FIRST Project:

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FIRST Project Formation and Feedback of First
Stars
Masayuki Umemura Univ. of Tsukuba, Japan
Collaborators H. Susa (U Kounan) T. Suwa (U
Tsukuba) D. Sato (U Tsukuba) FIRST Project team
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Contents
1. What is the FIRST project 2. 3D SPH
simulations on first star formation 3. 3D RHD
simulations on radiative feedback 4. Conclusions
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Project
20042007 by MEXT Total budget is 428 million yen
(US3.6 million)
Fusional Integrator for Radiation-hydrodynamic
Systems in Tsukuba University for elucidating
FIRST generation objects
A hybrid computer system dedicated for
calculations of first objects
Large radiation hydrodynamic simulations
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Blade-GRAPE X64
(A new type of GRAPE)
Direct summation of self-gravity 4 GRAPE6 chips
136.8GFLOPS Memory of 16MB (260 thousand
particles)
GRAPE6 chips 4
Blade-GRAPE
heat-sink
Cooperation Hamamatsu Metrics Co. KF Computing
Research Co.
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FIRST Simulator
Completed in March, 2007
2-15 th
256 (1616) nodes 496 CPU 16 Blade-GRAPE
224 Blade-GRAPE X64 Total Performance 36.1
Tflops Host 3.1 Tflops Blade-GRAPE 33
Tflops Total Memory 1.6TB Total storage
22TB (Gfarm)
1st model
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P3M-GRAPE-SPH Simulations(Poster by Suwa et al.)
WMAP 3 year ?CDM cosmology
zin15, 100kpc comoving3
Baryon mass 6?106M? Dark matter mass 3?107M?
4 x 107 particles for baryon dark matter
Mass resolution 0.3M? in baryon
1.5M? in DM No change of mass
resolution throughout the simulation
a highest peak
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Stage 1 Nonlinear Growth to Form a Runaway Core
kpc (comoving)
Hanawa Matsumoto (2000) A collapsing gas
sphere is unstable against bar mode, if
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Stage 2 Asymmetric Runaway
kpc (comoving)
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Stage 3 Fragmentation
kpc (comoving)
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Two Fragmentation Modes
Nakamura Umemura, 2001, ApJ, 548, 19
1) Fragmentation at the critical density of H2
2) Opacity limited fragmentation at n?1012cm-3
Rees mass
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Pre-fragmentation
Post-fragmentation
peak2
peak1
Density profile
Density profile
cm-3
cm-3
green x-axis red y-axis
106
105
green x-axis (peak1) red y-axis (peak1) blue
x-axis (peak2) pink y-axis (peak2)
Fragments are still asymmetric
Mass profile
Mass profile
M?
M?
103
103
100
100
10
10
red peak1 blue peak2
1
1
10-4
0.1
10-4
0.1
kpc (comoving)
kpc (comoving)
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Dark Matter Contribution
Pre-fragmentation
Post-fragmentation
M?
M?
total
total
dark matter
dark matter
baryon
baryon
10-5
0.1
10-5
0.1
kpc (comoving)
kpc (comoving)
Dark matter contribution is less than 10.
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Angular Momentum Distribution
Pre-fragmentation
Post-fragmentation
fr
fr
pc km s-1
pc km s-1
specific angular momentum
specific angular momentum
log M
log M
(Yoshida et al 2006)
Rotation energy is 10 of gravitational energy.
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Pre-fragmentation
Thermal History
T
Post-fragmentation
n
T
n
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Radiative Feedback from Pop III Star
Negative ? or Positive ?
Key Physics (Reviews by M. Norman, B.
Ciardi) ?Photoheating ?H2 molecule formation by
ionization ?Photo-dissociation of H2 molecules
(Solomon process by Lyman-Werner band) ?
Propagation of ionization front
(R-,M-,D-type)
? Radiation Hydrodynamics Hydrodynamics
coupled with radiation transfer and
non-equilibrium chemistry
?100pc
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Ionization Front
Kahn 1954
IF
HII
HI
Photon conservation
solution for
IF
R-type
supersonic
IF
D-type
subsonic
IF
shock
M-type
supersonic
subsonic
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Coupling with Gravitational Instability
Runaway collapsing core
n
R
D
UV
R-type IF
R-type ionization front propagates always before
gravitational collapse ? Evaporation by
photoheating
D-type IF
Gravitational collapse occurs before D-type
ionization front propagates ? No evaporation
by photoheating
M-type IF
Not clear
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TREE-GRAPE-SPH Radiative transfer
Non-equilibrium Chemistry Thermal processes
RSPH Scheme for 3D Radiation Hydrodynamics
Susa (2006)
1. Hydrodynamics SPH (Umemura 1993 Steinmetz
Muller 1993)
2. Self-gravity Parallel Tree-GRAPE code
(Orthogonal Recursive Bisection )
3. Frequency-dependent Radiative Transfer
(Ray-tracing) (Kessel-Deynet Burkert 2000,
Nakamoto et al. 2001)
4. Non-equilibrium Chemistry Thermal Processes
(Susa Kitayama 2000)
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H2 Shielded Collapse
Susa Umemura 2006
M-type IF
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H2 Shielded Collapse
? A shock is raised by M-type IF ? H2 shell
shields LW radiation ? Core collapse is faster
than shock propagation
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Shock-driven Evaporation
? shock is raised by M-type IF ? shock blows
the collapsing core
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Shock-driven Evaporation
? A shock is raised by M-type IF ? A shock blows
the collapsing core
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Threshold density
? collapse evaporation
Pop III region
M-type IF
R-type IF
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Radiative Feedback on Peaks
(Poster by Sato et al.)
120M?
All peaks continue to collapse.
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Summary
? Fragmentation can occur in asymmetric runaway
collapse. A question is under which condition a
runaway core fragments. A key might be the
elongation triggered by DM fluctuations in an
early stage. ( gt 108 SPH simulations are
on-going, using FIRST simulator. ) ? Radiative
feedback from a first star is mostly positive
through the shielding of LW band photons due to
the enhanced H2 molecule ahead of ionization
front. As a result, the formation of multiple
stars is possible in a halo.