论文标题
是什么使Ly $α$ Nebulae发光？映射LABD05的极化
What Makes Ly$α$ Nebulae Glow? Mapping the Polarization of LABd05
论文作者
论文摘要
“ ly $α$ nebulae”是巨大的（$ \ sim $ 100 kpc），在遥远的宇宙中发光的气云。他们扩展的$α$排放的起源仍然是一个谜。一些模型认为，当云通过嵌入式或附近的紫外线发射光电离子时，产生了$α$发射，而另一些模型则表明，ly $α$光子来自嵌入式的星系或AGN，然后由云散布。至少在后一种情况下，观察到的$α$发射将是极化的。为了测试这些可能性，我们正在进行七个ly $α$ nebulae的偏光观测。在这里，我们为LABD05提供了结果，该云为$ z $ = 2.656，在Ly $α$排放的峰值的东北部有一个模糊的嵌入式AGN。我们检测到明显的极化。最高的两极分化分数$ p $是$ \ sim $ 10-20％，$ \ sim $ \ sim $ 20-40 kpc ly $α$ peak，远离AGN。最低的$ p $，包括上限，为$ \ sim $ 5％，位于Ly $α$ peak和AGN之间。换句话说，两极分化图被偏转，$ p $从Ly $α$峰增加到东南。测得的极化角$θ$面向东北，大致垂直于$ p $梯度。这种独特的极化模式表明，1）空间偏移的AGN是光电离电气和2）逃脱$α$光子在较大的半径上散布在较大的半径上并进入我们的视线，从而产生了切向导向的，径向增强的，从而使极化远离光电率的区域。最后，我们得出的结论是，气体密度和电离曲线之间的相互作用会产生观察到的$α$发射中的中心峰。这也意味着LABD05的结构比当前理论球形或圆柱模型所假设的更为复杂。
"Ly$α$ nebulae" are giant ($\sim$100 kpc), glowing gas clouds in the distant universe. The origin of their extended Ly$α$ emission remains a mystery. Some models posit that Ly$α$ emission is produced when the cloud is photoionized by UV emission from embedded or nearby sources, while others suggest that the Ly$α$ photons originate from an embedded galaxy or AGN and are then resonantly scattered by the cloud. At least in the latter scenario, the observed Ly$α$ emission will be polarized. To test these possibilities, we are conducting imaging polarimetric observations of seven Ly$α$ nebulae. Here we present our results for LABd05, a cloud at $z$ = 2.656 with an obscured, embedded AGN to the northeast of the peak of Ly$α$ emission. We detect significant polarization. The highest polarization fractions $P$ are $\sim$10-20% at $\sim$20-40 kpc southeast of the Ly$α$ peak, away from the AGN. The lowest $P$, including upper-limits, are $\sim$5% and lie between the Ly$α$ peak and AGN. In other words, the polarization map is lopsided, with $P$ increasing from the Ly$α$ peak to the southeast. The measured polarization angles $θ$ are oriented northeast, roughly perpendicular to the $P$ gradient. This unique polarization pattern suggests that 1) the spatially-offset AGN is photoionizing nearby gas and 2) escaping Ly$α$ photons are scattered by the nebula at larger radii and into our sightline, producing tangentially-oriented, radially-increasing polarization away from the photoionized region. Finally we conclude that the interplay between the gas density and ionization profiles produces the observed central peak in the Ly$α$ emission. This also implies that the structure of LABd05 is more complex than assumed by current theoretical spherical or cylindrical models.
