Document

Radiative Feedback
on the formation of
first generation subgalactic objects
Hajime Susa
Rikkyo University
First Generation Objects
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Predicted by CDM density Perturbation
Theory @10<z<30.
M>10^6 M_sun (Tvir>10^3 K)
Cooled by H2 lines and H-Lyα
Cooling Diagram (RO +H2)
3s
2s Cluster of Gals.
1s
Large Gals.
dwarf Gals ?
First Generation Objs.
1
2
3
4
5
6 7 8 9
10
1+ zvir
2
3
4
5
6 7 8 9
100
Cooling by H atom
Cooling by H2
First Generation
Subgalactic Objects
Nishi & Susa 1999
Substructure in Galactic Halo
Cluster Halo
5  1014 M
Galactic Halo
2  1012 M
Moore et al. 1999
20 times smaller than expected
Feedback
Cooling diagram of primordial gas
& SN disruption
100SN
Nishi & Susa（1999）
Primodial Virialized Gas
10SN
Cooling＋SN disruption
1SN
M  10 M halos
8
merginally survive 100 SN
SN (Simulation)
Wada & Venkatesan 2003
z=10, 10^8 M_sun
1000 SN/Myr →disruption
100 SN/Myr →collapse induced
SN feedback
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10^8 M_sun halos @z=10 seems to be
difficult to be destroyed soley by SN.
But more simulations are required to assess
the effects of SN feedback…
Impacts of UVB on GF
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PHOTOIONIZATION
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PHOTODISSOCOATION
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Production of electrons : catalysts of H2 formation →
enhance the fraction of H2
Enhance the Compton cooling rate
Dissociation of H2 → No coolant
PHOTOHEATING
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Keep the gas temperature 104-105 K
Photo-evaporation
Suppression of SF in gals.
Cooling and heating rates
Equilibrium temperature
is 104-105K
Dynamics of Galaxies
with Tvir < 104 K
are strongly affected.
Photoevaporation
Thoul & Weinberg 1996
Late Reionization, CDM density
perturbation, and Radiative cooling.....
If Z_reion=6, 1σ density
perturbations are not
prevented from forming
stars.
Blown away
by photo-evaporation
7
Early reionization (WMAP)
Spergel et al. 2003
 (zrec )  0.17  0.04
Instantaneous reionization:
zreion  17  3
Early Reionization, CDM density
perturbation, and Radiative cooling.....
If Z_reion=20, >2σ
density perturbations are
prevented from forming
stars.
Shaded ≒ Blown away
by photo-evaporation
20
Smaller scale sub-clumps

x
In hierarchical clustering scenario, small clumps
evolve faster than the parent system.
Method (RSPH)
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SPH
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Gravity
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HMCS in University of Tsukuba (CCP)
GRAPE6, direct-sum
Radiation transfer of ionizing photons
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Steinmetz & Muller 1993
Umemura 1993
Kessel-Dynet & Burkurt 2000
Nakamoto, Umemura & Susa 2001
Primordial chemistry & Cooling
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Susa & Kitayama 2000
Galli & Palla 1998
Model of SF
1.T  5000 K
In order to evaluate the case of
maximal star formation rate, we assume
2. y H 2  5  104

3.
 200

4.   v  0

d * c* gas

,
dt
t ff
c*  1
Model of UVB
I 21
I 21
1  z  / 3 3
I 21 exp 12  3z 
1
I 21 0.01exp  3(17  z) 
I 21 0.01
3
5
1 z
Put a source outside the simulation box so that the
mean intensity is equal to above value at the center.
18
Minimally Required I21
yHI  103 ,   5
y HI  103 ,   1
yHI  0.1,   5
yHI  0.1,   1
再結合＝光電離
I L  n 0 (1  z ) krec
3
(1  y HI )2 hpl
3   
y HI
4s L
Typical Result (M=107Msun,Zc=10)
300pc
Maximally Star-forming model
2s
3
3s
2
M
 100
L
Vc=20 km/s
6
5
4
“ Evaporated ”
3
Vc=10 km/s
2
M d 108 M or
7
6
5
4
vrot d 20km/s
1s
3
Vc=5 km/s
2
6
>95% halos are
photo-evaporated.
6
5
4
3
6
7
8
9
10
2
Convergence
(# of particles and Softening )
N  217
N  215
N  217
N  215
N  214
N  213
N  214
N  213
Substructure in Galactic Halo
Cluster Halo
5  1014 M
Galactic Halo
2  1012 M
Moore et al. 1999
20 times smaller than expected
Kravtsov et al. (2004)
～10% of halos with 10^8-10^9 M_sun halos are much more massive in the past.
Evidences of invisible substructures
by gravitational lensing
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Chiba (2002)
Dalal & Kochanek (2002)
Consistent with the CDM N-body simulations
Internal radiative feedback
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Kitayama, Yoshida, Susa, Umemura 2004
single POPIII star at the center of the cloud
ガスの消失
ガスは失われず
ガスはほぼ完全に消失
ただしガスは星が消えると10^7 yrくらいかけて戻ってくる。
原始組成からできる星の質量
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本当のFirst Stars → Very Massive ?
再電離を生き残るT_vir＞10^4 K くらいの雲→
電離度高
電離度高→H2が多量にできる
H2が多量にできるとHDが多量にできる⇒温度
が下がって分裂の質量が少し100Msunよりだい
ぶ小さくなる(F.Nakamura)。
水素分子の過剰生成
Susa et al. 1998
衝撃波の後面で再結合
の遅れ
およそ50km/s以上の
衝撃波では水素分子量
がa few ×10^{-3}程度
数万度以上の
ビリアル温度を持つ雲では
この過程が起きる。
Fragment mass
Nakamura & Umemura 2002
Summary
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3D RHD の方法で早期再電離のモデルの計算を
行った。
20km/s以下のビリアル温度を持つ天体の形成は、
早期再電離モデルでは著しく阻害される。
内部のPOPIII星からのradiative feedbackの影響も
大きく、10^7Msun以下の天体は電離による加熱で
ガスを失う。
したがって星団としての銀河が誕生するのはビリア
ル温度が10^4K以上の天体と考えられるが、それら
の天体ではたとえメタルがほとんどなくても星の質量
は少し下がる可能性がある。

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