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HI 21cm Signal from Cosmic Reionization
IAU 2006, Long Wavelength Astrophysics
Chris Carilli (NRAO)
Ionized
Neutral
Reionized
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Chris Carilli (NRAO)
Berlin June 29, 2005
WMAP – structure from the big bang
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Hubble Space Telescope Realm of the Galaxies
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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
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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
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Gnedin 03
Reionization: the movie
8Mpc comoving
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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
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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
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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
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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)
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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
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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
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Signal II: 3D Power spectrum analysis
SKA
LOFAR
McQuinn + 06
only
+ f(HI)
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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
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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
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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
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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
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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
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‘Pathfinders’: PAST, LOFAR, MWA, PAPER, …
MWA (MIT/ANU)LOFAR (NL)
PAST (CMU/China)
PAPER Berk/NRAO
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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
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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
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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
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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’
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Solution – RFI mitigation: location, location location…
100 people km^-2
1 km^-2
0.01 km^-2
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Destination: Moon!
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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 +
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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
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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