HI 21cm Signal from Cosmic Reionization

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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
Epoch of Reionization
Age of Enlightenment

• 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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Reionization the movie
8Mpc comoving
Gnedin 03
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Constraint I Gunn-Peterson Effect
End of reionization? f(HI) gt 1e-3 at z 6.3
vs. lt1e-4 at z 5.7
Fan et al 2006
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Constraint II CMB large scale polarization
Thompson scattering during reionization

• Scattered CMBquad. gt polarized
• Horizon scale gt 10s deg
• t 0.09/-0.03 gt z_reion 11/3

TT
TE
EE
Fan et al 2003
Page 06
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• Current observations gt z_reion 6 to 11?
• Not event but complex process, large variance
  time/space
• GP gt occurs in twilight zone, opaque l_obs lt
  0.9 mm

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• Limitations of current measurementsCMB
  polarization
• t_e integral measure through universegt
  allows many reionization scenarios
• Still a 3s result (now in EE vs. TE before)
  Gunn-Peterson effect
• t_Lya gtgt1 for f(HI)gt0.001 gt low f(HI)
  diagnostic
• t 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, d
• neutral fraction, f(HI)
• Temp T_K, T_CMB, T_spin
• Heating Lya, Xrays, shocks

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Signal I Global (all sky) reionization
signature in low frequency HI spectra
IGM heating T_spinT_K gt T_CMB
Lya coupling T_spinT_K lt T_CMB
Gnedin Shaver 03
21cm deviations lt 1e-4 wrt foreground
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Signal II 3D Power spectrum analysis
d only
LOFAR
d f(HI)
SKA
McQuinn 06
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Signal III HI 21cm Tomography of IGM
Zaldarriaga 2003
z12
9
7.6

• DT_B(2) 10s mK
• SKA rms(100hr) 4mK
• LOFAR rms (1000hr) 80mK

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Cosmic Web after reionization Ly alpha forest at
z3.6 (d lt 10)
Womble 96
N(HI) 1e13 1e15 cm-2, f(HI/HII) 1e-5 --
1e-6 gt Before reionization N(HI) 1e18 1e21
cm-2
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Signal IV Cosmic web before reionization HI
21Forest
z12
z8
19mJy
130MHz

• radio G-P (t1)
• 21 Forest (10)
• mini-halos (10)
• primordial disks (100)

• expect 0.05 to 0.5 deg-2 at zgt 6 with S_151 gt
  6 mJy

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Signal V Cosmic Stromgren spheres around z gt 6
QSOs

• LOFAR observation
• 20xf(HI)mK, 15,1000km/s
• gt 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 lt T_cmb) signal
  360 mK

5Mpc
0.5 mJy
Wyithe et al. 2006
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Signal VI pre-reionization HI signal eg. Baryon
Oscillations (Barkana Loeb)

• Very difficult to detect !
• z50 gt n 30 MHz
• Signal 30 arcmin, 50 mk gt S_30MHz 0.1 mJy
• SKA sens in 1000hrs
• T_fg 20000K gt
• rms 0.2 mJy

z50
z150
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Pathfinders PAST, LOFAR, MWA, PAPER,
MWA (MIT/ANU)
LOFAR (NL)
PAST (CMU/China)
PAPER Berk/NRAO
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(No Transcript)
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Challenge I Low frequency foreground hot,
confused sky Eberg 408 MHz Image (Haslam 1982)
Coldest regions T 100 (n/200 MHz)-2.6
K Highly confused 1 source/deg2 with S_0.14 gt
1 Jy
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Solution spectral decomposition (eg. Morales,
Gnedin)
10 FoV SKA 1000hrs
All sky SI deviations 0.001
Freq
Signal
Foreground
Power spectral analysis Fourier analysis in 3D
different symmetries in freq space (ie. Different
spectral chan-chan correlation)
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Challenge II Ionospheric phase errors varying
e- content

• TIDs fuzz-out sources
• Isoplanatic patch few deg few km
• Phase variation proportional to l2
• Solution
• Wide field rubber screen phase self-calibration

Virgo A VLA 74 MHz Lane 02
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Challenge III Interference
100 MHz z13
200 MHz z6

• Solutions RFI Mitigation
• Digital filtering
• Beam nulling
• Real-time reference beam

KNMD Ch 9 Digital TV
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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 z5.2
RFI 20 kiloJy !
8GHz
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230Mhz 0.5 Jy
Van Breugel et al.
rms(20km/s) 5 mJy
CO Klamer
z(CO)
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Radio astronomy Probing Cosmic Reionization

• Twilight zone study of first light limited to
  near-IR to radio ls
• First constraints GP, CMBpol gt 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

• 11485251 Accurate z_host from CO
  z6.419/0.001
• Proximity effect photons leaking from
  6.32ltzlt6.419

White et al. 2003

• time bounded Stromgren sphere R 4.7 Mpc
• f(HI) 1e-5 R-3 (t_qso/1e7) yrs
• ltf(HI)gt 0.1 for sample 19 QSOs at zgt5.7
• (Fan et al. 06 Wyithe et al. 04)