Reionization and the CMB

Joanna DunkleyUniversity of Oxford

Ringberg, March 26 2009

The ‘early’ CMB signal

Linear theoryBasic elements have been

understood for 30 years (Peebles, Sunyaev & Zeldovich)

Nolta et al 2009

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~7t

WMAP5 polarization

Hinshaw et al 2009

TE

EE

BB upper limit

Page et al 2007

WMAP observations

(Nolta et al 2009)

Constraints on tau and z

Optical Depth to reionization: • Tau(5yr) = 0.087 +/- 0.017 (Dunkley et al 2009) • Tau(3yr) = 0.089 +/- 0.030 (Spergel et al 2007)Measure z=11.0 +-1.4 for sudden reionization

(Dunkley et al 2009)

Reionization histories

Two-step model, ending at z=7 (Dunkley et al 2009)

(Mortonson & Hu 2008)

Prospects for Planck

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σ(τ )WMAP 5 = 0.017

σ (τ )Planck = 0.005

σ (τ )CV = 0.002

(Planck Blue Book)

(Mortonson & Hu 2008)

Modifications: including helium

• ‘Old’ history (blue dashed)• ‘New’ history (black/red)

• Leads to ~5% reduction in reionization redshift from CMB measurements (delta z~0.5)

• ‘Standard’ history has some width, what to use?

(Lewis 2008)

Small-scale signatures

Velocity of hot electrons from ionization by stars. Emit isotropically in electron rest frame.

1.Linear OV: linear fluctuations in density and velocity from time of reionization (reionization effect 3)2.Non-linear kSZ: non-linear fluctuations from e.g. cluster velocities3.Patchy kSZ: fluctuations in delta_x during reionization (reionization effect 4)

Moving Electrons

Predicted power spectra

(From Zahn et al 2005, in Zaldarriaga et al 2008

CMBPol report)(Iliev, Mellema, Pen, Bond, Shapiro 2008)

CMB

KSZ/OV

Prospects with ACT/SPT1.4°x 1.4°

• Will be hard to distinguish patchy signal from OV/kSZ • Remove non-linear kSZ by identifying clusters• If extract signal, tell us about epoch and scales of bubbles• Could skew cosmological results if ignore

(Iliev et al 2008)

Summary• Reionization shows up in CMB in a few ways

- Damping of fluctuations at all scales l>40

- Large-scale polarization signal

- Small-scale OV signal

- Small-scale 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 can attempt to find OV signal and patchy reionization signal, that will tell us more about reionization epoch.