The first Sources of Light

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21cm Cosmology
Avi Loeb Harvard University
Collaborators Rennan Barkana, Stuart Wyithe,
Matias Zaldarriaga
Moscow 2004
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Los Alamos, May 19, 2005
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Mapping Cosmic Hydrogen In the Infant Universe
Avi Loeb Harvard University
Collaborators Rennan Barkana, Stuart Wyithe,
Matias Zaldarriaga
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On small scales the universe is clumpy
Early times
Density perturbation
Mean Density
Intermediate times
Late times
Bound Object
Void
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Current Composition of the Universe
Silk damping of small-scale fluctuatons in the
baryon-photon fluid prior to cosmic recombination
implies that galaxies could not have formed in
our Universe without dark matter!
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The First Dark Matter Objects in the Universe
Smallest dark matter clumps 0.1 Jupiter mass
Diemand, Moore Stadel astro-ph/0501589
Loeb Zaldarriaga, astro-ph/0504112
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Emergence of the First Star Clusters
molecular hydrogen in Jeans mass objects
Yoshida et al. 2003
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Ionization History of Hydrogen
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REDSHIFT
1000
Big Bang
Now
TIME
Million years
Billion years
Neutral Hydrogen (HI)
Ionized
Ionized
by the first stars and quasars
Tgt3000 K
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Hydrogen
e-
p
Ground level
excitation rate (atomic collisions)(radiative
coupling to CMB)
Couples to
Couple to
spin
p
e-
p
e-
Spin Temperature
Predicted by Van de Hulst in 1944 Observed by
Ewen Purcell in 1951 at Harvard
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21 cm Absorption by Hydrogen Prior to Structure
Formation
Fluctuations in 21cm brightness are sourced by
fluctuations in gas density
Loeb Zaldarriaga, Phys. Rev. Lett., 2004 Scott
Rees, MNRAS, 1990
Observed wavelength21cm (1z) ? 3D tomography
(slicing the universe in redshift )
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Largest Data Set on the Sky
Number of independent patches
while Silk damping limits the primary CMB
anisotropies to only
Noise due to foreground sky brightness
Loeb Zaldarriaga, Phys. Rev. Lett., 2004
astro-ph/0312134
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Line-of-Sight Anisotropy of 21cm Flux Fluctuations
Peculiar velocity changes
? Power spectrum is not isotropic (Kaiser
effect)
observer
terms allow separation of powers
Barkana Loeb, astro-ph/0409572 see also
Bharadwaj Ali, astro-ph/0401206
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Acoustic Oscillations
sound wave
Inflation t0
Gas is freed to fall into dark matter potential
fluctuations at z1000

• Correlation across the radiation sound horizon,
  left over from coupling of gas to CMB at zgt1000.
• Standard ruler- sensitive probe to cosmological
  parameters.

Barkana Loeb 2005
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Enhancement of 21cm Fluctuations During the
Period of Initial Lya Coupling of the spin T to
the kinetic T
Wouthuysen-Field Effect
n2
Lya
saturated
21cm
n1
Fluctuations in the distribution of galaxies
induce fluctuations in Lya intensity ?21cm
Rapid evolution in retarded time
horizon
Barkana Loeb, astro-ph/0410129
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Enhancement of 21cm Fluctuations During the Epoch
of Initial Lya Coupling
Sourced by fluctuations in Lya intensity from
galaxies
Power spectrum of 21cm brightness fluctuations
Biased fluctuations in the density of galaxies
Poisson fluctuations in the number of galaxies
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Thermal History
Temperature
Radiative coupling to CMB
atomic collisions
X-ray heating
redshift
z200
z30
Wouthuysen-Field Effect
Sources of 21cm fluctuations

Density inhomogeneties
(Loeb Zaldarriaga 04) and peculiar velocities
(Barkana Loeb 04)

Ionized bubbles (Madau,Meiksin Rees
1997Furlanetto et al. 2004 Gnedin Shaver
2003) Emision from mini-halos (Iliev, Shapiro, et
al. 2002)
Fluctuations in
Lya flux, and gas temperature (Barkana Loeb
2004)
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History of 21cm Brightness Fluctuations

HI appears in absorption against the CMB
X-ray heating to
Lya coupling of spin temperature to
kinetic temperature
HI appears in emission against the CMB
Reionization HI gradually disappears
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21cm Tomography of Ionized Bubbles During
Reionization is like Slicing Swiss Cheese
H II
H I
Observed wavelength? distance
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Is the 21cm signal polarized?
Intrinsic Polarization

• Zeeman effect requires unrealistic intergalactic
  magnetic fields (100 micro-gauss on Mpc scales)
  at z10 (Cooray Furlanetto 2005).
• Quadrupole in local Lya illumination eliminated
  by the very large Lya optical depth
  .

