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Cosmic reionization and the history of the neutral intergalactic medium
MAGPOP Summer School, Kloster Seeon
Chris Carilli, NRAO, August 10, 2007
Introduction: What is Cosmic Reionization?
Current constraints on the IGM neutral fraction with cosmic epoch
Neutral Intergalactic Medium (IGM) – HI 21cm signals
Low frequency telescopes and observational challenges
References
Reionization and HI 21cm studies of the neutral IGM
“Observational constraints on cosmic reionization,” Fan, Carilli, Keating 2006, ARAA, 44, 415
“Cosmology at low frequencies: the 21cm transition and the high redshift universe,” Furlanetto, Oh, Briggs 2006, Phys. Rep., 433, 181
Early structure formation and first light
“The first sources of light and the reionization of the universe,” Barkana & Loeb 2002, Phys.Rep., 349, 125
“The reionization of the universe by the first stars and quasars,” Loeb & Barkana 2002, ARAA, 39, 19
“Observations of the high redshift universe,” Ellis 2007, Saas-Fe advanced course 36
Ionized
Neutral
Reionized
History of Baryons in the Universe
Chris Carilli (NRAO)
Berlin June 29, 2005
WMAP – structure from the big bang
Hubble Space Telescope Realm of the Galaxies
Dark Ages
Twilight Zone
Epoch of Reionization
• Last phase of cosmic evolution to be tested • Bench-mark in cosmic structure formation indicating the first luminous structures
Dark Ages
Twilight Zone
Epoch of Reionization
• Epoch?• Process?• Sources?
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
Gnedin 03
Reionization: the movie
8Mpc comoving
Barkana and Loeb 2001
Constraint I: Gunn-Peterson Effect
z
Gunn-Peterson Effect toward z~6 SDSS QSOs
Fan et al 2006
Gunn-Peterson limits to f(HI)
• to f(HI) conversion requires ‘clumping factor’
• >>1 for f(HI)>0.001 => low f() diagnostic
• GP => Reionization occurs in ‘twilight zone’, opaque for obs <0.9 m
GP = 2.6e4 f(HI) (1+z)^3/2
End of reionization?
f(HI) <1e-4 at z= 5.7
f(HI) >1e-3 at z= 6.3
Contraint II: The CMB
Temperature fluctuations due to density inhomogeneities at the surface of last scattering (z ~ 1000)
Angular power spectrum ~ variance on given angular scale ~ square of visibility function
Sound horizon at recombination ~ 1deg
Sachs-Wolfe
No reionization
ReionizationThomson scatting during reionization (z~10)
Acoustics peaks are ‘fuzzed-out’ during reionization.
Problem: degenerate with intrinsic amplitude of the anisotropies.
Reionization and the CMB
TT
TE
EE
CMB large scale polarization -- Thomson scattering during reionization
Scattering CMB local quadrapole => polarized
Large scale: horizon scale at reionization ~ 10’s deg
Signal is weak:
TE = 10% TT (few uK)
EE = 1% TT
EE (l ~ 5)~ 0.3+/- 0.1 uK
Page + 06; Spergel 06
e ~ l / mfp ~ l ne e (1+z)^2 = 0.09+/-0.03
TT
TE
EE
Constraint II: CMB large scale polarization -- Thomson scattering during reionization
Rules-out high ionization fraction at z> 15
Allows for finite (~0.2) ionization to high z
Most action occurs at z ~ 8 to 14, with f(HI) < 0.5
Page + 06; Spergel 06
e = integral measure to recombination=> allows many IGM histories
• Still a 3 result (now in EE vs. TE before)
Combined CMB + GP constraints on reionization
• tuniv = 0.87Gyr• Lbol = 1e14 Lo
• Black hole: ~3 x 109 Mo (Willot etal.)• Gunn Peterson trough (Fan etal.)
Pushing into reionization: QSO 1148+52 at z=6.4
1148+52 z=6.42: Gas detection
Off channelsRms=60uJy
46.6149 GHzCO 3-2
• M(H2) ~ 2e10 Mo
• zhost = 6.419 +/- 0.001
(note: zly = 6.37 +/- 0.04)
VLA
IRAM
VLA
Constrain III: Cosmic Stromgren Sphere
• Accurate zhost from CO: z=6.419+/0.001
• Proximity effect: photons leaking from 6.32<z<6.419
z=6.32
•‘time bounded’ Stromgren sphere: R = 4.7 Mpc• tqso = 1e5 R^3 f(HI)~ 1e7yrs or • f(HI) ~ 1 (tqso/1e7 yr)
White et al. 2003
Loeb & Rybicki 2000
CSS: Constraints on neutral fraction at z~6 Nine z~6 QSOs with CO or MgII redshifts: <R> = 4.4 Mpc (Wyithe et al. 05; Fan et al. 06; Kurk et al. 07)
GP => f(HI) > 0.001
If f(HI) ~ 0.001, then <tqso> ~ 1e4 yrs – implausibly short given QSO fiducial lifetimes (~1e7 years)?
