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

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COBE data reveal fluctuations in CMB in mK domain. Large scale CMB ... results: flat universe with LCDM cosmology. L 0 WL ~ 0.62. WB ~ 0.05 WCDM ~ 0.33 ... – PowerPoint PPT presentation

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


1
The first sources of light in the Early Universe
and the highest plausible redshift of luminous
Quasars
  • Andreas Müller
  • Landessternwarte Heidelberg
  • Oberseminar 2001
  • Entstehung von Quasaren

2
Overview
The Cosmological Setup
Primordial Objects
Cosmological Ingredients
The Lya Forest
Reionization
zreion measurements
Gnedin Simulations
Reionization Tools
Future Instruments Challenges
3
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

4
Milestones in the history of the Universe
5
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
6
Gas-Clump Morphology at z 28
30 pc
Bromm et al. 2001
7
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
8
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

9
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

10
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
11
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
12
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)

13
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
14
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
15
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
16
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
17
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!
18
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)
19
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
20
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

21
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

22
Gnedin 2000 Reionization Simulations
z 11.5
redshift evolution of log from mean ionization
density
log of HI fraction
gas density
gas temperature
23
Gnedin 2000 Reionization Simulations
z 9.0
24
Gnedin 2000 Reionization Simulations
z 7.7
25
Gnedin 2000 Reionization Simulations
z 7.0
26
Gnedin 2000 Reionization Simulations
z 6.7
27
Gnedin 2000 Reionization Simulations
z 6.1
28
Gnedin 2000 Reionization Simulations
z 5.7
29
Gnedin 2000 Reionization Simulations
z 4.9
30
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

31
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!

32
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
33
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)

34
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
35
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

36
He II Lya absorption in the IGM Q 0302-003 z
3.286
Heap et al. (2000)
37
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!

38
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.

39
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40
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!

41
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

42
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
43
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
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