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Title: The Signature of Patchy Reionization in the Polarization Anisotropy of the CMB

Abstract

The inhomogeneous ionization state of the universe when the first sources of ionizing radiation appeared should lead to anisotropies in the polarization of the cosmic microwave background. We use cosmological simulations of the process by which the first sources ionized the intergalactic medium to study the induced polarization anisotropies. We find that the polarization anisotropies have rms of order {approx} 0.01 {mu}K, and local peak values of {approx} 0.1 {mu}K, smaller than those due to gravitational lensing on small scales. The polarization direction is highly coherent over degree scales. This directional coherence is not expected from either primary anisotropy or gravitational lensing effects, making the largest signals due to inhomogeneous ionization relatively easy to isolate, should experiments achieve the necessary very low noise levels.

Authors:
; ; ; ; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Stanford Linear Accelerator Center (SLAC)
Sponsoring Org.:
USDOE
OSTI Identifier:
907721
Report Number(s):
SLAC-PUB-12515
astro-ph/0701784; TRN: US200721%%519
DOE Contract Number:
AC02-76SF00515
Resource Type:
Journal Article
Resource Relation:
Journal Name: Submitted to Phys.Rev.D
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ANISOTROPY; IONIZATION; IONIZING RADIATIONS; POLARIZATION; RELICT RADIATION; UNIVERSE; Astrophysics,ASTRO

