STRUCTURE FORMATION IN THE

UNIVERSE- THE FIRST ONE BILLION YEARS -

Niigata 3/12/2003

Naoki YoshidaNational Astronomical Observatory

WMAP first year results

Early reionization（ ~200 million years ）

Reionization Reionization sourcessources

1 What are they ? PopIII stars / ordinary (PopII) stars ?

2 When did they form ? z > 20. Mostly z > 10 ?

3 Where ? in mini-halos/galaxies ?

4 How abundant ? 1/2/3 - peaks ?

1st generation 2nd generation

z = 22 z = 14~100 Myrs

10 Msun 7x10 Msun6 7

Cosmological Simulations of theCosmological Simulations of theFirst Generation ObjectsFirst Generation Objects

Gas H2

Primordial 9 species Non-equilibrium treatmente, H, H+, H-, H2, H2+, He, He+, He++

Matter density fluctuations (CDM + baryons + CMB photons)

Gravity Hydrodynamics

Chemical reactions

z = 100

N-body

Euler equation

• Collisional processes, recombinations

• Formation of H2 ( H + e H + h; H + H H2 + e )

• Photo-ionization, dissociation (UV background)

• Radiative cooling ： collisional excitation, ionization, recombination, inverse-Compton Molecular hydrogen ro-vibrational lines (Galli & Palla 1998)

Chemical reactionsChemical reactionse, H, H+, H-, H2, H2+, He, He+, He++

31 reactions

- -

Primordial gas : 76% hydrogen, 24% helium

Very Early Structure Very Early Structure FormationFormation

Gas H2

Gas H2

Gas Dark matter

z=25

z=50

Gas DM

The first baryonic object !

Density distributions for baryons and dark matter

500 kpc

z=100

z=30

Early star-forming gas cloudsEarly star-forming gas clouds

1 Mpc

z=17

60million particles

100Msun pergas particle

Three important things:Three important things:

Characteristic mass of the first objectsCharacteristic mass of the first objects

Complex dynamical effectComplex dynamical effect

(galaxy clusters at z=0 (galaxy clusters at z=0 First First objects)objects)

Radiative feedbackRadiative feedback

Characteristic mass of the first Characteristic mass of the first objectsobjects

M_host ~ 10 Msun6

Yoshida, Abel, Hernquist, Sugiyama (2003a)

Simpler picture…

H He

H2

+

t_dyn ~ 30 Myrst_cool ~ 30 Myrst_chem ~ 30 Myrst_hubble ~ 100 Myrs

z=25:

Galaxy formation (20th century)“There’s a halo, yes! it’s a galaxy.”

Early gas clouds

Formation of CDM halos (5%)

Stars in molecular gas clouds HII regions + soft UV

““Fragile” hydrogen Fragile” hydrogen molecules molecules

J=10 erg sec cm Hz str (11.18 – 13.6 eV)

-23 -1 -2 -1 -1

Self-shielding againstsoft-UV radiation

Equilibrium abundance

No radiation

Substantial modulationdue to large H2 columnsin large halos (>> 10 cm )

core

14 2

Furthermore:

1 Lyman-series absorption by 1 Lyman-series absorption by “ “abundant” neutral hydrogenabundant” neutral hydrogen

2 Cosmological redshift2 Cosmological redshift (~11% increase in expansion parameter)(~11% increase in expansion parameter)

3 It is essentially a line-transfer problem in 3 It is essentially a line-transfer problem in 3D 3D

with a complex gas velocity fieldwith a complex gas velocity field (c.f. stationary gas in 1D case studied (c.f. stationary gas in 1D case studied by Ricotti et al. 2001)by Ricotti et al. 2001)

First star soft UV no more H2 cooling ?

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)

Evolution of ionization front

z=24 z=22

z=20 z=18

Sokasian, Yoshida, Abel, Hernquist (2003)

300 Msun Population III starper gas cloud

neutral

ionized

CDM model

Star Formation RateStar Formation Rate

Ionized Volume FractionIonized Volume Fraction

Only one star per star-forming region

Thomson Optical DepthThomson Optical Depth

Sokasian, Yoshida, Abel, Hernquist (2003)

Theoretical Studies on Cosmic Theoretical Studies on Cosmic ReionizationReionizationGnedin & Ostriker (1997-2000), Sokasian et al. (2003) Gnedin & Ostriker (1997-2000), Sokasian et al. (2003) -- Conventional picture z~7 (small box), too low optical depth-- Conventional picture z~7 (small box), too low optical depth

Ricotti et al. (2002)Ricotti et al. (2002) -- Small box. Resolution (~10^4 Msun) not enough for early objects.-- Small box. Resolution (~10^4 Msun) not enough for early objects.

