Toward an understanding of foreground emission in the BICEP2 region

By Raphael Flauger, John C. Hill, David N. Spergel. 2014

237 citations recorded by the source corpus.

BICEP2 has reported the detection of a degree-scale B-mode polarization pattern in the Cosmic Microwave Background (CMB) and has interpreted the measurement as evidence for primordial gravitational waves. Motivated by the profound importance of the discovery of gravitational waves from the early Universe, we examine to what extent a combination of Galactic foregrounds and lensed E-modes could be responsible for the signal. We reanalyze the BICEP2 results and show that the 100 ×150 GHz and 150 ×150 GHz data are consistent with a cosmology with r=0.2 and negligible foregrounds, but also with a cosmology with r=0 and a significant dust polarization signal. We give independent estimates of the dust polarization signal in the BICEP2 region using a number of different approaches: (1) data-driven models based on Planck 353 GHz intensity, polarization fractions inferred from the same Planck data used by the BICEP2 team but corrected for CMB and CIB contributions, and polarization angles from starlight polarization data or the Planck sky model; (2) the same set of pre-Planck models used by the BICEP2 team but taking into account the higher polarization fractions observed in the CMB- and CIB-corrected map; (3) a measurement of neutral hydrogen gas column density NHI in the BICEP2 region combined with an extrapolation of a relation between HI column density and dust polarization derived by Planck; and (4) a dust polarization map based on digitized Planck data, which we only use as a final cross-check. While these approaches are consistent with each other, the expected amplitude of the dust polarization power spectrum remains uncertain by about a factor of three. The lower end of the prediction leaves room for a primordial contribution, but at the higher end the dust in combination with the standard CMB lensing signal could account for the BICEP2 observations, without requiring the existence of primordial gravitational waves. By measuring the cross-correlations between the pre-Planck templates used in the BICEP2 analysis and between different versions of a data-based template, we emphasize that cross-correlations between models are very sensitive to noise in the polarization angles and that measured cross-correlations are likely underestimates of the contribution of foregrounds to the map. These results suggest that BICEP1 and BICEP2 data alone cannot distinguish between foregrounds and a primordial gravitational wave signal, and that future Keck Array observations at 100 GHz and Planck observations at higher frequencies will be crucial to determine whether the signal is of primordial origin.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/a72a1aac2444b19f59560ecec0151f936a80278e

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Citations in the corpus

A joint analysis of Planck and BICEP2 B modes including dust polarization uncertainty (2014, methodology): “5×10 20 cm−2 [13], extrapolation using the scaling presented in [11] suggests ∆(2)BB,dust,100 ∼ 0.”
Galaxies as simple dynamical systems: observational data disfavor dark matter and stochastic star formation (2014, background): “Evidence for the predicted inflationary gravitational waves may have been discovered (BICEP2, [16]), although the signal may also be due to the Galactic dust foreground [17, 18].”
Planck2015 results (2015, unknown): “XXX 2016; Mortonson & Seljak 2014; Flauger et al. 2014).”
Causality constraints on corrections to the graviton three-point coupling (2014, background): “At this time, there are alternative explanations for this signal [77, 78], so we might have to wait till the dust settles.”
UltraViolet freeze-in (2014, background): “Recently the BICEP2 collaboration claimed they had observed primordial tensor modes [27], and thus could infer TRH, however this result is currently disputed [28].”
Higgs inflation from Standard Model criticality (2014, background): “It has been pointed out that the BICEP2 result may become consistent with r = 0 because the foreground effect can be sizable [102, 103].”
Cosmic Discordance: Are Planck CMB and CFHTLenS weak lensing measurements out of tune? (2014, background): “…team (BICEP2 Collaboration 2014) have reported a ∼ 5σ detection of the B-mode CMB polarisation signal expected from primordial gravity waves, although whether its origin ? niall.maccrann@gmail.com is cosmological rather than galactic has been disputed (Mortonson & Seljak 2014; Flauger et al. 2014).”