1. Cosmic reionization and the history of the neutral intergalactic medium
Santa Fe
Chris Carilli July 17, 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

2. 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

3. History of Baryons in the Universe
Ionized
Neutral
Reionized

4. WMAP – structure from the big bang
Chris Carilli (NRAO)
Berlin June 29, 2005
WMAP – structure from the big bang

5. Hubble Space Telescope Realm of the Galaxies

6. Dark Ages
Epoch of Reionization
Twilight Zone
Last phase of cosmic evolution to be tested
Bench-mark in cosmic
structure formation
indicating the first
luminous structures

7. Dark Ages
Epoch of Reionization
Twilight Zone
Epoch?
Process?
Sources?

8. Reionization: the movie
Gnedin 03
8Mpc comoving

9. Some basics: What’s time…?
At z > 8 trecombination < tuniv
At z>6
tuniv < 1 Gyr
Cen 2002
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

10. Constraint I: Gunn-Peterson Effectz
Barkana and Loeb 2001

11. Gunn-Peterson Effect toward z~6 SDSS QSOs
Fan et al 2006

12. Gunn-Peterson Optical depth
z < <3
z > >7

13. Gunn-Peterson limits to f(HI)
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
 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

14. Contraint II: The CMB
Temperature fluctuations due to density inhomogeneities at the surface of last scattering (z ~ 1000)
Sound horizon at recombination ~ 1deg
Angular power spectrum ~ variance on given angular scale ~ square of visibility function
Sachs-Wolfe

15. Reionization and the CMB
No reionization
Reionization
Thomson scatting during reionization (z~10)
Acoustics peaks are ‘fuzzed-out’ during reionization.
Problem: degenerate with intrinsic amplitude of the anisotropies.

16. e ~ l / mfp ~ l ne e (1+z)^2 = 0.09+/-0.03
CMB large scale polarization -- Thomson scattering during reionization
Page + 06; Spergel 06
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 TT TE EE
e ~ l / mfp ~ l ne e (1+z)^2 = /-0.03

17. Rules-out high ionization fraction at z> 15
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 TT TE EE
Page + 06; Spergel 06

18. e = integral measure to recombination=> allows many IGM histories
Combined CMB + GP constraints on reionization
e = integral measure to recombination=> allows many IGM histories
Still a 3 result (now in EE vs. TE before)

19. Pushing into reionization: QSO 1148+52 at z=6.4
tuniv = 0.87Gyr
Lbol = 1e14 Lo
Black hole: ~3 x 109 Mo (Willot etal.)
Gunn Peterson trough (Fan etal.)

20. 1148+52 z=6.42: Gas detection M(H2) ~ 2e10 Mo zhost = 6.419 +/- 0.001
VLA
Off channels
Rms=60uJy
GHz
CO 3-2
IRAM
M(H2) ~ 2e10 Mo
zhost = /
(note: zly = /- 0.04)
VLA

21. Constrain III: Cosmic Stromgren Sphere
Accurate zhost from CO: z=6.419+/0.001
Proximity effect: photons leaking from 6.32<z<6.419
White et al. 2003
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)

22. Loeb & Rybicki 2000

23. 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
Fan et al 2005
P(>xHI)
90% probability
x(HI) > curve
=tqso/4e7 yrs

24. Cosmic Stromgren Surfaces (Hui & Haiman)
zhost
Larger CSS in Ly vs. Ly = Damping wing of Ly?
Large N(HI) (> 1e20cm^-2) => f(HI) > 0.1

25. Difficulties for Cosmic Stromgren Spheres and Surfaces
(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

26. Not ‘event’ but complex process, large variance: zreion ~ 6 to 14 OI
Not ‘event’ but complex process, large variance: zreion ~ 6 to 14
Good evidence for qualitative change in nature of IGM at z~6
ESO

27. Current probes are all fundamentally limited in diagnostic power OI
Saturates, HI distribution function, pre-ionization?
Abundance?
3, integral measure?
Local ionization?
Geometry, pre-reionization?
Local ioniz.?
Current probes are all fundamentally limited in diagnostic power
Need more direct probe of process of reionization = HI 21cm line
ESO

28. Sources responsible for reionization
Luminous AGN: Not. Strong down-turn in luminous AGN population at z>3 (Fan + 06)

29. Sources responsible for reionization
Star forming galaxies: maybe, but need to extrapolate to (not yet observed) dwarf galaxies (Bowens05; Yan04; Stark06)?
Needed for reion.

