RHD Simulations on the Radiative Feedback from First StarsRHD Simulations on the Radiative Feedback...
Transcript of RHD Simulations on the Radiative Feedback from First StarsRHD Simulations on the Radiative Feedback...
![Page 1: RHD Simulations on the Radiative Feedback from First StarsRHD Simulations on the Radiative Feedback from First Stars Hajime Susa Rikkyo University, Japan. Seattle 2006, summer ...](https://reader030.fdocuments.us/reader030/viewer/2022041003/5ea6b6ea0155252411260f3a/html5/thumbnails/1.jpg)
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RHD Simulations on the Radiative Feedback
from First Stars
Hajime Susa Rikkyo University, Japan
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Radiative feedback
• H2 dissociation (Negative)– By nearby star– Background
• Ionization ( Positive & Negative )– Photoevaporation– Increase the catalysts for H2 formation– H2 shell formation
Abel et al 2006
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23/ 4
,0 14 -210 cmH
LW LWN
L L-æ ö÷ç= ÷ç ÷çè ø
( )2
126 2
20.88 10 ( )4LW
H eLn x T nrp
--= ´ equi l i br i um
( ) ( ) ( )11 23,03 3
4 24 -1 -1 3 -31kpc10 10 erg s Hz 10 K 1cm
LWesh
Lx T nr-- -
-
æ ö÷ç ÷ç= ÷ç ÷ç ÷ç ÷è ø
H2 photodissociation feedback in uniform gas cloud
Uniform low mass host clouds are totally Photodissociated by single POPIII star.
Omukai & Nishi 1999
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H2 photodissociation feedback on clumpy cloud
• Dynamically collapsing cloud ?• Photoionization?
Glover & Brand 20013 -3
crit 100pc@ 10 cmclumpD n »;
Dense clouds are able to survive the photodissociation feedback by another nearby star. dis fft t<
dis fft t>
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Numerical Methods
• Tree • SPH• RT of Ionizing photons by Ray Tracing• RT of Lyman-Werner photons by Ray Tracing
( Self-Shielding function)
• Implicit solver for reactions and energy equation• H2 (no He) • Everything parallelized utilizing MPI
( ) 22 2
3/ 414 2
14 2 if 1010
HLW sh H H
NF f N N cm
cm
--
-æ ö÷çµ = >÷ç ÷çè ø
H. Susa, PASJ 58, 445 (2006)
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First model of FIRST Cluster(Univ. of Tsukuba)
• 16 nodes (32 Xeon )• Gbit network• 16 Blade GRAPE
Blade-GRAPE
FIRST 16-node
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Setup
SPH particlesUniformly Distributed
48.3 10 M´3
clump 10cmn -=
3env 0.1cmn -=Uniform
dense clump
Run-away collapsing Core
pcD
(center)H onn n>
Turn on the nearby star
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Parameters524288SPHN =
Property of the Source Star
120M 49.92 10 K´4.6R
with/ without ionizing photons
2.5pc 140pcD = -
2 5 310 10 cmonn -= :
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Failed Collapse ( H2 fraction )3 -3
on 10 cm
40pc
n
D
=
= LW photons sweep the dense core and prevent the cloud from collapsing.
Core bounce
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Survived prestellar core (H2 fraction) 3 -3
on 10 cm
100pc
n
D
=
=
Collapsed core
H2 is self-shielded
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Time evolution of Central density
collapse
bounce
Turn-on
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Evolution of central density & tempetarute
Bounce
Thre
e di
ffer
ent i
nitia
l Tof
col
laps
ing
clou
d
We need some explanation
collapse
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Analytic argument (Susa 2006 in prep.)
• In the presence of strong LW intensity, H2 are in chemical equilibrium.
• H2 number density can be assessed with given density temperature, and LW flux.
• H2 cooling rate can be assessed with given density temperature, and LW flux.
• We can evaluate the cooling condition of the core by t_ff > t_cool (Condition like Rees & Ostriker )
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Ionized fraction is out of equilibrium
2 3/ 2323
pe erec e
Gmdy dy dt nk y ndn dt dn π
−= −
But we have analytic solution….
1 00 0
0
1
2( / 1)e
rece
ff
y ty n nt
−=
+ − Function of density
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H2 fraction in equilibrium
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Cooling condition
Once the collapsing core satisfy above condition, the collapse cannot be stopped.
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Bounce
RUN AWAY REGION
Susa, in preparation (2006)
D=20pc
collapse
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D=80pc
collapse
Bounce
RUN AWAY REGION
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Summary 1• We perform 3D RHD simulations for the radiative feedback effects on primordial star formation.
• Prestellar core could survive the LW flux, if the core density and temperature satisfy the cooling condition written by an analytic formula.
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Ionization + dissociationSusa & Umemura ApJL in press (2006)
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3 typical models
• Model A: non = 3x103 cm-3 , No ionizing photons (for comparison)
• Model B: non = 3x103 cm-3 , ionization• Model C: non = 3x102 cm-3 , ionization
• M*=120Msun , D=20 pc for all models
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Snap shots610-
y2H
yHIHn
T
810- 410-
410
410−
810−
1
Model A Model B Model C
T
Hn
yHIy
2H
410
410−
810−
1
THn
yHI
142H ,Ny
2H
10 200 10 200 10 200
142H ,N 142H ,N
Bounce collapse blown away
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Effects of ionizing photons
• Low density clump : – Photoheating– →Photoevaporation
• High density clump:– H2 shell formation– →Enhance the shielding of LW radiation– →collapse promoted
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Collapse criteria for core density-3
-3
-3
pc : cmpc : cmpc : cm
3
2
20 10
30 10
50 10
on
on
on
D n
D n
D n
=
=
=
t
t
t
If we consider non > 103 cm-3 ,(�tff < tpopIII) negative radiative feedback by nearby star is unlikely.
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Summary 2 • We perform 3D RHD simulations for theradiative feedback effects on primordial star formation.
• Ionization blow out the low density cloud (n < 10cc, if D=50pc).
• But it helps to form stars for dense clouds by H2 shell formation.
• Realistic density field as well as force of gravity by dark matter……… we need more simulations.
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FIRST
256 �16×16�nodes512 CPU �
256 Blade-GRAPE
512 Xeon : 2.9 Tflops
Blade-GRAPE: 8.7 Tflops
Memory: 512GB
Will be available in September, 2006