
  • Quasi-Newtonian until Innermost Stable Circular
    Orbit.
  • Enoki et al high-f cutoff bend at 10-6 Hz
  • Feeds into LISA rate

Sesana et al 2004
Enoki et al 2005
21
Stochastic GW Background
22
Gravitational Waves from LISA
  • See some fraction of total event rate (only
    sensitive to events in-band M 105 M? /(1z)
  • nb. lighter MBHs inevitably more common at higher
    z
  • Individual events, not stochastic background
  • Hughes 2001 for parameter extraction

23
MBH Binaries at z1LISA Signal
24
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25
Future Work
  • Full calculation/measurement of Galaxy (MBH)
    merger rate
  • Crucial especially for LISA event rate
  • Use n-body, Press-Schecter, merger trees
  • Measurement of high-z merger rate
  • (DEEP2)
  • Detection of binary MBHs
  • Galactic Dynamics the final parsec problem
  • Pulsar Timing Array

26
Conclusions
  • Massive Black Hole Binary coalescence rate
    depends on merger rate, Black Hole demographics,
    galactic dynamics
  • Major uncertainties in all of these, esp. at high
    z
  • µhz - nHz Newtonian regime potentially
    observable via Pulsar Timing
  • Final coalescence are brightest GW events
    observable via LISA
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