Secondary Polarization

• Thomson scattering free electrons in the
  reionized universe scatter the 21cm photons.

unpolarized
polarized
e-
e-
e-
HI
e-
e-
21cm
21cm
21
e-
first line of sight
e-
second line of sight
end of reionization
observer
e-
e-
e-
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21cm Polarization from Thomson Scattering
Power-spectrum of brightness/E-type polarization
cross-correlation (TE)
21cm fluctuations from Poisson statistics of
ionized bubbles at the end of a rapid
reionization
Babich Loeb (2005)
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Experiments
MWA (Mileura Wide-Field Array) MIT/ATNF/CfA
LOFAR (Low-frequency Array) Netherlands
PAST (Primeval Structure Telescope) China/CITA
Enhanced VLA CfA/NRAO
SKA (Square Kilometer Array)
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Milleura Wide-Field Array mapping cosmic
hydrogen through its 21cm emission

• 4mx4m tiles of 16 dipole antennae, 80-300MHz
• 500 antenna tiles with total collecting area 8000
  sq.m. at 150MHz across a 1.5km area few arcmin
  resolution

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Mileura Wide-Field Array
A very radio quiet site
Antenna design
MIT, ATNF, U. Melbourne, CfA
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Characteristics of MWA demonstrator

• 500 16-element antennas in a compact 1.5km array
• Wide 80-300 MHz frequency range
• Digital receiver and filter chain, 32 MHz at 16
  kHz resolution
• Full cross-correlation of all 500 antennas, 20-30
  degrees field of view

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Enhanced VLA (Greenhill et al.) Placement of
Proposed VHF Feeds
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The Primeval Structure Telescope (PAST) in China
Peterson, Pen, Wu astro-ph/0502029
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Primary challenge foregrounds

• Terrestrial radio broadcasting
• Galactic synchrotron emission
• Extragalactic radio sources
  (Di-Matteo et al. 2004)

Although the sky brightness (gt10K) is much larger
than the 21cm signal (lt10mK), the foregrounds
have a smooth frequency dependence while the
signal fluctuates rapidly across small shifts in
frequency (redshift). Preliminary estimates
indicate that the 21cm signal is detectable with
the forthcoming generation of low-frequency
arrays (Zaldarriaga et al. astro-ph/0311514
Morales Hewitt astro-ph/0312437)
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James Webb Space Telescope (successor to Hubble
Space Telescope) Searching for the First Light
Mirror diameter 6.5 meter Material beryllium 18
segments Wavelength coverage 0.6-28 micron L2
orbit 1 billion
Launch date 2013
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Giant Magellan Telescope

• Seven mirrors, each 8.4m in diameter
• Equivalent resolving power to a 24.5m primary

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When was the Universe Reionized?
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Empirical Hints
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Cosmic Microwave Background (WMAP)
The polarization data indicates that the first
stars must have formed 400 million years after
the big bang, when the universe was only a few
percent of its current age!
Page et al. 2006
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Have we observed the Gunn-Peterson Trough?
Fan et al. 2005
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Cosmic Hydrogen was significantly Neutral at
z6.3
Size of HII region depends on neutral fraction of
IGM prior to quasar activity and quasar age
Ionization(Stromgren) sphere of quasar
line of sight
R(t)
Wyithe Loeb, Nature, 2004 astro-ph/0401188
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The Earliest Quasar Detected z6.4
Fan et al. 2002
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Likelihood for Neutral Fraction at z6.3
SDSS J11485251
Wyithe Loeb, astro-ph/0401188 Wyithe, Loeb,
Carilli, astro-ph/0411625
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Imaging the Neutral Fraction in 21cm
21 cm
Warm HI X-ray heated by quasar
quasar
HII
reionization
Warm HI
Brightness
CMB
Cold HI
wavelength
21 cm absorption of CMB if IGM is cold or
21 cm emission due to heating by X-ray
background or quasar X-rays (but no Lyman-alpha
heating by the quasar)
Wyithe and Loeb 2004 astro-ph/0401554 Tozzi,
Madau, Meiksin, Rees 2000
100x relic shells per known quasar
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Emission from an X-ray Heated IGM
Wyithe Loeb 2004 astro-ph/0401554
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Simulated MWA Images of a Quasar HII Region
(Spherical or Conical)
Wyithe, Loeb Barnes (2005)
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Finding Massive Galaxies from their Ionized
Regions
Infrared imaging
Galaxy/Quasar
HI hole
21cm mapping
Wyithe, Loeb Barnes (2005)
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The Characteristic Size of Ionized Bubbles at the
End of Reionization
Fig. 1
SBO Surface of Bubble Overlap
SLT Surface of Lya Transmission
Wyithe Loeb, Nature, 2004
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SDSS quasars at zgt6.1
SLT
HI
photon