Nakamoto & Umemura (2000)Nakamoto & Umemura (2000) -- Conventional picture z~7. Radiative transfer. (perhaps) too low optical depth-- Conventional picture z~7. Radiative transfer. (perhaps) too low optical depth

Yoshida et al. (2003a,b,c,d) Yoshida et al. (2003a,b,c,d) -- Small box size, high-res. (10^2-10^3 Msun), somewhat exotic massive PopIII -- Small box size, high-res. (10^2-10^3 Msun), somewhat exotic massive PopIII

Ciardi, Ferrara & White (2003)Ciardi, Ferrara & White (2003)-- Low-res. (10 Msun) DM simulation + SA gal.form. -- Low-res. (10 Msun) DM simulation + SA gal.form. No hydro. No hydro. gas clumping uncertain gas clumping uncertain

Cen(2003), Loeb et al. (2003), Fukugita & Kawasaki (2003), Haiman & Holder (2003)Cen(2003), Loeb et al. (2003), Fukugita & Kawasaki (2003), Haiman & Holder (2003) -- Press-Schechter. Many ingredients uncertain (C_clump, f_esc, c_star)-- Press-Schechter. Many ingredients uncertain (C_clump, f_esc, c_star) (most notably gas clumping)(most notably gas clumping)

Madau et al. (2003) Haiman, Abel, Rees (2000)Madau et al. (2003) Haiman, Abel, Rees (2000)-- Early quasars. Semi-analytic. Accretion efficiency onto BHs uncertain.-- Early quasars. Semi-analytic. Accretion efficiency onto BHs uncertain.

9

Suggestions: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 (_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 clumpingand subsequent gas cooling in larger halos

Formation of dense gas clouds in proto-galaxies- First disk galaxies

Pre-heating at z=20Pre-heating at z=20

J=10 erg sec cm Hz str (100,000 K thermal)

-21 -1 -2 -1 -1

A Hubble time (~ 2 dynamical times) A Hubble time (~ 2 dynamical times) later :later :

Gas DM

THERMODYNAMIC EVOLUTION

20 Myr after 50 Myr 100 Myr

before reionization

after (brief) reionization

CHEMICAL EVOLUTION

1st object 2nd generation object

H2 cooling plays a role in both cases!

FIRST STARS AS AN ORIGIN FIRST STARS AS AN ORIGIN OFOF

HEAVY ELEMENTSHEAVY ELEMENTS

Metals at high-zMetals at high-z CCIVIV at z~5 at z~5 (Songaila 2001, constant at z=3-5)(Songaila 2001, constant at z=3-5)

Damped Lyman-Damped Lyman- systems at z=3-5 systems at z=3-5 (Prochaska 2002)(Prochaska 2002)

FeFeIIII emission from z=6 quasars emission from z=6 quasars (Freudling, Corbin, Korista 2003)(Freudling, Corbin, Korista 2003)

Silicon in intra-cluster mediumSilicon in intra-cluster medium (abundance (abundance anomaly)anomaly)

(Baumgartner et al.(Baumgartner et al. 2003)2003)

BlackholesBlackholes （（ Inoue & Chiba 2003Inoue & Chiba 2003 ；　；　 Merritt & Ferarrese Merritt & Ferarrese

2001) 2001)

Where did they come from…?

Massive Population III stars（１００－３００ Msun ）

Massive Population III stars:Massive Population III stars:１． Very luminous

２． Efficient metal factory

3. Powerful metal distributor

A 200 Msun star ⇒　３ｘ１０　　 UV photons６４

（ Early reionization inferred from the WMAP data ）

A 200 Msun star ⇒ ~ ９０ Msun helium core

ζ= = 　５ｘ１０Nγ

N Z －６

The death of the first stars(Bromm, Yoshida & Hernquist 2003)

M ~ 10 Msun6

1 kpc

The first supernova The first supernova explosionexplosion

Esn ~ 10 ergs(PISN, Hypernovae)

53

1kpc

Remnant cools byInverse Compton SZ sources!

Initial density fluctuations

Formation of halos

Gas heating/cooling

Molecular gas cloudformation

Massive stars

Ｚ

analytic model

Nbody/hydro+RT

ζ= = 　５ｘ１０Nγ

N Z －６

Star formation history in the early Star formation history in the early universeuniverse

necessarynecessary 　　　　　　　　　　　　expectedexpected

Thomson optical depth

High-z IGM

Cluster ICM

Δτ ~ 0.05

ΩCIV ～ 3 x 10-8

ΩPopIII～ 10 -5

Δτ~ 0.06

ΩCIV ～ 10-8

ΩPopIII～ 5 x 10 -7

(Songaila 2001)

(Baumgartner et al. 2003)

PopIII

Prospects for observation

~nJy sensitive NIR instrument

Direct imaging21 cm emissionH2 linesInfrared-missions (H/HeII lines)High-z GRBs (afterglow)Planck satellite (not only )

BRIGHT FUTURE FOR

イオン化波面の伝播

Adaptive RayCastingScheme

N

ne,np

Ri

Ri+1

dt

モデル :

1. ガス雲につき一つの PopIII 星 2. f_esc = 13. イオン化領域では星形成なし

イオン化領域の割合

Thomson optical depthWMAP TE detection

CDM

Pop II only

WDM

dzdz

dtcn

z

eT

（原始）銀河でできた星

赤方偏移

Metal yield of a PopIII starMetal yield of a PopIII star

Heger & Woosley (2002)

Prospects for observations Prospects for observations

1. Determination of reionization history (not only ) by post-WMAP CMB experiment,

by observations of GRB afterglows (see poster by Ioka).

2. Huge Lyman- forests sample from SDSS as well as gal.-gal. power spectrum.

3. Observations of galactic lens systems (Metcalf et al. 2003; Dalal & Kochanek

2003).