30. Sources responsible for reionization: other possibilities
Pop III stars z>10? Maybe: possible contribution to fluctuations in the midIR BG (Kashlinsky05)
mini-QSOs -- unlikely due to soft Xray BG limits (Dijkstra04)
Decaying sterile neutrinos -- unlikely (various BGs; Mapelli05)

31. 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

32. HI mass limits => large scale structure
Reionization
1e13 Mo
1e9 Mo

33. HI 21cm radiative transfer: large scale structure of the IGM
LSS: Neutral fraction / Cosmic density / Temperature: Spin, CMB

34. Dark Ages HI 21cm signal Furlanetto et al. 2006
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
T = 2.73(1+z)
TK = 0.026(1+z)^2
Furlanetto et al. 2006

35. Enlightenment and Cosmic Reionization -- first luminous sourcesTK T
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

36. Signal I: Global (‘all sky’) reionization signature
Signal ~ 20mK < 1e-4 sky
Feedback in Galaxy formation
No Feedback
Possible higher z absorption signal via Lya coupling of Ts -- TK due to first luminous objects
Furlanetto, Oh, Briggs 06

37. Signal II: HI 21cm Tomography of IGM Zaldarriaga + 20039
7.6
TB(2’) = 10’s mK
SKA rms(100hr) = 4mK
LOFAR rms (1000hr) = 80mK

38. Signal III: 3D Power spectrum analysis
 only
LOFAR
 + f(HI)
SKA
McQuinn + 06

39. Signal IV: Cosmic Web after reionization
Ly alpha forest at z=3.6 ( < 10)
Womble 96
N(HI) = 1e13 – 1e15 cm^-2, f(HI/HII) = 1e e-6 => before reionization N(HI) =1e18 – 1e21 cm^-2
Lya ~ 1e7 21cm => neutral IGM opaque to Lya, but translucent to 21cm

40. Signal IV: Cosmic web before reionization: HI 21Forest
19mJy
z=12
z=8
130MHz
159MHz
radio G-P (=1%)
21 Forest (10%)
mini-halos (10%)
primordial disks (100%)
Perhaps easiest to detect (use long baselines)
ONLY way to study small scale structure during reionization

41. Radio sources beyond the EOR sifting problem (1/1400 per 20 sq.deg.)
1.4e5 at z > 6
S120 > 6mJy
2240 at z > 6

42. Signal V: Cosmic Stromgren spheres around z > 6 QSOs
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
5Mpc
0.5 mJy
Wyithe et al. 2006

43. 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

44. Challenge I: Low frequency foreground – hot, confused sky
Eberg 408 MHz Image (Haslam )
Coldest regions: T ~ 100 (/200 MHz)^-2.6 K
90% = Galactic foreground
10% = Egal. radio sources ~ 1 source/deg^2 with S140 > 1 Jy

45. Solution: spectral decomposition (eg. Morales, Gnedin…)
Foreground = non-thermal = featureless over ~ 100’s MHz
Signal = fine scale structure on scales ~ few MHz
Cygnus A
10’ FoV; SKA 1000hrs
Signal/Sky ~ 2e-5
500MHz
5000MHz
Simply remove low order polynomial or other smooth function?

46. Cross correlation in frequency, or 3D power spectral analysis: different symmetries in frequency space for signal and foregrounds.
Freq
Foreground
Signal
Morales 2003

47. 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: Jy noise 70 mJy
dynamic range ~ 150,000 : 1

48. 30o x 30o
Galactic foreground polarization ‘interaction’ with polarized beams  frequency dependent residuals! Solution: good calibration of polarization response
NGP MHz 6ox6o ~ 5 K pol
IF Faraday-thin  40 K at 150 MHz
WENSS: Schnitzeler et al A&A Jan07

49. Challenge II: Ionospheric phase errors – varying e- content
TID
74MHz Lane 03
‘Isoplanatic patch’ = few deg = few km
Phase variation proportional to wavelength^2

50. Virgo A 6 hrs VLA 74 MHz Lane + 02
Ionospheric phase errors: The Movie
Solution:
Wide field ‘rubber screen’ phase self-calibration = ‘peeling’
Requires build-up of accurate sky source model
15’
Virgo A 6 hrs VLA 74 MHz Lane + 02

51. 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!