• Causality crossing time of bubble by a 21cm
  photon
• .
• Cosmic variance cosmic scatter in the formation
  time of ionized bubbles due to large-scale
  inhomogeneities

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Summary

• Redshifted 21cm from 30ltzlt200 provides the
  largest data set on the initial conditions of the
  universe
• Peculiar velocities provide additional power and
  a test for the cosmological origin of the 21cm
  signal
• The size of the ionized bubbles at the end of
  reionization was 10 Mpc
• Foreground removal is very challenging

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How Did the First Massive Black Holes Form?
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Formation of Massive Black Holes in the First
Galaxies
Add Bromm
Low-spin systems Eisenstein Loeb
1995 Numerical simulations Bromm Loeb 2002
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Supermassive Stars
For a spherical (non-rotating) star general-relat
ivistic instability at
Angular momentum mass shedding along
equator
Collapse to a black hole is inevitable for
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Why Are Quasars Short Lived?

Because they are suicidal!
Principle of Self Regulation supermassive black
holes grow until they release sufficient energy
to unbind the gas that feeds them from their host
galaxy
?Implies a correlation between black hole mass
and the depth of the gravitational potential well
of its host galaxy
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Self-regulation of Supermassive Black Hole Growth
quasar
galactic disk
Silk Rees 1998 Wyithe Loeb 2003
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Correlation between black hole mass and velocity
dispersion of host stellar system
Tremaine et al. 2002
Ferrarese 2002
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Quasar Luminosity Function
Simple physical model Each galaxy merger leads
to a bright quasar phase during which the black
hole grows to a mass and
shines at the Eddington limit. The duration of
this bright phase is dictated by the dynamical
time of the host galactic disk (7 of the total
energy release can unbind the disk on its
dynamical time). Merger rate based on the
extended Press-Schechter model in a LCDM
cosmology.
duty cycle 10 Myr
Wyithe Loeb astro-ph/0304156
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Clustering Statistics of Quasars
Lines correlation function of model with
(SIS)
Data points 2dF Quasar Survey (Boyle et al. 2000)
Wyithe Loeb 2004 astro-ph/0403714
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Data on Quasar Clustering/LF Implies

• Local relation between galactic halo/black-hole
  redshift evolution of quasar correlation length
  are consistent with
• and not
• If mergers trigger quasar activity, then quasar
  lifetime scales with dynamical time of host
  galaxy
• rather than the
  redshift-independent Salpeter-Eddington time for
  its growth
  

Wyithe Loeb 2004 astro-ph/0403714
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Hydrodynamic Simulations of Quasar Feedback
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Hydrodynamic Simulations of Quasar Feedback
(Springel, Di Matteo, Hernquist 2004)
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(Springel, Di Matteo, Hernquist 2004)
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(i) Should we trust numerical simulations or
analytic models?
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Cooling Rate of Primordial Gas
n0.045 cm-3
Atomic cooling
H_2 cooling
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Virial Temperature of Halos
Atomic cooling
H_2 cooling
3-sigma
1-sigma
2-sigma
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Unusually Large Fluctuations in the Statistics of
Galaxy Formation at High Redshifts
Bias in numerical simulations
L
Barkana Loeb, ApJ, 2003 astro-ph/0310338
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Does the Detection of Lya Emission from
High-Redshift Galaxies Imply that the IGM Had
Already Been Reionized?
stars / unseen quasars
galaxy / cluster of faint galaxies
contributions of unseen sources
Wyithe Loeb, astro-ph/0407162
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A Galaxy at a Redshift 10?
Pello et al., 2004 astro-ph/0403025
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But if it were, was the IGM Reionized at z10?
galaxy
line-of-sight
H

• Neutral fraction lt0.4 in the large-scale region
  around that galaxy, or galaxy harbors metal-free
  stars that create a sufficiently large HII region
  in IGM.
• Lya damping wing from outside Stromgren sphere
  allows Lya line transmission.
• Resonant absorption inside Stromgren sphere may
  be suppressed by peculiar velocity relative to
  IGM.

