BICEP2 / Keck Array VI: Improved Constraints On Cosmology and Foregrounds When Adding 95 GHz Data From Keck Array

TL;DR

This paper combines data from BICEP2, Keck Array, WMAP, and Planck to improve constraints on primordial gravitational waves, dust, and synchrotron foregrounds, setting the tightest limits on the tensor-to-scalar ratio to date.

Contribution

First analysis including 95 GHz Keck Array data, providing the most stringent upper limits on inflationary gravitational waves and foreground contributions.

Findings

Upper limit r_{0.05}<0.09 at 95% confidence

Combined data yields r_{0.05}<0.07 at 95% confidence

No significant evidence for foreground contamination or synchrotron emission

Abstract

We present results from an analysis of all data taken by the BICEP2 & Keck Array CMB polarization experiments up to and including the 2014 observing season. This includes the first Keck Array observations at 95 GHz. The maps reach a depth of 50 nK deg in Stokes $Q$ and $U$ in the 150 GHz band and 127 nK deg in the 95 GHz band. We take auto- and cross-spectra between these maps and publicly available maps from WMAP and Planck at frequencies from 23 GHz to 353 GHz. An excess over lensed-LCDM is detected at modest significance in the 95x150 $BB$ spectrum, and is consistent with the dust contribution expected from our previous work. No significant evidence for synchrotron emission is found in spectra such as 23x95, or for correlation between the dust and synchrotron sky patterns in spectra such as 23x353. We take the likelihood of all the spectra for a multi-component model including lensed-LCDM, dust, synchrotron and a possible contribution from inflationary gravitational waves (as parametrized by the tensor-to-scalar ratio $r$), using priors on the frequency spectral behaviors of dust and synchrotron emission from previous analyses of WMAP and Planck data in other regions of the sky. This analysis yields an upper limit $r_{0.05}<0.09$ at 95% confidence, which is robust to variations explored in analysis and priors. Combining these $B$-mode results with the (more model-dependent) constraints from Planck analysis of CMB temperature plus BAO and other data, yields a combined limit $r_{0.05}<0.07$ at 95% confidence. These are the strongest constraints to date on inflationary gravitational waves.