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arXiv 1903.09684astro-ph.GA
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高偏振尘埃区的极端星光偏振

Extreme Starlight Polarization in a Region with Highly Polarized Dust Emission

G. V. Panopoulou, B. S. Hensley, R. Skalidis, D. Blinov, K. Tassis

摘要:

正如普朗克所揭示的那样,银河尘埃的发射在意想不到的高水平上被极化。观测到的$\simeq 20\%$偏振分数的起源可以通过表征具有最大偏振尘埃发射的区域中的光学星光偏振的性质来确定。我们测量了22颗恒星的R波段线偏振,该区域的亚毫米偏振分数为$\simeq 20%$。还在B、V和I波段测量了6颗恒星的子集,以研究偏振的波长依赖性。我们发现,星光在相应的高水平上被偏振。通过多波段偏振测量,我们发现,高偏振分数是不太可能产生不寻常的灰尘属性,如增强晶粒排列。相反,有利的磁场几何形状是最可能的解释,并得到了磁场形态的观测探针的支持。观测到的星光偏振超过了经典的$\left[p_V/E\left(B-V\right)\right]_{\rm max} = 9$ %mag $^{-1}$的上限,并且至少高达13% mag $^{-1}$,这是从普朗克数据、星光偏振和红化测量的联合分析中推断出来的。因此,我们确认,尘埃颗粒在光学波长的内在偏振能力一直被低估。

英文摘要:

Galactic dust emission is polarized at unexpectedly high levels, as revealed by Planck. The origin of the observed $\simeq 20\%$ polarization fractions can be identified by characterizing the properties of optical starlight polarization in a region with maximally polarized dust emission. We measure the R-band linear polarization of 22 stars in a region with a submillimeter polarization fraction of $\simeq 20%$. A subset of 6 stars is also measured in the B, V and I bands to investigate the wavelength dependence of polarization. We find that starlight is polarized at correspondingly high levels. Through multiband polarimetry we find that the high polarization fractions are unlikely to arise from unusual dust properties, such as enhanced grain alignment. Instead, a favorable magnetic field geometry is the most likely explanation, and is supported by observational probes of the magnetic field morphology. The observed starlight polarization exceeds the classical upper limit of $\left[p_V/E\left(B-V\right)\right]_{\rm max} = 9$%mag$^{-1}$ and is at least as high as 13%mag$^{-1}$ that was inferred from a joint analysis of Planck data, starlight polarization and reddening measurements. Thus, we confirm that the intrinsic polarizing ability of dust grains at optical wavelengths has long been underestimated.

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