CMB Polarization from Patchy Reionization

Gil Holder

Outline

• Patchy reionization

• CMB polarization

• Correlation with redshifted 21cm radiation

• Remote quadrupole measurements & Hubble volume 3D reconstruction

Patchy Reionization

• First stars ``blow bubbles’’ in cosmic web

• Strongly inhomogeneous

• Bubbles growing, becoming more numerous, range in bubble sizes…

Furlanetto et al

CMB Polarization

quadrupoleanisotropy

+ Thomson scattering

=polarization

Polarization from Patchy Reionization

• Very small scales

• Very small signal

Dore et al

CMB Pol. & Patchy Reionization

• Unlikely to be a problem for inflation B modes

• Mainly confined to single Stokes component

Dore et al

Thomson optical depth/21cm anti-correlation

Holder, Iliev & Mellema

Mass density Thomson optical depth

21 cm emission

(slice dz~1; 100 Mpc on a side)

Some equations…

21 cm fluctuations

Optical depth

Optical depth fluctuations

21 cm - (optical depth) anti-correlation

Thomson optical depth/21cm anti-correlation

Holder, Iliev & Mellema

Early times: blowing bubbles (ionize and awe)

Late times: last throes of neutral overdense regions

The benefits of alien collaborators at z~10

• Surface of last scattering at z=10 has little overlap with ours

• More than 1/2 of signal from “dark ages”

• Good enough data over large patch of sky allows reconstruction of “initial conditions” for most of Hubble volume

• Needs polarized 0.1 uK on arcminute scales and mK redshifted 21 cm

Comparison with Galaxy

Clusters

• Z~9 : mean density x1000, comoving 10 Mpc=1 Mpc

• At z=0, this is a galaxy cluster!

• Remote quadrupoles with galaxy clusters suggested by Kamionkowski & Loeb– Z=10 has less overlap with

z=0 CMB– Optical depth from 21cm

instead of ???– No galaxy cluster in the

field (radio halos, AGN, CMB lensing)

SZ Image by Laurie Shaw

How hard is this?

• Need 100 nK in CMB polarization on arcminutes scales (basically 100 times the collecting area of APEX)

• Need few mK at wavelengths of few m (likely needs SKA)

• Radio point sources will be particularly nasty• Big bubbles around largest sources could

have 10x larger signal and detectable with current technology

Summary

• Fine-scale polarization measurements allow new cosmological insights

• Redshifted 21cm emission well anti-correlated with CMB polarization

• Cross-comparison allows measurement of quadrupoles at z~10 (but signals are small)– 21cm gives you optical depth– CMB polarization=optical depth * quadrupole– mK radio signal and 100 nK CMB pol on 1’ scales