Hajime Susa Rikkyo University

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1 Hajime Susa Rikkyo University
Radiative Feedback on the formation of first generation subgalactic objects Hajime Susa Rikkyo University

2 First Generation Objects
Predicted by CDM density Perturbation M>10^6 M_sun (Tvir>10^3 K) Cooled by H2 lines and H-Lyα

3 Cooling Diagram (RO +H2)
3s Cluster of Gals. 2s 1s Large Gals. dwarf Gals ? First Generation Objs. 2 3 4 5 6 7 8 9 2 3 4 5 6 7 8 9 1 10 100

4 Cooling by H atom Cooling by H2 First Generation Subgalactic Objects
Nishi & Susa 1999

5 Substructure in Galactic Halo
Cluster Halo Moore et al. 1999 Galactic Halo 20 times smaller than expected

6 Feedback

7 Cooling diagram of primordial gas & SN disruption
Nishi & Susa（1999） Primodial Virialized Gas Cooling＋SN disruption 10SN 1SN

8 SN (Simulation) Wada & Venkatesan 2003 z=10, 10^8 M_sun
1000 SN/Myr →disruption 100 SN/Myr →collapse induced

9 SN feedback 10^8 M_sun seems to be difficult to be destroyed soley by SN. But more simulations are required to assess the effects of SN feedback…

10 Impacts of UVB on GF PHOTOIONIZATION PHOTODISSOCOATION PHOTOHEATING
Production of electrons : catalysts of H2 formation → enhance the fraction of H2 Enhance the Compton cooling rate PHOTODISSOCOATION Dissociation of H2 → No coolant PHOTOHEATING Keep the gas temperature K Photo-evaporation Suppression of SF in gals.

11 Cooling and heating rates
Equilibrium temperature is K Dynamics of Galaxies with Tvir < 104 K are strongly affected. Photoevaporation Thoul & Weinberg 1996

12 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

13 Early reionization (WMAP)
Spergel et al. 2003 Instantaneous reionization:

14 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

15 Smaller scale sub-clumps
In hierarchical clustering scenario, small clumps evolve faster than the parent system. ３D！

16 Method (RSPH) SPH Gravity Radiation transfer of ionizing photons
Steinmetz & Muller 1993 Umemura 1993 Gravity HMCS in University of Tsukuba (CCP) GRAPE6, direct-sum Radiation transfer of ionizing photons Kessel-Dynet & Burkurt 2000 Nakamoto, Umemura & Susa 2001 Primordial chemistry & Cooling Susa & Kitayama 2000 Galli & Palla 1998

17 Model of SF In order to evaluate the case of
maximal star formation rate, we assume

18 Model of UVB Put a source outside the simulation box so that the
mean intensity is equal to above value at the center.

19 Minimally Required I21 再結合＝光電離

20 Typical Result (M=107Msun,Zc=10)
300pc

21 Maximally Star-forming model
3 4 5 6 2 7 8 9 10 2s 3s Vc=20 km/s “ Evaporated ” Vc=10 km/s 1s Vc=5 km/s >95% halos are photo-evaporated.

22 Convergence (# of particles and Softening )

23 Substructure in Galactic Halo
Cluster Halo Moore et al. 1999 Galactic Halo 20 times smaller than expected

24 Kravtsov et al. (2004) ～10% of halos with 10^8-10^9 M_sun halos are much more massive in the past.

25 Evidences of invisible substructures by gravitational lensing
Chiba (2002) Dalal & Kochanek (2002) Consistent with the CDM N-body simulations

26 Internal radiative feedback
Kitayama, Yoshida, Susa, Umemura 2004 single POPIII star at the center of the cloud

27 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。

28 原始組成からできる星の質量 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)。　

29 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。

30 Fragment mass Nakamura & Umemura 2002

31 Summary 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。