Probability arguments + size evolution suggest: f(HI) > 0.05
Wyithe et al. 2005
=tqso/4e7 yrs
90% probability x(HI) > curve
P(>xHI)
Fan et al 2005
Difficulties for Cosmic Stromgren Spheres
(Lidz + 07, Maselli + 07)
Requires sensitive spectra in difficult near-IR band
Sensitive to R: f(HI) R^-3
Clumpy IGM => ragged edges
Pre-QSO reionization due to star forming galaxies, early AGN activity
ESO
OI
Not ‘event’ but complex process, large variance: zreion ~ 14 to 6
Good evidence for qualitative change in nature of IGM at z~6
ESO
OI
Saturates, HI distribution function, pre-ionization?
Abundance?
3, integral measure?
Local ionization?
Geometry, pre-reionization?
Current probes are all fundamentally limited in diagnostic power
Need more direct probe of process of reionization = HI 21cm line
Local ioniz.?
Low frequency radio astronomy: Most direct probe of the neutral IGM during, and prior to, cosmic reionization, using the redshifted HI 21cm line: z>6 => 100 – 200 MHz
Square Kilometer Array
1e13 Mo
1e9 Mo
HI mass limits => large scale structure
Reionization
HI 21cm radiative transfer: large scale structure of the IGM
LSS: Neutral fraction / Cosmic density / Temperature: Spin, CMB
Dark Ages HI 21cm signal
•z > 200: T = TK = Ts due to collisions + Thomson scattering => No signal
•z ~ 30 to 200: TK decouples from T, but collisions keep Ts ~ TK => absorption signal
•z ~ 20 to 30: Density drops Ts~ T => No signal
Barkana & Loeb: “Richest of all cosmological data sets”
• Three dimensional in linear regime
• Probe to k ~ 10^3 /Mpc vs. CMB limit set by photon diffusion ~ 0.2/Mpc
•Alcock-Pascinsky effect
•Kaiser effect + peculiar velocites
TK = 0.026(1+z)^2
T = 2.73(1+z)
Furlanetto et al. 2006
Enlightenment and Cosmic Reionization -- first luminous sources
•z ~ 15 to 20: TS couples to TK via Lya scattering, but TK < T => absorption
•z ~ 6 to 15: IGM is heated (Xrays, Lya, shocks), partially ionized => emission
•z < 6: IGM is fully ionized
TK
T
Signal I: Global (‘all sky’) reionization signature
Signal ~ 20mK < 1e-4 sky
Possible higher z absorption signal via Lya coupling of Ts -- TK due to first luminous objects
Feedback in Galaxy formation
No Feedback
Furlanetto, Oh, Briggs 06
Signal II: HI 21cm Tomography of IGM Zaldarriaga + 2003
z=12 9 7.6
TB(2’) = 10’s mK
SKA rms(100hr) = 4mK
LOFAR rms (1000hr) = 80mK
Signal III: 3D Power spectrum analysis
SKA
LOFAR
McQuinn + 06
only
+ f(HI)
• N(HI) = 1e13 – 1e15 cm^-2, f(HI/HII) = 1e-5 -- 1e-6 => before reionization N(HI) =1e18 – 1e21 cm^-2
• Lya ~ 1e7 21cm => neutral IGM opaque to Lya, but translucent to 21cm
Signal IV: Cosmic Web after reionization
Ly alpha forest at z=3.6 ( < 10)
Womble 96
z=12 z=819mJy
130MHz
• radio G-P (=1%)
• 21 Forest (10%)
• mini-halos (10%)
• primordial disks (100%)
Signal IV: Cosmic web before reionization: HI 21Forest
• Perhaps easiest to detect (use long baselines)
• ONLY way to study small scale structure during reionization
159MHz
Radio sources beyond the EOR
sifting problem (1/1400 per 20 sq.deg.)
