The first sources of light in the Early Universe and the highest plausible redshift of luminous Quasars

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The first sources of light in the Early Universe
and the highest plausible redshiftof luminous
Quasars

• Andreas Müller
• Landessternwarte Heidelberg
• Oberseminar 2001
• Entstehung von Quasaren

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Overview
The Cosmological Setup
Primordial Objects
Cosmological Ingredients
The Lya Forest
Reionization
zreion measurements
Gnedin Simulations
Reionization Tools
Future Instruments Challenges
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A flat LCDM Universe

• Gamov 1948 hypothesis of CBR afterglow
• 3K-radiation isotropic (Penzias Wilson 1964)
• a Big Bang relic
• COBE data reveal fluctuations in CMB in mK domain
• Large scale CMB temperature anisotropy
• a confirmed by new instruments with higher
• resolution (x 30) balloon experiments
• BOOMERANG, MAXIMA
• a Detection of seed clumps for galaxy formation
• results flat universe with LCDM cosmology
• L gt 0 WL 0.62
• WB 0.05 WCDM 0.33
• WHDM 0.001 (n) Wtot 1.0
• inflation compatible

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Milestones in the history of the Universe
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Fragmentation of Primordial Objects

• Collapsing DM mini halos at z 30
• SPH simulations
• Initial mass 2 x 106 M8
• Cooling via H2 chemistry from Tgas 104 K
• to the CMB floor of 86 K
• Fragmentation to high-density clumps
• (n gt 108 cm-3)
• Clump growing by gas accretion and merging
• to 104 M8 clumps
• a first PopIII stars rather massive!
• Recently metallicity effects included
• gas with higher metallicities settles into
• center of DM halos!
• need pre-enrichment event for Z 10-3Z8

Bromm et al. 2001
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Gas-Clump Morphology at z 28
30 pc
Bromm et al. 2001
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The high-mass Progenitors Protogalactic DM
Clumps
18 small blue objects collisions and merging Ä
each in 4 Gpc distance growing Ä
each several billion stars hierarchical structure
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The Hierarchical Structure

• z 30 1st generation of stars and quasars
• Reionization of most H in the universe at z 7
• Current observations at threshold for probing
• H reionization epoch!
• Tool observational study of HZ sources
• CMB anisotropies small density fluctuations
• a large-scale structure of the universe (LSS)
• Gravitational collapses in dense regions a clumpy
  structure
• Constraint by observations evolution of galaxies
  at z lt 6
• Elementary building blocks 1st gaseous objects
  with Jeans mass ( 104 M8) a formed in SCDM
  models at z 15-30
• Evolution of the Universe
• homogeneous, isotropic, simple a clumpy,
  complicated

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The Cosmological Ingredients and Numerics

• Simple setup
• i) primordial power spectrum of Gaussian
  density fluctuations
• ii) DM mean density
• iii) initial temperature and density of cosmic
  gas
• iv) primordial composition by Big Bang
  nucleosynthesis
• v) lack of dynamically-significant magnetic
  fields
• Analytics early evolution of seed density
  fluctuations
• Numerics collapse and fragmentation of nonlinear
  structure
• Tools HD simulations, SPH, N-Body, Radiative
  Transfer
• 1st light from stars and quasars ended the dark
  ages (Rees) of the universe a renaissance of
  enlightenment
• Reionization epoch

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Lya Forest Reionization Redshift
overlapping bubbles
first ionisators
emanating HII regions

• lc 912 A
• absorption by photoionization
• of H and He

la 1216 A lb 1026 A
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Optical spectrum of Quasar with z 5.8
observational diagnosis Universe is fully
ionized at z 5.8! When and how was the IGM
ionized?
Fan et al. 2000
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Key ingredients for Reionization

• Need intergalactic ionizing radiation field
• a Radiative Feedback
• Sources/Ionisators escape radiation of
• first stars Quasars
• current reionization models with isotropic point
  sources (Gnedin 2000, Miralda-Escudé et al. 1999)
• Sources embedded in densest regions (halos)
• Constraint reionization simulation resolution
• Simplification point sources in large-scale IGM!
• Challenges
• clumpiness (radiation affected strongly by
  inhomogeneous effects)
• HD feedback (winds, SN)

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Ionization fronts in the IGM

