Toward an understanding of foreground emission in the BICEP2 region
Toward an understanding of foreground emission in the BICEP2 region
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DOI：
10.1088/1475-7516/2014/08/039
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发表时间：
2014-05
影响因子：
6.4
通讯作者：
R. Flauger;R. Flauger;J. Hill;D. Spergel
中科院分区：
文献类型：
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作者：
R. Flauger;R. Flauger;J. Hill;D. Spergel
BICEP 2报告了在宇宙微波背景（CMB）中探测到度尺度的B模式偏振模式，并将测量结果解释为原始引力波的证据。出于对早期宇宙引力波发现的深刻重要性的认识，我们研究了银河系前景和透镜E模式的组合在多大程度上可能对信号负责。我们重新分析了BICEP 2的结果，发现100 ×150 GHz和150 ×150 GHz的数据与r=0.2的宇宙学和可忽略的前景一致，但也与r=0的宇宙学和显著的尘埃偏振信号一致。我们用几种不同的方法对BICEP 2区域的尘埃偏振信号进行了独立的估计：（1）基于普朗克353 GHz强度的数据驱动模型，从BICEP 2团队使用的相同普朗克数据中推导出的偏振分数，但对CMB和CIB的贡献进行了校正，以及从星光偏振数据或普朗克天空模型中推导出的偏振角;（2）与BICEP 2小组使用的前普朗克模型相同，但考虑到CMB和CIB校正图中观察到的更高的极化分数;（3）BICEP 2区域中性氢气柱密度NHI的测量，结合普朗克导出的HI柱密度和尘埃极化之间关系的外推;（4）基于数字化普朗克数据的尘埃偏振图，我们只将其用作最后的交叉检查。虽然这些方法是相互一致的，尘埃偏振功率谱的预期幅度仍然不确定的约三个因素。预测的低端为原始贡献留下了空间，但在高端，尘埃与标准CMB透镜信号的结合可以解释BICEP 2的观测结果，而不需要原始引力波的存在。通过测量BICEP 2分析中使用的前普朗克模板之间的互相关和基于数据的模板的不同版本之间的互相关，我们强调，模型之间的互相关对偏振角中的噪声非常敏感，并且测量的互相关可能低估了前景对地图的贡献。这些结果表明，BICEP 1和BICEP 2数据本身无法区分前景和原始引力波信号，未来在100 GHz的凯克阵列观测和更高频率的普朗克观测对于确定信号是否是原始起源至关重要。
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.