2240 at z > 6
1.4e5 at z > 6
S120 > 6mJy
Signal V: Cosmic Stromgren spheres around z > 6 QSOs
0.5 mJy
LOFAR ‘observation’:
20xf(HI)mK, 15’,1000km/s
=> 0.5 x f(HI) mJy
Pathfinders: Set first hard limits on f(HI) at end of cosmic reionization
Easily rule-out cold IGM (T_s < T_cmb): signal = 360 mK
Wyithe et al. 2006
5Mpc
Signal VI: Dark Ages: Baryon Oscillations
Very low frequency (<75MHz) = Long Wavelength Array
Very difficult to detect
Signal: 10 arcmin, 10mk => S30MHz = 0.02 mJy
SKA sens in 1000hrs:
= 20000K at 50MHz =>
rms = 0.2 mJy
Need > 10 SKAs
Need DNR > 1e6
z=50
z=150
Barkana & Loeb 2005
Challenge I: Low frequency foreground – hot, confused sky
Eberg 408 MHz Image (Haslam + 1982)
• Coldest regions: T ~ 100z)^-2.6 K
• 90% = Galactic foreground
• 10% = Egal. radio sources ~ 1 source/deg^2 with S140 > 1 Jy
Solution: spectral decomposition (eg. Morales, Gnedin…)
Foreground = non-thermal = featureless over ~ 100’s MHz
Signal = fine scale structure on scales ~ few MHz
10’ FoV; SKA 1000hrs
Signal/Sky ~ 2e-5
Cygnus A
500MHz 5000MHz
Simply remove low order polynomial or other smooth function?
Cross correlation in frequency, or 3D power spectral analysis: different symmetries in frequency space for signal and foregrounds.
Freq
Signal Foreground
Morales 2003
Cygnus A at WSRT 141 MHz 12deg field (de Bruyn)
Frequency differencing ‘errors’ are ‘well-behaved’ ‘CONTINUUM’ (B=0.5 MHz) ‘LINE’ CHANNEL (10 kHz) - CONT
(Original) peak: 11000 Jy noise 70 mJy
dynamic range ~ 150,000 : 1
Galactic foreground polarization‘interaction’ with polarized beams
frequency dependent residuals!
Solution: good calibration of polarization response
NGP 350 MHz 6ox6o ~ 5 K pol IF Faraday-thin 40 K at 150 MHz
WENSS: Schnitzeler et al A&A Jan07
30o x 30o
‘Isoplanatic patch’ = few deg = few km
Phase variation proportional to wavelength^2
74MHz Lane 03
Challenge II: Ionospheric phase errors – varying e- content
TID
Solution:
Wide field ‘rubber screen’ phase self-calibration = ‘peeling’
Requires build-up of accurate sky source model
Virgo A 6 hrs VLA 74 MHz Lane + 02
QuickTime™ and aCinepak decompressor
are needed to see this picture.
15’
Ionospheric phase errors: The Movie
Challenge III: Interference
100 MHz z=13
200 MHz z=6
Solutions -- RFI Mitigation (Ellingson06)
Digital filtering: multi-bit sampling for high dynamic range (>50dB)
Beam nulling/Real-time ‘reference beam’
LOCATION!
Beam nulling -- ASTRON/Dwingeloo (van Ardenne)
Factor 300 reduction in power
VLA-VHF: 180 – 200 MHz Prime focus CSS search Greenhill, Blundell (SAO); Carilli, Perley (NRAO)
Leverage: existing telescopes, IF, correlator, operations
$110K D+D/construction (CfA)
First light: Feb 16, 05
Four element interferometry: May 05
First limits: Winter 06/07
Project abandoned: Digital TV
KNMD Ch 9
150W at 100km
RFI mitigation: location, location location…
100 people km^-2
1 km^-2
0.01 km^-2
(Briggs 2005)
Multiple experiments under-way: ‘pathfinders’
MWA (MIT/CfA/ANU) LOFAR (NL)
21CMA (China) SKA
QuickTime™ and aCinepak decompressor
are needed to see this picture.
EDGES (Bowman & Rogers MIT)
All sky reionization HI experiment. Single broadband dipole experiment with (very) carefully controlled systematics + polynomial baseline subtraction (7th order)
Treion < 450mK at z = 6.5 to 10 (DNR ~ 2700)
(expect ~ 20mK)
Sky > 150 K rms = 75 mK
VaTech Dipole Ellingson
GMRT 230 MHz – HI 21cm abs toward highest z (~5.2) radio AGN
0924-220 z=5.2
S230MHz = 0.5 Jy
1”
8GHz Van Breugel et al.
