Observational limits on patchy reionization: Implications for B modes
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Publisher:American Physical Society
Citation:Michael J. Mortonson, Wayne Hu, "Observational limits on patchy reionization: Implications for B modes," Physical Review D 81, no. 6 (2010), doi:10.1103/PhysRevD.81.067302
The recent detection of secondary CMB anisotropy by the South Pole Telescope limits temperature fluctuations from the optical depth-modulated Doppler effect to T_3000 < √13μK at multipoles ℓ ∼ 3000. This bound is the first empirical constraint on optical depth fluctuations at arcminute scales, τ_3000=0.001T_3000/μK, implying that these fluctuations are no more than a few percent of the mean. Modulation of the quadrupole source to polarization generates B modes that are bounded as B_3000 = 0.003T_3000. The maximal extrapolation to the ℓ ∼ 100 gravitational wave regime yields B_100 = 0.1T_3000 and remains in excess of gravitational lensing if the comoving size of ionized regions is R ≳ 80 Mpc. If patchy reionization produces much of the observed arcminute scale temperature fluctuations, current bounds on B_100 already require R ≲ 200 Mpc, and limits on both T_3000 and B_100 can be expected to improve rapidly.