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?

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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

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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

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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