GMRT at 230 MHz = z21cm
RFI = 20 kiloJy !
CO Klamer +
M(H2) ~ 3e10 Mo
GMRT 230 MHz – HI 21cm abs toward highest z radio AGN (z~5.2)
rms(20km/s) = 5 mJy
229Mhz 0.5 Jy232MHz 30mJy
rms(40km/s) = 3mJy
N(HI) ~ 2e20TS cm^-2 ?
Limits:
Few mJy/channel
Few percent in optical depth
Focus: Reionization (power spec,CSS,abs)
PAPER: Staged Engineering Approach
• Broad band sleeve dipole => 2x2 tile
• 8 dipole test array in GB (06/07) => 32 station array in WA (12/07)
• FPGA-based ‘pocket correlator’ from Berkeley wireless lab => custom design.
BEE2: 5 FPGAs, 500 Gops/s
• S/W Imaging, calibration, PS analysis: Miriad/AIPS => Python + CASA, including ionospheric ‘peeling’ calibration + MFS
• ‘Peel the problem onion’
100MHz 200MHz
Cas A 1e3Jy CygA 1e4Jy
W44 1e2Jy HercA 1e2Jy
PAPERGB -- 8 Ant, 1hr, 12/06
RMS ~ 15Jy; DNR ~ 1e3
5deg
Destination: Moon!
RAE2 1973
No interference (ITU protected zone)
No ionosphere (?)
Easy to deploy and maintain (high tolerance electronics + no moving parts)
10MHz
Needed for probing ‘Dark ages’:
z>30 => freq < 50 MHz
Radio astronomy – Probing Cosmic Reionization
•‘Twilight zone’: study of first light limited to near-IR to radio
• First constraints: GP, CMBpol => reionization is complex and extended:
z_reion = 6 to 11
• HI 21cm: most direct probe of reionization
•Low freq pathfinders:
All-sky, PS, CSS
• SKA: imaging of IGM
END
Relative evolution of Ly-break and Ly galaxy populations: Obscuration by the neutral IGM (Ota + 2007)
Local ionization (CSS)?
Low S/N
LAE observed z=5.7LAE predicted z=7
based on UV continuum
LAE obs z=7
At z=7 => f(HI)=0.48+/-0.16
Dark Matter
Press-Schechter Formalism
z M2 Tvir
Msun K
0 1e14 3e7
5 3e10 3e5
10 6e7 8e3
•M’Jeans’ = 1e4 Msun (z=20)
•Minihalos: H2 cooling: Tvir = 300 to 1e4 K => M = 1e5 to 1e8 Msun
issues:
primordial H_2 formation?
Near UV dissociates H_2?
Soft Xray catalyzes H_2 formation?
Preferentially form 100 M_sun stars (popIII)?
•Protogalaxies: H line cooling => T_vir > 1e4 K
Baryons: astrophysics
Early structure formation: rules-of-thumb (Barkana & Loeb 2002)
Some basics
Structure formation: the Dark Matter perspective = Press-Schechter Formalism
z M_2 T_vir
M_sun K
0 1e14 3e7
5 3e10 3e5
10 6e7 8e3
• Minihalos z>15: M=1e5 to 1e8Mo
=> Tvir = 300 to 1e4 K => H2 cooling
Primordial H2 formation?
Near UV dissociates H2?
Soft Xray catalyzes H2 formation?
Preferentially form 100 Mo stars?
• Protogalaxies z<15: 1e8Mo => Tvir > 1e4 K => HI line cooling
[Cosmological Jeans mass < 1e4 Mo at z>20]
Some basics
Structure formation: the Baryons
Cosmic Stromgren Surfaces (Hui & Haiman)
• Larger CSS in Ly vs. Ly = Damping wing of Ly?
• Large N(HI) (> 1e20cm^-2) => f(HI) > 0.1
zhost
GMRT Digital Filter in Lag-space (Pen et al. 2007)
150 MHz
Cen 2002
Some basics: What’s time…?
• Stellar fusion produces 7e6eV/H atom.
• Reionization requires 13.6eV/H atom
=>Need to process only 1e-5 of baryons through stars to reionize the universe
At z>6
tuniv < 1 Gyr
At z > 8 trecombination < tuniv
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