Loeb, Barkana, Hernquist 2004
astro-ph/0403193
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Theoretical Insights
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(ii) Was Reionization Caused by Metal-Free or
Metal-Rich Stars?
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Massive Accretion by Pop-III Proto-Stars
23.5pc
0.5pc
Resolving accretion flow down to 0.03 pc
Bromm Loeb, New Astronomy, 2004
astro-ph/0312456
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Number of ionizing photons (gt13.6eV) per baryon
incorporated into stars
Massive, metal free stars
Metal free
Salpeter mass function
Bromm, Kudritzki, Loeb 2001, ApJ, 552, 464
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SPH Simulation of a Hypernova Explosion
1kpc
Bromm, Yoshida, Hernquist 2003
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Minimum Carbon and Oxygen Abundance Required for
the Formation of Low-Mass Stars
Lines Cooling rate by C II or O I allows
fragmentation in metal-poor gas clumps
Filled points halo dwarf stars
Open squares giant stars
Bromm Loeb, Nature, 2003 astro-ph/0310622
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Reionization Histories of H, He
Free Parameters (i) transition redshift,
z_tran, above which the stellar IMF is dominated
by massive, zero-metallicity stars (ii) the
product of the star formation efficiency and the
escape fraction of ionizing photons in galaxies,
.
H He He
Quasar model fits luminosity function data up to
z6
Wyithe Loeb 2002
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Visibility Function due to Electron Scattering
Scattering probability per conformal time g
failed overlap
successful overlap
Wyithe Loeb 2002
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Is double-reionization physically plausible?
Pop III/Pop II transition due to enrichment by
outflows
Change in minimum galaxy mass due to
photoionization heating/ dissociation
Outflows are much slower than ionization fronts
Extreme parameters are required for
double-reionization
Probably notbut extended
Furlanetto Loeb, astro-ph/0409656
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Other Feedback from First Stars
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Binding Energy of Dark Matter Halos
Supernova
3-sigma
1-sigma
2-sigma
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Self-Regulated Star Formation
Primordial Gas Cloud
(Dekel Silk 1986)
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Gamma-Ray Bursts Probing one Star at a Time
Collapse of a Massive Star (accompanied by a
supernova )
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Detectability of Afterglow Emission Near the Lya
WavelengthPhotometric redshift identification
based on the Lya trough
z5
z7
z9
z11
z15
JWST sensitivity
Barkana Loeb 2003 astro-ph/0305470
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Weak contamination by Lya emission line
Infall onto Massive Host Galaxy
Quasars get fainter with increasing redshift
because galaxies are less massive and the
luminosity distance increases at higher redshifts!
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Advantages of GRB Afterglows Relative to Quasars
(see details in astro-ph/0307231)

• Luminous stellar sources high redshifts
• outshine galaxies and quasars, as they become
  less luminous at increasingly higher redshifts
• -ray trigger allows all-sky monitoring
• Featureless broad-band spectra extending into the
  rest-frame UV
• absorption features can be used to probe the
  ionization and metallicity states of the IGM
• Observed flux at a fixed observed age does not
  fade significantly with increasing GRB redshift
  (cosmological time stretching counteracts
  increase in luminosity distance)
• Weak Feedback on Surrounding IGM
• - Short-lived event negligible ionizing
  effect of a GRB on the IGM
• -Low mass host galaxies weak IGM infall
  Lya line emission

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Fraction of GRBs Above a Given Redshift
All GRBs
Swift
BATSE
Results are sensitive to the uncertain GRB
luminosity function.
Bromm Loeb 2002
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Probes of Neutral Hydrogen 21 cm Absorption
source
observer
HI
Contributions Gaseous mini-halos and
disks (Furlanetto Loeb 2002) Sheets and
filaments in the intergalactic medium (Carilli,
Gnedin, Owen 2002)
Z8
Detection with the planned Low Frequency Array
(LOFAR) and Square Kilometre Array (SKA) is
feasible for sources brighter than 10 mJy at z10.
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New Insights About Reionization

• Intergalactic hydrogen was significantly neutral
  at z6.3.
• Low-mass stars started to form at a carbon/oxygen
  abundance of 0.1 solar.
• Current numerical simulations of reionization are
  significantly biased due to their periodic
  boundary conditions.
• GRBs are ideal probes of reionization.
• 21cm absorption map of CMB from z30-200 provides
  the largest data set on the sky.

Collaborators Rennan Barkana, Volker Bromm,
Staurt Wyithe All insights are described in
papers posted on astro-ph over the past 12 months.
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Neutral IGM Fraction from HII Regions Around 7
Quasars at zgt6
Wyithe Loeb, astro-ph/0411625
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Predicted Redshift Distribution of GRBs
GRB fraction with redshift gtz on the sky
Bromm Loeb 2002
Fraction of stellar mass formed by redshift z
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Planned for launch in 2004
Challenge select photometrically all
high-redshift GRBs (using the Lya break) and
follow-up on them spectroscopically
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Quasar Luminosity Function
Wyithe Loeb 2004 astro-ph/0403
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System Diagram
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EOR Data Path
EOR Data Processing
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Power Spectrum
MWA demonstrator, 100 hours, z 10
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First Year Data from WMAP
Polarization/temperature correlation implies an
electron-scattering optical depth after
cosmological recombination at z1088 of
Implying that the universe was reionized at
Only 200 million years after the big bang
Kogut et al. 2003