Université de Toulouse, UPS-OMP, IRAP, Toulouse, France.
Nature. 2011 Aug 17;476(7360):304-7. doi: 10.1038/nature10320.
High-redshift Lyman-α (Lyα) blobs are extended, luminous but rare structures that seem to be associated with the highest peaks in the matter density of the Universe. Their energy output and morphology are similar to those of powerful radio galaxies, but the source of the luminosity is unclear. Some blobs are associated with ultraviolet or infrared bright galaxies, suggesting an extreme starburst event or accretion onto a central black hole. Another possibility is gas that is shock-excited by supernovae. But not all blobs are associated with galaxies, and these ones may instead be heated by gas falling into a dark-matter halo. The polarization of the Lyα emission can in principle distinguish between these options, but a previous attempt to detect this signature returned a null detection. Here we report observations of polarized Lyα from the blob LAB1 (ref. 2). Although the central region shows no measurable polarization, the polarized fraction (P) increases to ∼20 per cent at a radius of 45 kiloparsecs, forming an almost complete polarized ring. The detection of polarized radiation is inconsistent with the in situ production of Lyα photons, and we conclude that they must have been produced in the galaxies hosted within the nebula, and re-scattered by neutral hydrogen.
高红移莱曼阿尔法（Lyα）云团是延伸的、发光的，但却很罕见的结构，它们似乎与宇宙物质密度的最高峰值有关。它们的能量输出和形态与强大的无线电星系相似，但发光的来源尚不清楚。一些云团与紫外线或红外亮星系有关，这表明存在极端的星暴事件或物质吸积到中心黑洞。另一种可能性是超新星激震的气体。但并非所有的云团都与星系有关，这些云团可能是由落入暗物质晕中的气体加热的。Lyα 发射的偏振在原则上可以区分这些可能性，但之前探测这一特征的尝试结果为零探测。在这里，我们报告了对云团 LAB1 的偏振莱曼阿尔法（Lyα）的观测结果（参考文献 2）。尽管中心区域没有可测量的偏振，但偏振分数（P）在 45 千秒差距的半径处增加到约 20%，形成了一个几乎完整的偏振环。偏振辐射的探测与 Lyα 光子的就地产生不一致，我们得出结论，它们必须是在星云内的星系中产生的，然后被中性氢重新散射。
