Imaging the Cosmic Web with the Dragonfly Telephoto Array

在过去的40年里，天文成像的前沿已经从地面望远镜的照相底片过渡到空间望远镜的CCD探测器。这使我们探测小星系和微弱星系的能力提高了约600倍。在这段时间里，我们探测宇宙中巨大但微弱（低表面亮度）结构的能力没有任何提高。这是因为在这种情况下，限制因素不是光子统计或图像分辨率，而是对系统误差的控制，例如光的散射和天空变化。我最近与耶鲁大学的一位同事合作，开发了一种新颖的新望远镜，蜻蜓长焦阵列，它成功地突破了这一技术障碍，揭示了宇宙在非常微弱的表面亮度水平上的组成（Abraham &货车Dokkum 2014）。这是一个几乎完全未被探索的天文学领域，在过去的三年里，我们使用这台望远镜（由一系列高端商业长焦镜头构成）来探测宇宙，直到迄今为止不可能微弱的表面亮度水平。人们已经有了许多引人注目的发现，最值得注意的是存在一个新的巨大但微弱的星系群，它们优先居住在丰富的星系团中。这些“超漫射星系”与银河系一样大，但质量只有银河系的1/100 - 1/1000，解释它们的存在是一个主要的难题，已经成为社区调查的一个高度活跃的领域。但这些来自蜻蜓的早期结果只是冰山一角。现在很清楚，低表面亮度的宇宙是一个几乎完全未被探索的天体物理现象的宝库，现在正在进行研究。最令人兴奋的已知超低表面亮度结构是来自“宇宙网”的微弱光致发光，这是一种被认为将星系相互连接的暗物质细丝的预测大规模网络。直接观测宇宙网将是对天空中最大相干结构的里程碑式观测，它将使我们能够直接绘制出局部宇宙中大部分质量的分布。随着这一长期目标的中期，在本提案中，我们要求提供资金，以增加一个原型窄带成像能力的蜻蜓长焦阵列。我们的设计充分利用了Dragonfly的独特优势，但它依赖于未经测试的想法，例如在入射光瞳处的滤波和光束切换。拟议的原型将让我们确定我们的设计，如果我们的超灵敏的窄带成像工程以及在真实的世界，因为它在纸上。如果是这样的话，绘制宇宙网络的地图将在完全升级的蜻蜓长焦阵列的范围内。

Over the past 40 years the cutting edge of astronomical imaging has transitioned from photographic plates on ground based telescopes to CCD detectors on space telescopes. This has improved our ability to detect small and faint galaxies by a factor of about 600. Over this same period of time, there has been no improvement in our ability to detect large but faint (low surface brightness) structures in the Universe. This is because the limiting factor in this case is not photon statistics or image resolution, it is control of systematic errors, such as the scattering of light and sky variability. Working with a colleague at Yale, I recently developed a novel new telescope, the Dragonfly Telephoto Array, which has succeeded in breaking through this technical barrier and which is revealing the composition of the Universe at very faint surface brightness levels (Abraham & van Dokkum 2014). This is an area of astronomy that is almost totally unexplored, and in the last three years we have used this telescope (constructed from an array of high-end commercial telephoto lenses) to probe the Universe down to hitherto impossibly faint surface brightness levels. A number of remarkable discoveries have been made, most notably the existence of a new population of giant but faint galaxies that preferentially inhabit rich galaxy clusters. These "ultra-diffuse galaxies" are as big as the Milky Way but have only 1/100 - 1/1000 of its mass, and explaining their existence is a major puzzle that has turned into a highly active area of investigation by the community. But these early results from Dragonfly are only the tip of the iceberg. It is now clear that the low surface brightness Universe is a treasure trove of almost totally unexplored astrophysical phenomena, and the race is now on to study these. The most exciting known ultra-low surface brightness structure is weak photoluminescence from the "cosmic web", a predicted large scale network of dark matter filaments believed to connect galaxies to each other. Observing the cosmic web directly would be a landmark observation of the largest coherent structure in the sky, and it would let us map out the distribution of most of the mass in the local Universe directly. With this long-term goal in mid, in this proposal we request funding to add a prototype narrow-band imaging capability to the Dragonfly Telephoto Array. Our design fully exploits the unique strengths of Dragonfly, but it relies on untested ideas, such as filtering and beam switching at the entrance pupil. The proposed prototype will let us determine us if our design for an ultra-sensitive narrow-band imager works as well in the real world as it does on paper. If it does, mapping the cosmic web would be within reach of a fully-upgraded Dragonfly Telephoto Array.