CMB B-mode polarization from Thomson scattering in the local universe

Journal Article · Tue Mar 15 00:00:00 EST 2005 · Physical Review. D, Particles Fields

DOI:https://doi.org/10.1103/PhysRevD.71.063531· OSTI ID:20706198

Hirata, Christopher M ^[1]; Loeb, Abraham; Afshordi, Niayesh ^[2]

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1. Department of Physics, Jadwin Hall, Princeton University, Princeton, New Jersey 08544 (United States)
2. Harvard-Smithsonian Center for Astrophysics, MS-51, 60 Garden Street, Cambridge, Massachusetts 02138 (United States)

The polarization of the cosmic microwave background (CMB) is widely recognized as a potential source of information about primordial gravitational waves. The gravitational wave contribution can be separated from the dominant CMB polarization created by density perturbations at the times of recombination and reionization because it generates both E and B polarization modes, whereas the density perturbations create only E polarization. The limits of our ability to measure gravitational waves are thus determined by statistical and systematic errors from CMB experiments, foregrounds, and nonlinear evolution effects such as gravitational lensing of the CMB. Usually it is assumed that most foregrounds can be removed because of their frequency dependence, however Thomson scattering of the CMB quadrupole by electrons in the Galaxy or nearby structures shares the blackbody frequency dependence of the CMB. If the optical depth from these nearby electrons is anisotropic, the polarization generated can include B modes even if no tensor perturbations are present. We estimate this effect for the Galactic disk and nearby extragalactic structures, and find that it contributes to the B polarization at the level of {approx}(1-2)x10{sup -4} {mu}K per logarithmic interval in multipole l for l<30. This is well below the detectability level even for a future CMB polarization satellite and hence is negligible. Depending on its structure and extent, the Galactic corona may be a source of B-modes comparable to the residual large-scale lensing B-mode after the latter has been cleaned using lensing reconstruction techniques. For an extremely ambitious post-Planck CMB experiment, Thomson scattering in the Galactic corona is thus a potential contaminant of the gravitational wave signal; conversely, if the other foregrounds can be cleaned out, such an experiment might be able to constrain models of the corona.

• OSTI ID: 20706198
• Journal Information: Physical Review. D, Particles Fields, Vol. 71, Issue 6; Other Information: DOI: 10.1103/PhysRevD.71.063531; (c) 2005 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 0556-2821
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
ANISOTROPY
COSMIC RADIATION
COSMOLOGY
DENSITY
DISTURBANCES
ELECTRONS
FREQUENCY DEPENDENCE
GALAXIES
GRAVITATIONAL LENSES
GRAVITATIONAL WAVES
NONLINEAR PROBLEMS
POLARIZATION
POTENTIALS
QUADRUPOLES
RADIOWAVE RADIATION
RELICT RADIATION
TENSORS
THOMSON SCATTERING
UNIVERSE