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S TRUCTURE F ORMATION IN THE U NIVERSE - THE FIRST ONE BILLION YEARS -

S TRUCTURE F ORMATION IN THE U NIVERSE - THE FIRST ONE BILLION YEARS -. Naoki Yoshida National Astronomical Observatory. Niigata 3/12/2003. WMAP first year results. Early reionization （ ~200 million years ）. Reionization sources. 1 What are they ? PopIII stars /

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S TRUCTURE F ORMATION IN THE U NIVERSE - THE FIRST ONE BILLION YEARS -

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  1. STRUCTURE FORMATION IN THE UNIVERSE- THE FIRST ONE BILLION YEARS - Naoki Yoshida National Astronomical Observatory Niigata 3/12/2003

  2. WMAP first year results Early reionization （~200 million years）

  3. Reionization sources • 1 What are they ? • PopIII stars/ • ordinary (PopII) stars? • 2 Whendid they form ? • z > 20. Mostlyz > 10 ? • 3 Where? • in mini-halos/galaxies? • 4 How abundant? • 1/2/3 - s peaks ?

  4. z = 14 z = 22 ~100 Myrs 1st generation 2nd generation 6 7 10 Msun 7x10 Msun

  5. Cosmological Simulations of theFirst Generation Objects Matter density fluctuations (CDM + baryons+ CMB photons) Gravity Hydrodynamics Chemical reactions Gas H2 N-body Euler equation Primordial 9 species Non-equilibrium treatment e, H, H+, H-, H2, H2+, He, He+, He++ z = 100

  6. Chemical reactions e, H, H+, H-, H2, H2+, He, He+, He++ Primordial gas : 76% hydrogen, 24% helium • Collisional processes, recombinations • Formation of H2( H + e g H + hn; H + H g H2 + e ) • Photo-ionization, dissociation (UV background) • Radiative cooling： • collisional excitation,ionization, recombination, • inverse-Compton • Molecular hydrogen ro-vibrational lines(Galli & Palla 1998) - - 31 reactions

  7. Very Early Structure Formation Density distributions for baryons and dark matter Gas DM Gas Dark matter Gas H2 z=50 z=100 z=30 z=25 H2 Gas 500 kpc The first baryonic object !

  8. Early star-forming gas clouds z=17 1 Mpc 60million particles 100Msun per gas particle

  9. Three important things: • Characteristic mass of the first objects • Complex dynamical effect (galaxy clusters at z=0  First objects) • Radiative feedback

  10. Characteristic mass of the first objects 6 M_host ~ 10 Msun Yoshida, Abel, Hernquist, Sugiyama (2003a)

  11. Simpler picture… Galaxy formation (20th century) “There’s a halo, yes! it’s a galaxy.” + H He Early gas clouds z=25: H2 t_dyn ~ 30 Myrs t_cool ~ 30 Myrs t_chem ~ 30 Myrs t_hubble ~ 100 Myrs

  12. Formation of CDM halos (5%)

  13. FIRST LIGHT Stars in molecular gas clouds HII regions + soft UV

  14. “Fragile” hydrogen molecules -23 -1 -2 -1 -1 J=10 erg sec cm Hz str (11.18 – 13.6 eV) Self-shielding against soft-UV radiation No radiation core Substantial modulation due to large H2 columns in large halos (>> 10 cm ) Equilibrium abundance 14 2

  15. Furthermore: 1 Lyman-series absorption by “abundant” neutral hydrogen 2 Cosmological redshift (~11% increase in expansion parameter) 3 It is essentially a line-transfer problem in 3D with a complex gas velocity field (c.f. stationary gas in 1D case studied by Ricotti et al. 2001) First star  soft UV  no more H2 cooling ?

  16. Simulation of Early Reionization Chemo-hydro cosmological simulation Jeans-unstable gas clouds Massive PopIII star in the gas clouds + semi-analytic treatment of internal and external feedback Adaptive ray-tracing to track the propagation of I-fronts (Sokasian 2003)

  17. Evolution of ionization front Sokasian, Yoshida, Abel, Hernquist (2003) LCDM model 300 Msun Population III star per gas cloud z=24 z=22 neutral ionized z=20 z=18

