[论文解读] Planck intermediate results. XXI. Comparison of polarized thermal emission from Galactic dust at 353GHz with optical interstellar polarization

P. A. R. Ade, N. Aghanim+152 more|arXiv (Cornell University)|May 5, 2014

Diverse Scientific and Engineering Research参考文献 3被引用 4

一句话总结

本研究将普朗克353 GHz亚毫米波尘埃偏振与选定恒星方向的光学星际偏振进行比较，以约束尘埃颗粒的性质。研究发现偏振比RS=V = 4.3 ± 0.2（统计）± 0.4（系统），而相对效率RP=p = 5.6 ± 0.2 MJy sr⁻¹（统计）± 0.4 MJy sr⁻¹（系统）比模型预测高出约2.5倍，表明颗粒对齐与散射模型之间存在关键性矛盾。

ABSTRACT

The Planck survey provides unprecedented full-sky coverage of the submillimetre polarized emission from Galactic dust. In addition to the information on the direction of the Galactic magnetic field, this also brings new constraints on the properties of dust. The dust grains that emit the radiation seen by Planck in the submillimetre also extinguish and polarize starlight in the optical. Comparison of the polarization of the emission and of the interstellar polarization on selected lines of sight probed by stars provides unique new diagnostics of the emission and light scattering properties of dust, and therefore ultimately of the important model parameters, composition, size, shape, and alignment. Using ancillary catalogues of interstellar polarization and extinction of starlight, we obtain the degree of polarization, pV , and the optical depth in the V band to the star, V . We extract the submillimetre polarized intensity, PS, and total intensity, IS, measured toward these stars in the Planck 353 GHz channel. We compare the polarization direction (position angle) measured in the optical with that measured at 353 GHz, and compare the column density measure E(B V) with that inferred from the Planck product map of the submillimetre dust optical depth. For those lines of sight with little CO integrated intensity, as well as having polarization directions close to orthogonal and comparable values of the estimated column density, we correlate the projected polarization e ciencies in emission, QS=IS and US=IS, with those in extinction, qV= V and uV= V , to measure the polarization ratio RS=V = (PS=IS)=(pV= V ). We find a polarization ratio RS=V = 4:3 with statistical and systematic uncertainties 0:2 and 0:4, respectively. We focus directly on the polarization properties of the aligned grain population alone via an alternative ratio, the relative e ciency RP=p = PS=pV = 5:6 MJy sr 1 , with statistical and systematic uncertainties 0:2 and 0:4 MJy sr 1 , respectively. Our estimate of RS=V is reasonably compatible with predictions based on a range of current dust models that have been developed for the di use interstellar medium, not yet very discriminating among them. However, the observed RP=p is a more discriminating diagnostic for the polarizing grain population and is not compatible with predictions, the observations being higher by a factor of about 2.5. These new diagnostics from Planck, including the spectral dependence in the submillimetre, will be important for constraining and understanding the full complexity of the grain models, and for further interpretation of the Planck thermal dust polarization and refining the separation of this contamination of the cosmic microwave background.

研究动机与目标

• 将普朗克的亚毫米波尘埃偏振与光学星际偏振关联，以探究尘埃颗粒的性质。
• 通过将观测到的偏振效率与理论预测进行比较，检验当前的尘埃模型。
• 量化观测到的与模型预测的对齐尘埃颗粒偏振效率之间的差异。
• 改进对尘埃颗粒成分、大小、形状及对齐状态的约束，以用于宇宙微波背景辐射前景分离。
• 为亚毫米波尘埃发射与散射的光谱依赖性提供新的诊断工具。

提出的方法

• 利用普朗克353 GHz全天图提取已知光学偏振的恒星方向的亚毫米波偏振强度（PS）和总强度（IS）。
• 结合V波段消光（AV）和光学偏振度（pV）的辅助星表，推导偏振效率比。
• 计算偏振比RS=V = (PS/IS) / (pV/AV)，以比较发射与消光的偏振效率。
• 定义相对效率RP=p = PS/pV，以独立于总柱密度的方式隔离对齐颗粒的贡献。
• 应用统计与系统误差传播方法，评估RS=V与RP=p的不确定性。
• 聚焦于CO发射较低且偏振位置角正交的视线方向，以最小化污染并增强诊断能力。

实验结果

研究问题

• RQ1 对于同一尘埃群体，亚毫米波发射中的偏振效率与光学消光中的偏振效率相比如何？
• RQ2 当前尘埃模型在多大程度上能预测观测到的偏振比RS=V = (PS/IS)/(pV/AV)？
• RQ3 相对偏振效率RP=p = PS/pV是否与标准尘埃颗粒模型的预测一致？
• RQ4 观测到的RP=p差异对星际尘埃颗粒的对齐与散射特性意味着什么？
• RQ5 亚毫米波偏振的光谱依赖性如何改善对尘埃颗粒模型的约束，并提升宇宙微波背景辐射前景清洁的精度？

主要发现

• 偏振比RS=V = (PS/IS)/(pV/AV) 的测量值为4.3，统计不确定性为0.2，系统不确定性为0.4。
• 相对偏振效率RP=p = PS/pV 的值为5.6 MJy sr⁻¹，统计不确定性为0.2 MJy sr⁻¹，系统不确定性为0.4 MJy sr⁻¹。
• 观测到的RP=p值比当前尘埃模型的预测高出约2.5倍，表明存在显著差异。
• 测量得到的RS=V与现有尘埃模型的预测基本一致，表明在此层次上无强烈冲突。
• 观测到的发射偏振效率高于标准模型的预期，暗示颗粒对齐更强或颗粒性质与假设不同。
• 这些结果为颗粒对齐与散射提供了新的、极具区分力的诊断工具，对改进宇宙微波背景辐射偏振分析与尘埃建模至关重要。