Detectability of CMB tensor B modes via delensing with weak lensing galaxy surveys
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104 (United States)
We analyze the possibility of delensing cosmic microwave background (CMB) polarization maps using foreground weak lensing (WL) information. We build an estimator of the CMB lensing potential out of optimally combined projected-potential estimators to different source redshift bins. Our estimator is most sensitive to the redshift depth of the WL survey, less so to the shape noise level. Estimators built using galaxy surveys like the Large Synoptic Survey Telescope and the Supernova Acceleration Probe recover up to 80%-90% of the potential fluctuations power at l{<=}100 but only {approx_equal}10%-20% of the small-angular-scale power (l{<=}1000). This translates into a 30%-50% reduction in the lensing B-mode power. We illustrate the potential advantages of a 21 cm survey by considering a fiducial WL survey for which we take the redshift depth z{sub max} and the effective angular concentration of sources n as free parameters. For a noise level of 1 {mu}K arcmin in the polarization map itself, as projected for a CMBPol experiment, and a beam with {theta}{sub FWHM}=10 arcmin, we find that going to z{sub max}=20 at n=100 galaxies/arcmin{sup 2} yields a delensing performance similar to that of a quadratic lensing potential estimator applied to small-scale CMB maps: the lensing B-mode contamination is reduced by almost an order of magnitude. In this case, there is also a reduction by a factor of {approx_equal}4 in the detectability threshold of the tensor B-mode power. At this CMB noise level, the B-mode detection threshold is only 3x lower even for perfect delensing, so there is little gain from sources with z{sub max}>20. The delensing gains are lost if the CMB beam exceeds {approx}20 arcmin. The delensing gains and useful z{sub max} depend acutely on the CMB map noise level, but beam sizes below 10 arcmin do not help. Delensing via foreground sources does not require arc-minute-resolution CMB observations, a substantial practical advantage over the use of CMB observables for delensing.
- OSTI ID:
- 21024002
- Journal Information:
- Physical Review. D, Particles Fields, Vol. 76, Issue 12; Other Information: DOI: 10.1103/PhysRevD.76.123009; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 0556-2821
- Country of Publication:
- United States
- Language:
- English
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