  18. Star Formation Rate

  19. Only one star per star-forming region Ionized Volume Fraction

  20. Thomson Optical Depth Sokasian, Yoshida, Abel, Hernquist (2003)

  21. Theoretical Studies on Cosmic Reionization Gnedin & Ostriker (1997-2000), Sokasian et al. (2003) -- Conventional picture z~7 (small box), too low optical depth Ricotti et al. (2002) -- Small box. Resolution (~10^4 Msun) not enough for early objects. Nakamoto & Umemura (2000) -- Conventional picture z~7. Radiative transfer. (perhaps) too low optical depth Yoshida et al. (2003a,b,c,d) -- Small box size, high-res. (10^2-10^3 Msun), somewhat exotic massive PopIII Ciardi, Ferrara & White (2003) -- Low-res. (10 Msun) DM simulation + SA gal.form. No hydro.  gas clumping uncertain Cen(2003), Loeb et al. (2003), Fukugita & Kawasaki (2003), Haiman & Holder (2003) -- Press-Schechter. Many ingredients uncertain (C_clump, f_esc, c_star) (most notably gas clumping) Madau et al. (2003) Haiman, Abel, Rees (2000) -- Early quasars. Semi-analytic. Accretion efficiency onto BHs uncertain. 9

  22. Suggestions: • Correct gas clumping using hydrodynamic simulations (or clever idea) • A factor of 10 miss-estimate of gas clumping is similar • to a factor of 10 enhanced photon production (t_desired !) • Escape fraction from proto-galaxies • ~100% for mini-halos (Kitayama 2003), but ??? for the first galaxies • again, a factor of 2 … • Formation of early generation stars, • instead of “THE” very first star • Are all the first stars massive as ABN and Omukai suggest ? • Population III likely unimportant in photon-production, • but not negligible (even very important) in terms of IGM clumping • and subsequent gas cooling in larger halos • Formation of dense gas clouds in proto-galaxies • First disk galaxies

  23. -21 -1 -2 -1 -1 J=10 erg sec cm Hz str (100,000 K thermal) Pre-heating at z=20

  24. A Hubble time (~ 2 dynamical times) later : Gas DM

  25. THERMODYNAMIC EVOLUTION before reionization after (brief) reionization 20 Myr after 50 Myr 100 Myr

  26. CHEMICAL EVOLUTION 1st object 2nd generation object H2 cooling plays a role in both cases!

  27. FIRST STARS AS AN ORIGIN OFHEAVY ELEMENTS

  28. Metals at high-z • CIV at z~5(Songaila 2001, constant at z=3-5) • Damped Lyman-a systems at z=3-5 (Prochaska 2002) • FeII emission from z=6 quasars (Freudling, Corbin, Korista 2003) • Silicon in intra-cluster medium(abundance anomaly) (Baumgartner et al.2003) • Blackholes （Inoue & Chiba 2003；　Merritt & Ferarrese 2001)

  29. Where did they come from…? Massive Population III stars （１００－３００Msun）

  30. ６４ A 200 Msun star⇒　３ｘ１０　　 UV photons N Z －６ ζ==　５ｘ１０ Nγ Massive Population III stars: １．Very luminous ２．Efficient metal factory 3. Powerful metal distributor （Early reionization inferred from the WMAP data） A 200 Msun star⇒ ~９０Msun helium core

  31. The death of the first stars (Bromm, Yoshida & Hernquist 2003) 6 M ~ 10 Msun 1 kpc

  32. The first supernova explosion 53 Esn ~ 10 ergs (PISN, Hypernovae) 1kpc Remnant cools by Inverse Compton  SZ sources!

  33. N Z －６ ζ==　５ｘ１０ Nγ Star formation history in the early universe Initial density fluctuations Formation of halos Gas heating/cooling Molecular gas cloud formation Massive stars analytic model Nbody/hydro+RT Ｚ

  34. -8 -8 Ω Ω ～ 3 x 10 ～ 10 CIV CIV -5 Ω ～ 10 PopIII necessaryexpected Thomson optical depth High-z IGM Cluster ICM Δτ~ 0.06 Δτ ~ 0.05 PopIII (Songaila 2001) -7 Ω ～ 5 x 10 PopIII (Baumgartner et al. 2003)

  35. Prospects for observation SKA NGST ~nJy sensitive NIR instrument LOFAR Direct imaging 21 cm emission H2 lines Infrared-missions (Ha/HeII lines) High-z GRBs (afterglow) Planck satellite (not only t)

  36. BRIGHT FUTURE FOR Cosmology on small scales

  37. イオン化波面の伝播 Adaptive Ray Casting Scheme Ri+1 dt Ri ne,np N

  38. イオン化領域の割合 モデル : • ガス雲につき一つのPopIII星 • f_esc = 1 • イオン化領域では星形成なし

  39. Thomson optical depth WMAP TE detection （原始）銀河で できた星 CDM WDM Pop II only 赤方偏移

  40. Metal yield of a PopIII star Heger & Woosley (2002)

  41. Prospects for observations • Determination of reionization history (not only t) by post-WMAP CMB experiment, • by observations of GRB afterglows • (see poster by Ioka). • 2. Huge Lyman-a forests sample from SDSS • as well as gal.-gal. power spectrum. • 3. Observations of galactic lens systems • (Metcalf et al. 2003; Dalal & Kochanek 2003).

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