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.