the cmb as a probe of reionization - university of cambridge · 2011. 7. 29. · the cmb as a probe...
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The CMB as a probe of reionization
Jo Dunkley University of Oxford
High-z July 28 2011
The ‘early’ CMB signal
Linear theory Initial fluctuations evolve, set up
acoustic oscillations Frozen in at last-scattering
WMAP 7-year Larson et al 2011
Electron effect 1: reionization damps the temperature fluctuations for l>40. � Almost degenerate with overall amplitude.
Electron effect 2: CMB polarization
Generated at recombination by viscosity of photon-baryon fluid (E-modes)
Generated at reionization by scattering of CMB quadrupole off electrons
z=1000 z~7 t
WMAP7 polarization
Jarosik et al 2011
TE!
EE!
BB upper limit!
Page et al 2007
WMAP observations E-mode power scales with tau2. 3 year – 6 maps 7 year - 21 maps
Errors on maps halved.
Larson et al 2011
Constraints on tau and z
Optical Depth to reionization: • Tau(7yr) = 0.088 +/- 0.015 (Larson et al 2011) • Tau(5yr) = 0.087 +/- 0.017 (Dunkley et al 2009, adding Ka-band) • Tau(3yr) = 0.089 +/- 0.030 (Spergel et al 2007)
Measure z=10.5 +-1.2 for sudden reionization
(Dunkley et al 2009, updated limits in Larson et al 2011)
Reionization histories
Two-step model, ending at z=7 (Dunkley et al 2009) (Mortonson & Hu 2008)
Standard model, Lewis 2008
Planck: collecting data
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σ(τ)WMAP 7 = 0.015σ(τ)Planck−LFI = 0.010σ(τ)Planck−HFI = 0.005
σ(τ)CV = 0.002
(Planck Blue Book for E-mode power spectrum – assumes white noise)
Armitage-Caplan et al 2010
Constraining history
Planck projected limit on tau>10, Zaldarriaga et al 2009
CMBPol-like limits, Zaldarriaga et al 2009
Small-scale signatures
Velocity of hot electrons from ionization gives kinetic Sunyaev-Zeldovich. Emit isotropically in electron rest frame.
1. Patchy kSZ: fluctuations in delx during reionization (reionization effect 3) 2. Linear OV: linear fluctuations in density and velocity after reionization (reionization effect 4) 3. Non-linear kSZ: non-linear fluctuations from e.g. cluster velocities
[ 4. B-mode polarization from optical depth anisotropy (effect 5, Dvorkin & Smith)]
Moving Electrons
New limits from ACT, SPT
But expected signal very uncertain. Homogeneous reionization: about 2 uK2
Zahn et al 2010 patchy model predicts 3.3 uK2
Predicted signal for sigma8=0.8 universe:
Limits on kinetic SZ power, rule out models with very high reionization kSZ.
SPT: DkSZ < 6.5 µK2 (95% CL)
ACT: DkSZ < 8 µK2 (95% CL)
Shirokoff et al 2011
Dunkley et al 2010
Dunkley et al 2010
kSZ
‘Direct’ detection
1.4°x 1.4° • Will be hard to distinguish patchy signal from OV/kSZ
- Correlate maps with LSS to extract low-z signal
• Size and spectrum of patchy signal would tell us about epoch and scales of bubbles.
• Correlations with 21cm should exist but tricky to see, as kSZ is integrated signal and primary CMB is ‘noise’ (Jelic et al 2009, Tashiro et al 2010)
Summary
• Reionization shows up in CMB in a few ways
- Damping of fluctuations at all scales
- Large-scale polarization signal
- Small-scale OV and patchy reionization signal
• With WMAP we have detected large-scale pol signal, will be able to tell more about optical depth and history from Planck.
• With ACT and SPT we now have much tighter upper limits on the total kSZ signal. Already limits reionization signal! Next, can attempt to distinguish late-time kSZ and patchy reionization signal.