Remote Quadrupole Measurements from Reionization

1. Remote Quadrupole Measurements from Reionization Gil Holder Collaborators: Jon Dudley; Alex van Engelen (McGill) Ilian Iliev (CITA/Zurich); Olivier Dore (CITA)

2. Reionization signatures in the CMB Varying z of reionization • Simplest is linear Vishniac effect: free electrons with non-zero velocities and density fluctuations

3. Range in allowed Vishniac effect • Even using the extremely well-constrained cosmological parameters, factor of 3 uncertainty !! • Astrophysical uncertainties comparable…. Dudley-MSc thesis

4. CMB Polarization quadrupoleanisotropy + Thomson scattering =polarization

5. Interplay between Power spectrum reconstruction and reionization studies Primordial power spectrum • Low CMB quadrupole precipitated rash of P(k) reconstruction • Rescattered CMB sourced by P(k) => How well can we measure reionization?

6. Turns out we can measure optical depth pretty well… Top:free-floating P(k) Bottom: Power-law P(k) Constraints on optical depth, allowing nearly arbitrary large scale P(k) (van Engelen MSc thesis) Important for dark energy probes that require an accurate CMB normalization (weak lensing, for example) Van Engelen

7. “Getting around cosmic variance” • Remote quadrupoles from galaxy clusters is an old idea (Kamionkowski & Loeb 1997): • Look for linear CMB polarization from galaxy clusters from scattering of primordial quadrupole • Estimate the optical depth of the cluster and use polarization amplitude and orientation to infer one component of CMB quadrupole as measured at the location of the galaxy cluster • Reionization bubbles have the same optical depth contrast, but are not coincident with a large galaxy cluster (SZ, radio halos, grav. lensing, cluster galaxies, intracluster dust) [10 comoving Mpc at z=9 means 1 physical Mpc at 1000 times current background density]

8. 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 Comoving distance

9. Thomson optical depth/21cm anti-correlation density Thomson optical depth 21cm fluctuations Holder, Iliev & Mellema

10. Some equations… 21 cm fluctuations Optical depth Optical depth fluctuations 21 cm - (optical depth) anti-correlation

11. CMB Pol. & Patchy Reionization • Unlikely to be a problem for inflation B modes • Patchy reionization signal below lensing! • Nearly equal E&B: most of the patchy signal from a narrow range in z

12. Information content of small-scale polarization measurements Raster of CMB polarization measurements yields direct measure of large scale primordial density field (~1000 polarized 1 uK rms measurements spread between z=6 & 15) Dudley-MSc thesis

13. How hard is this? • Need 100 nK in CMB polarization on arcminutes scales (basically ~100 times the collecting area of APEX) for imaging • Need few mK at wavelengths of few m (likely needs SKA) for imaging • Radio point sources will be particularly nasty • Big bubbles around largest sources could have 10x larger signal and detectable with current technology • Stacking of CMB and/or radio data would relax these requirements….

14. Summary • Fine-scale polarization measurements allow large scale Hubble volume mapping at z=1100 • Remote quadrupoles are very hard to measure (sub-uK polarization sensitivity on arcminute scales) • 21cm fluctuations trace optical depth fluctuations remarkably well • Reionization bubbles easier to use than galaxy clusters as scattering centers (same signal amplitude, less confusion)