HI 21cm Signal from Cosmic Reionization

IAU 2006, Long Wavelength Astrophysics

Chris Carilli (NRAO)

Ionized

Neutral

Reionized

Chris Carilli (NRAO)

Berlin June 29, 2005

WMAP – structure from the big bang

Hubble Space Telescope Realm of the Galaxies

Dark Ages

Age of Enlightenment

Epoch of Reionization

•last phase of cosmic evolution to be tested

•bench-mark in cosmic structure formation indicating the first luminous structures

HI 21cm observations of Cosmic Reionization, and beyond

Most direct probe of epoch and process of reionization

Rich in physical diagnostics

Only probe of cosmic evolution during ‘dark ages’

TALK:

Current observational constraints on reionization (Fan et al. ARAA 2006)

Predicted HI 21cm signals

Telescopes and Challenges

Gnedin 03

Reionization: the movie

8Mpc comoving

Constraint I: Gunn-Peterson Effect

Fan et al 2006

End of reionization?

f(HI) > 1e-3 at z = 6.3 vs. <1e-4 at z= 5.7

Fan et al 2003

TT

TE

EE

Constraint II: CMB large scale polarization: Thompson scattering during reionization

Scattered CMBquad. => polarized

Horizon scale => 10’s deg

= 0.09+/-0.03 => z_reion= 11+/3

Page + 06

Current observations => z_reion = 6 to 11?

Not ‘event’ but complex process, large variance time/space

GP => occurs in ‘twilight zone’, opaque _obs< 0.9m

Limitations of current measurements:

CMB polarization

• _e = integral measure through universe=> allows many reionization scenarios

• Still a 3 result (now in EE vs. TE before) Gunn-Peterson effect

• _Lya >>1 for f(HI)>0.001 => low f diagnostic

• to f(HI) conversion requires ‘clumping factor’ (cf. Becker, Rauch, Sargent 2006)

Studying the pristine IGM into the EOR using redshifted HI 21cm observations (100 – 200 MHz)

Large scale structure:

cosmic density,

neutral fraction, f(HI)

Temp: T_K, T_CMB, T_spin

Heating: Ly, Xrays, shocks

)1()10

1)((008.0 2/1

HI

S

CMB fz

T

T

Signal I: Global (‘all sky’) reionization signature in low frequency HI spectra

21cm ‘deviations’ < 1e-4 wrt foreground

Lya coupling: T_spin=T_K < T_CMB

IGM heating: T_spin=T_K > T_CMB

Gnedin & Shaver 03

Signal II: 3D Power spectrum analysis

SKA

LOFAR

McQuinn + 06

only

+ f(HI)

Signal III: HI 21cm Tomography of IGM Zaldarriaga + 2003

z=12 9 7.6

T_B(2’) = 10’s mK

SKA rms(100hr) = 4mK

LOFAR rms (1000hr) = 80mK

N(HI) = 1e13 – 1e15 cm^-2, f(HI/HII) = 1e-5 -- 1e-6

=> Before reionization N(HI) =1e18 – 1e21 cm^-2

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

• expect 0.05 to 0.5 deg^-2 at z> 6 with S_151 > 6 mJy

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: pre-reionization HI signal

eg. Baryon Oscillations (Barkana & Loeb)

Very difficult to detect !

z=50 => = 30 MHz

Signal: 30 arcmin, 50 mk => S_30MHz = 0.1 mJy

SKA sens in 1000hrs:

T_fg = 20000K =>

rms = 0.2 mJy

z=50

z=150

‘Pathfinders’: PAST, LOFAR, MWA, PAPER, …

MWA (MIT/ANU)LOFAR (NL)

PAST (CMU/China)

PAPER Berk/NRAO

Challenge I: Low frequency foreground – hot, confused sky

Eberg 408 MHz Image (Haslam + 1982)

Coldest regions: T = 100z)^-2.6 K

Highly ‘confused’: 1 source/deg^2 with S_0.14 > 1 Jy

All sky: SI deviations = 0.001

Solution: spectral decomposition (eg. Morales, Gnedin…)

10’ FoV; SKA 1000hrs

Power spectral analysis: Fourier analysis in 3D – different symmetries in freq space (ie. Different spectral chan-chan correlation)

Freq

Signal Foreground

TIDs – ‘fuzz-out’ sources

‘Isoplanatic patch’ = few deg = few km

Phase variation proportional to ^2

Solution:

Wide field ‘rubber screen’ phase self-calibration

Challenge II: Ionospheric phase errors – varying e- content

Virgo A VLA 74 MHz Lane + 02

Challenge III: Interference

100 MHz z=13

200 MHz z=6

KNMD Ch 9 Digital TV

Solutions: RFI Mitigation

Digital filtering

Beam nulling

Real-time ‘reference beam’

Solution – RFI mitigation: location, location location…

100 people km^-2

1 km^-2

0.01 km^-2

Destination: Moon!

GMRT 230 MHz – HI 21cm abs toward highest z radio galaxy, 0924-220 z=5.2

rms(20km/s) = 5 mJy

z(CO)

230Mhz 0.5 Jy

8GHz

1”

Van Breugel et al.

RFI = 20 kiloJy !

CO Klamer +

Radio astronomy – Probing Cosmic Reionization

•‘Twilight zone’: study of first light limited to near-IR to radio ’s

• 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

Constraint III: Cosmic Stromgren Spheres

• 1148+5251: Accurate z_host from CO: z=6.419+/0.001

• Proximity effect: photons leaking from 6.32<z<6.419

•‘time bounded’ Stromgren sphere: R = 4.7 Mpc

• f(HI) = 1e-5 R^-3 (t_qso/1e7) yrs

• <f(HI)> ~ 0.1 for sample 19 QSOs at z>5.7 (Fan et al. 06; Wyithe et al. 04)

White et al. 2003