Joint Analysis of BICEP2/Keck Array and Planck Data

March 10, 2015
Figure 1

Fig 1: Planck 353 GHz T, Q, and U maps before (left) and after (right) the application of BICEP2/Keck filtering.

The results of the joint analysis of BICEP2/Keck Array and Planck Collaborations have been published in the latest issue of Physical Review Letter*. BICEP2 and Keck Array have observed the same approximately 400 deg2 patch of sky centered on RA 0 h, Dec. −57.5°. The combined maps reach a depth of 57 nK deg in Stokes Q and U in a band centered at 150 GHz. Planck has observed the full sky in polarization at seven frequencies from 30 to 353 GHz, but much less deeply in any given region ( 1.2 μK deg in Q and U at 143 GHz). They detected 150×353 cross-correlation in B modes at high significance.

The teams fit the single- and cross-frequency power spectra at frequencies ≥150 GHz to a lensed-Λ CDM model that includes dust and a possible contribution from inflationary gravitational waves (as parametrized by the tensor-to-scalar ratio r), using a prior on the frequency spectral behavior of polarized dust emission from previous Planck analysis of other regions of the sky. They found strong evidence for dust and no statistically significant evidence for tensor modes. They further probed various model variations and extensions, including adding a synchrotron component in combination with lower frequency data, and found that these make little difference to the r constraint. Finally, they presented an alternative analysis which is similar to a map-based cleaning of the dust contribution, and showed that this gives similar constraints. The final result is expressed as a likelihood curve for r, and yields an upper limit r0.05 < 0.12 at 95% confidence. Marginalizing over dust and r, lensing B modes are detected at 7.0σ significance.


*P.A.R. Ade, et al. (BICEP2/Keck and Planck Collaborations), "Joint Analysis of BICEP2/Keck Array and Planck Data," Phys. Rev. Lett. 114, 101301 (9 Mar 2015) DOI: http://dx.doi.org/10.1103/PhysRevLett.114.101301.