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Structure Formation in the Universe: The First Billion Years of Cosmic Evolution

This presentation by Naoki Yoshida from the National Astronomical Observatory discusses the early formation of structures in the universe during its first billion years. It explores significant concepts such as early reionization (~200 million years post-Big Bang), and the formation of Population III (PopIII) and Population II (PopII) stars. It delves into cosmological simulations, hydrodynamics, and the dynamics of early galaxies, with emphasis on the processes contributing to star formation and the role of primordial gas in the evolution of the universe.

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Structure Formation in the Universe: The First Billion Years of Cosmic Evolution

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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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