• radiation of first ionisators a HII bubbles
  (Strömgren spheres)
• H ionization threshold 13.6 eV
• Stellar ionizing spectrum most photons above
  threshold
• CS high a thin HI layer suffices to absorb all
  photons!
• no He contributions!
• Model assumptions spherical ionized volume
• Recombination very high in high-density clumps
• Maximum comoving radius (neglect recombination,
• SCDM WB 0.045, WM 0.3, WL 0.7 Ng
  ionizing photons
• per baryon, Nion ionizations per baryon, M
  halo mass,
• n0H present number density of H)

Loeb et al. 2000
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Reionization of Hydrogen in the IGM
I initial pre-overlap stage
individual sources escape photons find their way
through high-density regions (high recombination
rate!) IGM is two-phase medium a highly ionized
regions a neutral regions ionization intensity
very inhomogeneous
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Reionization of Hydrogen in the IGM
II rapid overlap phase of reionization
higher exposition by ionizing photons! a
ionization intensity increases rapidly a
expansion into high-density gas a several
unobscured sources a ionization intensity more
homogeneous
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Reionization of Hydrogen in the IGM
II moment of reionization
ionization radiation does NOT reach
self-shielded, high-density clouds a end of
overlap phase
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Reionization of Hydrogen in the IGM
III post-overlap phase This continues
indefinitely, since collapsed objects retain
neutral gas even in present universe. Milestone
at zbr 1.6 a breakthrough redshift Below
zbr all ionizing sources are visible! Above zbr
absorption by Lya forest clouds a Only sources
in small redshift range are visible!
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Reionization of Hydrogen in the IGM

• Vmax 4/3prmax3

• solid source switch-on _at_ z 10

• dashed source switch-on _at_ z 15

Scalo et al. (1998)
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Evolution of filling factor

• Nion 40

• clumping factor
• C const

• dashed collapse
• fraction Fcol

• dotted obs. lower limit for zreion
• (Fan et al. 2000)

• Recombination less important
• at HZ!

Loeb et al. 2000
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Consequences

• Star-forming galaxies in CDM hierarchical models
  can explain reionization of the universe
• at z 6 15
• Further contributes for ionization by
• mini-quasars is possible
• uncertain parameters for determining zreion
• Source parameters
• formation efficiency of stars and quasars
• escape fraction of ionizing sources
• Clumping factor C depends on the density and
  clustering of the sources
• source halos form in overdense regions
• a C depends on sources and IGM density

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Gnedin 2000 - Stellar Reionization Simulations
Setup

• LCDM with Wm 0.3
• radiative transfer code
• periodic boundary conditions
• 1283 DM, 1283 baryonic particles (mb 5x105 M8)
• thin slices through a Mpc box with 4 h-1 per side
• J21 mean ionization intensity at Lyman limit
• (in units of 10-21 erg cm-2 s-1 sr-1 Hz-1)
• J21 inside HII regions depends on absorption and
  RT through IGM
• includes local optical depth effects
• does not include shadowing

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Gnedin 2000Reionization Simulations
z 11.5
redshift evolution of log from mean ionization
density
log of HI fraction
gas density
gas temperature
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Gnedin 2000 Reionization Simulations
z 9.0
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Gnedin 2000 Reionization Simulations
z 7.7
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Gnedin 2000 Reionization Simulations
z 7.0
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Gnedin 2000 Reionization Simulations
z 6.7
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Gnedin 2000 Reionization Simulations
z 6.1
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Gnedin 2000 Reionization Simulations
z 5.7
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Gnedin 2000 Reionization Simulations
z 4.9
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Gnedin 2000 - Stellar Reionization Simulations
Results

• ionized bubbles emanate from main
• concentrations of sources
• sources located in highest density regions (C
  100)
• bubbles expand in low density regions in IGM
• finally bubbles overlap
• complex topology of ionized regions
• neutral islands remain in highest density regions
• But rough approximations in RT have to be
  treated more accurately and then explored in
  detail

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Quasar Reionization
vs.
Stellar Reionization

• bright point-source
• a HII funnel (in disk)
• a photons escape through channel!
• hard quasar photons
• a penetrate deeper into neutral gas
• a thicker ionization front
• Quasar X-photons catalyze H2 molecule formation
• a stars form in tiny halos (Haiman, Abel Rees,
  1999)
• BUT hardness of ionization spectrum depends of
  
• initial mass function!

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The Loeb-Rybicki halo

• Diffuse Lya halos due to Hubble expansion
• Tool for probing distribution and velocity field
  of neutral IGM before epoch of reionization
• Disappearance of Lya halos signals zreion !

• Detection challenge
• low surface brightness!

