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Cosmic reionization and the history of the neutral intergalactic medium

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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

- 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

Epoch of Reionization

Twilight Zone

- Last phase of cosmic evolution to be tested
- Bench-mark in cosmic

structure formation

indicating the first

luminous structures

Gunn-Peterson Effect toward z~6 SDSS QSOs

Fan et al 2006

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

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

No reionization

Reionization

- Thomson scatting during reionization (z~10)
- Acoustics peaks are ‘fuzzed-out’ during reionization.
- Problem: degenerate with intrinsic amplitude of the anisotropies.

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 nee(1+z)^2 = 0.09+/-0.03

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

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)

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.)

46.6149 GHz

CO 3-2

Off channels

Rms=60uJy

VLA

IRAM

- M(H2) ~ 2e10 Mo
- zhost = 6.419 +/- 0.001

(note: zly = 6.37 +/- 0.04)

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

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)

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

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

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

ESO

Geometry, pre-reionization?

Local ionization?

OI

Abundance?

Saturates, HI distribution function, pre-ionization?

Local ioniz.?

- Current probes are all fundamentally limited in diagnostic power
- Need more direct probe of process of reionization = HI 21cm line

ESO

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

HI 21cm radiative transfer: large scale structure of the IGM

LSS: Neutral fraction / Cosmic density / Temperature: Spin, CMB

- 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

T

Enlightenment and Cosmic Reionization-- first luminous sources

- z ~ 15 to 20: TScouples 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

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

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 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-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 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

sifting problem (1/1400 per 20 sq.deg.)

1.4e5 at z > 6

S120 > 6mJy

2240 at z > 6

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

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 ~ 100 (/200 MHz)^-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

Signal/Sky ~ 2e-5

10’ FoV; SKA 1000hrs

Cygnus A

500MHz

5000MHz

Simply remove low order polynomial or other smooth function?

Crosscorrelation in frequency, or 3D power spectral analysis: different symmetries in frequency space for signal and foregrounds.

Freq

Foreground

Signal

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

Challenge II: Ionospheric phase errors – varying e- content

TID

74MHz Lane 03

- ‘Isoplanatic patch’ = few deg = few km
- Phase variation proportional to wavelength^2

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

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

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)

GMRT 230 MHz – HI 21cm abs toward highest z (~5.2) radio AGN

0924-220 z=5.2

S230MHz = 0.5 Jy

GMRT at 230 MHz = z21cm

RFI = 20 kiloJy !

1”

8GHz Van Breugel et al.

CO Klamer +

M(H2) ~ 3e10 Mo

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

229Mhz0.5 Jy

rms(40km/s) = 3mJy

rms(20km/s) = 5 mJy

N(HI) ~ 2e20TS cm^-2 ?

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

- 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

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

Relative evolution of Ly-break and Ly galaxy populations: Obscuration by the neutral IGM (Ota + 2007)

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

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 = 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

z M2 Tvir

Msun K

0 1e14 3e7

5 3e10 3e5

- 6e7 8e3

Structure formation: the Dark Matter perspective = Press-Schechter Formalism

z M_2s T_vir

M_sun K

0 1e14 3e7

5 3e10 3e5

10 6e7 8e3

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]

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

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

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