52. Beam nulling -- ASTRON/Dwingeloo (van Ardenne)
Factor 300 reduction in power

53. GMRT Digital Filter in Lag-space (Pen et al. 2007)
150 MHz

54. Leverage: existing telescopes, IF, correlator, operations
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

55. Project abandoned: Digital TV
KNMD Ch 9
150W at 100km

56. RFI mitigation: location, location location…
100 people km^-2
1 km^-2
0.01 km^-2
(Briggs 2005)

57. Multiple experiments under-way: ‘pathfinders’
MWA (MIT/CfA/ANU)
LOFAR (NL)
21CMA (China)
SKA

60. Treion < 450mK at z = 6.5 to 10 (DNR ~ 2700) (expect ~ 20mK)
EDGES (Bowman & Rogers MIT)
All sky reionization HI experiment. Single broadband dipole experiment with (very) carefully controlled systematics + polynomial baseline subtraction (7th order)
VaTech Dipole Ellingson
rms = 75 mK
Sky > 150 K
Treion < 450mK at z = 6.5 to 10 (DNR ~ 2700)
(expect ~ 20mK)

61. GMRT 230 MHz – HI 21cm abs toward highest z (~5.2) radio AGN
S230MHz = 0.5 Jy
GMRT at 230 MHz = z21cm
RFI = 20 kiloJy ! 1”
8GHz Van Breugel et al.
CO Klamer +
M(H2) ~ 3e10 Mo

62. GMRT 230 MHz – HI 21cm abs toward highest z radio AGN (z~5.2)
Limits:
Few mJy/channel
Few percent in optical depth
232MHz 30mJy
229Mhz Jy
rms(40km/s) = 3mJy
rms(20km/s) = 5 mJy
N(HI) ~ 2e20TS cm^-2 ?

63. Focus: Reionization (power spec,CSS,abs)

64. 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

65. PAPERGB -- 8 Ant, 1hr, 12/06 RMS ~ 15Jy; DNR ~ 1e3 CygA 1e4Jy
Cas A 1e3Jy
CygA 1e4Jy
5deg
W44 1e2Jy
HercA 1e2Jy

66. Destination: Moon! 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
RAE2 1973

67. 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

68. Relative evolution of Ly-break (UV continuum) and Ly galaxy populations: Obscuration by the neutral IGM
Two methods for finding very high z galaxies
I. Ly emitters: narrow band search -- affected by IGM abs
850nm => z=5.7
II. Ly-break galaxies: broad band search -- not affected by IGM abs

69. Effect of neutral IGM on LAE vs. LBGz
LAE
UV continuum =
LBG
Barkana and Loeb 2001

70. Local ionization (CSS)? Low S/N
Relative evolution of Ly-break and Ly galaxy populations: Obscuration by the neutral IGM (Ota )
LAE observed z=5.7
LAE predicted z=7 based on UV continuum
At z=7 => f(HI)=0.48+/-0.16
LAE obs z=7
Local ionization (CSS)?
Low S/N

71. END

72. Inverse Compton losses off the CMB
= U_B (radio lobe)

73. Evolution of the neutral IGM (Gnedin): ‘Cosmic Phase transition’
HI fraction
Ionizing intensity
density
Gas Temp
6 Mpc (comoving)

74. Early structure formation: rules-of-thumb (Barkana & Loeb 2002)
Baryons: astrophysics
Dark Matter
Press-Schechter Formalism
M’Jeans’ = 1e4 Msun (z=20)
Minihalos: H2 cooling: Tvir = 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
z M2 Tvir
Msun K
0 1e e7
5 3e e5
6e e3

75. e = integral measure to recombination=> allows many IGM histories
Combined CMB + GP constraints on reionization
e = integral measure to recombination=> allows many IGM histories
Still a 3 result (now in EE vs. TE before)

76. Some basics
Structure formation: the Dark Matter perspective = Press-Schechter Formalism
z M_2s T_vir
M_sun K
0 1e e7
5 3e e5
10 6e e3

77. Structure formation: the Baryons
Some basics
Structure formation: the Baryons
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]

78. Current probes are all fundamentally limited in diagnostic power OI
Saturates, HI distribution function, pre-ionization?
Abundance?
3, integral measure?
Local ionization?
Geometry, pre-reionization?
Local ioniz?
LAE gal
Current probes are all fundamentally limited in diagnostic power
Need more direct probe of process of reionization = HI 21cm line
ESO

79. SDSS QSO CSS => rapid reionization at z~7 ?
ESO