NGST
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21cm tomography in the pre-reionization epoch

• Hyperfine structure transition spin-flip from
• triplet to singlet state traces HI regions
• Observability
• ground-state thermalizes with CMB
• perturbation of thermal equilibrium by collisions
  
• and scattered Lya photons
• map redshifted 21cm emission at HZ to reveal
  neutral pre-ionization IGM (pre-overlap stage I)
• Instruments Square Kilometer Array (SKA)

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The Evolution of the SFR
hSFR 10 (obs. indicated)
Blain et al. 1999
upper total SFR
lower NGST fract. flim 0.25 nJy
Reionization s Reheating s Suppressed SFR
Barkana Loeb 2000
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He - Reionization

• HeI a He II by 24.6 eV photons
• He II ionization threshold _at_ 54.4 eV
• a Reionization of He II later (lower z!) than HI
• a He - Reionization more observable! (H
  preview)
• nH/nHe 13 He more rare a no prob!

• Observational probe
• heating of IGM due to hard ionisators
• a H reionization TIGM 104 K
• a He reionization TIGM gt 2 x 104 K
• a hotter IGM suppresses dwarf galaxy formation
• TIGM measurements
• search for smallest line-widths
• among H Lya absorption lines
• Schaye et al. 2000
• isothermal IGM with T 2 x 104 K _at_ z 3

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He II Lya absorption in the IGM Q 0302-003 z
3.286
Heap et al. (2000)
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Q 0302-003 - Interpretation

• Lya absorption by intergalactic He II
• fits data for low-density IGM
• sharp opacity break at z 3.0 (l 1240 A)
• a sudden hardening of UV ionizing
• background below z 3
• a high opacity only requires 0.1 of
• He not fully ionized
• confirmation by indirect diagnosis Si-4/ C-4
  ratio
• (Songaila Cowie 1996, Songaila 1998)

• Overlap phase of full He reionization
• at higher z!

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NCSA simulation Norman et al. 1997

• Numerical hydrodynamics
• simulation of the Lya forest
• gas density distribution at z3
• CDM spectrum of primordial density fluctuations
• H0 50 km/s
• comoving box size of 9.6 Mpc
• Wb 0.06 ( 76 H, 24 He)
• cube side 2.4 Mpc (proper)
• Isosurfaces baryons at ten times mean
• cosmic density
• Tgas 3 x 104 K (dark blue)
• Tgas 3 x105 K (light blue)
• single random slice through cube shows baryonic
  overdensity represented by a rainbow--like color
  map (blackmin to redmax)
• HeII mass fraction wire mesh in same slice (fine
  structure)
• fine structure in minivoids rescaled mass
  fraction in
• overdense regions by gas overdensity wherever it
  exceeds unity.

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The Reionization Challenge

• How much ionizing sources are available?
• a Extrapolation from observed populations of
  galaxies and quasars to HZ (Madau et al. 1999,
• Miralda-Escudé et al. 2000)
• a Conclusion
• HZ source population is similar to the one
  observed at z 3 4 and suffices to produce
• the J21 needed!
• a But
• ? Escape fraction ?
• ? Luminosity function ?
• ? Clumping factor ?
• ? Recombination ?
• WANTED! further constraining observations
  WANTED!

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Future Instruments

• Observational efforts to dive into HZ regime
• further space-telescopes large ground-based
  telescopes (optical 30 m diameter radio SKA)
• NGST (launch 2009 planned)
• sub-nJy sensitivity in IR range (1-3.5 mm)
• probing optical-UV sources at z gt 10
• Popular CDM models predict 1st baryonic
• objects at z 10
• Future change focus from
• LSS (Large Scale Structure)
• to
• SSS (Small Scale Structure)
• Waiting for observational input data from
• NGST, MAP, Planck, CAT, CBI SKA
• Next decade high precision cosmology

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Summary
Primordial Objects at z 30
Lya Systems probe Reionization epoch z 7
Reionization studies by LR halo, 21cm, SFR
counts
Tune and Refine Simulations
Constraints by Observational Input
Cosmology in the 21. Century SSS
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References

• Loeb a astro-ph/0010467, 0011529
• Gnedin a astro-ph/0002151, 0008469, 9909383
• Fan a astro-ph/0005414
• Heap a ApJ 534, 69-891 (2000)
• Schaye a astro-ph/9912432
• Bromm a astro-ph/9910224, 0103382, 0104271
• URLs
• http//casa.colorado.edu/gnedin
• http//cfa-www.harvard.edu/Loeb
• http//www.hep.upenn.edu/max/index.html
• http//background.uchicago.edu/whu
• http//zeus.ncsa.uiuc.edu8080/LyA/minivoid.html