Citation Formats

Dore, Olivier, /Canadian Inst. Theor. Astrophys., Holder, Gil, /McGill U., Alvarez, Marcelo, /KIPAC, Menlo Park, Iliev, Ilian T., /Canadian Inst. Theor. Astrophys., Mellema, Garrelt, /Stockholm Observ., Pen, Ue-Li, /Canadian Inst. Theor. Astrophys., Shapiro, Paul R., and /Texas U., Astron. Dept. The Signature of Patchy Reionization in the Polarization Anisotropy of the CMB. United States: N. p., 2007. Web. doi:10.1103/PhysRevD.76.043002.
Dore, Olivier, /Canadian Inst. Theor. Astrophys., Holder, Gil, /McGill U., Alvarez, Marcelo, /KIPAC, Menlo Park, Iliev, Ilian T., /Canadian Inst. Theor. Astrophys., Mellema, Garrelt, /Stockholm Observ., Pen, Ue-Li, /Canadian Inst. Theor. Astrophys., Shapiro, Paul R., & /Texas U., Astron. Dept. The Signature of Patchy Reionization in the Polarization Anisotropy of the CMB. United States. doi:10.1103/PhysRevD.76.043002.
Dore, Olivier, /Canadian Inst. Theor. Astrophys., Holder, Gil, /McGill U., Alvarez, Marcelo, /KIPAC, Menlo Park, Iliev, Ilian T., /Canadian Inst. Theor. Astrophys., Mellema, Garrelt, /Stockholm Observ., Pen, Ue-Li, /Canadian Inst. Theor. Astrophys., Shapiro, Paul R., and /Texas U., Astron. Dept. Wed . "The Signature of Patchy Reionization in the Polarization Anisotropy of the CMB". United States. doi:10.1103/PhysRevD.76.043002. https://www.osti.gov/servlets/purl/907721.
@article{osti_907721,
title = {The Signature of Patchy Reionization in the Polarization Anisotropy of the CMB},
author = {Dore, Olivier and /Canadian Inst. Theor. Astrophys. and Holder, Gil and /McGill U. and Alvarez, Marcelo and /KIPAC, Menlo Park and Iliev, Ilian T. and /Canadian Inst. Theor. Astrophys. and Mellema, Garrelt and /Stockholm Observ. and Pen, Ue-Li and /Canadian Inst. Theor. Astrophys. and Shapiro, Paul R. and /Texas U., Astron. Dept.},
abstractNote = {The inhomogeneous ionization state of the universe when the first sources of ionizing radiation appeared should lead to anisotropies in the polarization of the cosmic microwave background. We use cosmological simulations of the process by which the first sources ionized the intergalactic medium to study the induced polarization anisotropies. We find that the polarization anisotropies have rms of order {approx} 0.01 {mu}K, and local peak values of {approx} 0.1 {mu}K, smaller than those due to gravitational lensing on small scales. The polarization direction is highly coherent over degree scales. This directional coherence is not expected from either primary anisotropy or gravitational lensing effects, making the largest signals due to inhomogeneous ionization relatively easy to isolate, should experiments achieve the necessary very low noise levels.},
doi = {10.1103/PhysRevD.76.043002},
journal = {Submitted to Phys.Rev.D},
number = ,
volume = ,
place = {United States},
year = {Wed May 16 00:00:00 EDT 2007},
month = {Wed May 16 00:00:00 EDT 2007}
}
  • The inhomogeneous ionization state of the Universe when the first sources of ionizing radiation appeared should lead to anisotropies in the polarization of the cosmic microwave background. We use cosmological simulations of the process by which the first sources ionized the intergalactic medium to study the induced polarization anisotropies. We find that the polarization anisotropies have rms of order {approx}0.01 {mu}K, and local peak values of {approx}0.1 {mu}K, smaller than those due to gravitational lensing on small scales. The polarization direction is highly coherent over degree scales. This directional coherence is not expected from either primary anisotropy or gravitational lensingmore » effects, making the largest signals due to inhomogeneous ionization relatively easy to isolate, should experiments achieve the necessary very low noise levels.« less
  • B modes in CMB polarization from patchy reionization arise from two effects: generation of polarization from scattering of quadrupole moments by reionization bubbles and fluctuations in the screening of E modes from recombination. The scattering contribution has been studied previously, but the screening contribution has not yet been calculated. We show that on scales smaller than the acoustic scale (l > or approx. 300), the B-mode power from screening is larger than the B-mode power from scattering. The ratio approaches a constant {approx}2.5 below the damping scale (l > or approx. 2000). On degree scales relevant for gravitational waves (lmore » < or approx. 100), screening B modes have a white noise tail and are subdominant to the scattering effect. These results are robust to uncertainties in the modeling of patchy reionization.« less
  • Estimates of inflationary parameters from the CMB B-mode polarization spectrum on the largest scales depend on knowledge of the reionization history, especially at low tensor-to-scalar ratio. Assuming an incorrect reionization history in the analysis of such polarization data can strongly bias the inflationary parameters. One consequence is that the single-field slow-roll consistency relation between the tensor-to-scalar ratio and tensor tilt might be excluded with high significance even if this relation holds in reality. We explain the origin of the bias and present case studies with various tensor amplitudes and noise characteristics. A more model-independent approach can account for uncertainties aboutmore » reionization, and we show that parametrizing the reionization history by a set of its principal components with respect to E-mode polarization removes the bias in inflationary parameter measurement with little degradation in precision.« less
  • The angular power spectrum of the cosmic microwave background temperature anisotropy observed by WMAP has an anomalous dip at l{approx}20 and a bump at l{approx}40. One explanation for this structure is the presence of features in the primordial curvature power spectrum, possibly caused by a step in the inflationary potential. The detection of these features is only marginally significant from temperature data alone. However, the inflationary feature hypothesis predicts a specific shape for the E-mode polarization power spectrum with a structure similar to that observed in temperature at l{approx}20-40. Measurement of the CMB polarization on few-degree scales can therefore bemore » used as a consistency check of the hypothesis. The Planck satellite has the statistical sensitivity to confirm or rule out the model that best fits the temperature features with 3{sigma} significance, assuming all other parameters are known. With a cosmic variance limited experiment, this significance improves to 8{sigma}. For tests of inflationary models that can explain both the dip and the bump in temperature, the primary source of uncertainty is confusion with polarization features created by a complex reionization history, which, at most, reduces the significance to 2.5{sigma} for Planck and 5{sigma}-6{sigma} for an ideal experiment. Smoothing of the polarization spectrum by a large tensor component only slightly reduces the ability of polarization to test for inflationary features, as does requiring that polarization is consistent with the observed temperature spectrum, given the expected low level of TE correlation on few-degree scales. If polarized foregrounds can be adequately subtracted, Planck will supply valuable evidence for or against features in the primordial power spectrum. A future high-sensitivity polarization satellite would enable a decisive test of the feature hypothesis and provide complementary information about the shape of a possible step in the inflationary potential.« less