The Formation and Evolution of Galaxies in the Early Universe

宇宙学家长期以来一直试图追溯宇宙从起源到现在的历史。通过对宇宙微波背景辐射的研究，我们获得了最早的宇宙图像，它提供了宇宙40万年前的图像。正是在这个时候，氢——当今最丰富的化学元素——第一次出现了。当时存在的宇宙与我们今天所知的宇宙完全不同。由于整个宇宙中没有一颗恒星，宇宙笼罩在黑暗之中。今天构成我们周围的恒星、行星和生命的普通物质几乎全部包含在氢气中。下一张可用的照片是在宇宙历史上大约10亿年后拍摄的，它揭示了来自单个星系的光，其中一些星系的质量已经是太阳质量的100亿倍。在我们拍摄上一张照片时充满宇宙的氢已经不复存在了。相反，星系之间的空间充满了电子和质子的海洋。这两个时代之间的差距代表了宇宙学最后的未知前沿。在这个未被探索的时代，埋藏着理解第一批恒星和星系是如何形成的关键。我的研究目标是填补宇宙历史上这一重要的缺失章节。天文学家希望解决三个基本问题：1)在最初的10亿年里，第一批恒星和星系是在什么时候出现的？2)是什么摧毁了曾经渗透在星系间空间的氢原子？这是什么时候发生的？3) 10亿年前观测到的大星系的质量是如何聚集在一起的？最近，我在回答其中一些问题方面取得了进展。利用夏威夷的双凯克望远镜，我确定了来自六个星系的光，这些星系似乎是在宇宙只有5亿年的时候发出的。如果这是真的，它将表明这个时代的年轻星系产生足够的辐射能量来分裂星系之间的氢原子。然而，用凯克望远镜验证这些星系确实来自这些非常早期的时期是很困难的。相比之下，在智利的甚大望远镜（VLT）的独特仪器下，确认应该相当简单。如果VLT证明这些星系确实在如此遥远的距离上，那么我们就可以开始测试它们是否与第一代发光物体相对应。此外，我计划在VLT和哈勃太空望远镜（HST）上使用新技术，可以捕捉到5亿年历史的宇宙的更大图像。这些新图片将使我们对年轻宇宙的内容有更深入的了解。最后，我计划研究大爆炸后10到20亿年间大型星系的成长。通过使用HST、斯皮策太空望远镜、VLT和凯克望远镜的观测结果，我可以确定最大的星系是何时形成的，以及它们是否像目前的理论模型所建议的那样，是由许多较小的星系组成的。我在这里描述的每一个项目都带领我们在填补宇宙历史最后缺失的一章的追求中前进。随着新仪器和望远镜的不断发展，我乐观地认为我们很快就会达到我们的目标。

Cosmologists have long sought to trace the history of the universe from its origins to the present day. Our earliest picture of the universe has been secured through the study of the cosmic microwave background which provides a portrait of the universe when it was just 400,000 years old. It was at this time that hydrogen, the most abundant chemical element in the present-day, first came to be. The universe that existed at these times was unlike anything we know of today. With not a single star in all of space, the cosmos was shrouded in darkness. The ordinary matter that today comprises the stars, planets, and life we see around us was almost entirely contained in a gas of hydrogen. The next available picture comes almost one billion years later in cosmic history revealing light from individual galaxies, some already containing a mass ten billion times the mass of our Sun. The hydrogen that filled so much of the universe at the time of our last picture is no longer present. Instead, the space between galaxies is filled with a sea of electrons and protons. The gap between these two epochs represents the final uncharted frontier of cosmology. Buried in this unexplored era are the keys to understanding how the first stars and galaxies came to be. It is the goal of my research to fill in this crucial missing chapter in the history of the cosmos. There are three fundamental questions that astronomers hope to address: 1) At what point over the first billion years did the first stars and galaxies emerge? 2) What destroyed the hydrogen atoms that used to permeate the space between the galaxies and when did this occur? 3) How did the large galaxies that we observe just one billion years assemble their mass? Recently I have made progress in answering some of these questions. Using the twin Keck telescopes in Hawaii, I identified the light from six galaxies which appear to be from when the universe was just 500 million years old. If true, it would indicate that young galaxies from this era produce enough radiant energy to break apart hydrogen atoms between galaxies. However, verifying that these galaxies are indeed from these very early times has proved difficult with the Keck telescopes. In contrast, with the unique instrumentation of the Very Large Telescope (VLT) in Chile, confirmation should be fairly simple. If the VLT proves that the galaxies are indeed at such great distances, then we can begin to test whether they correspond to the first generation of luminous objects. Furthermore, I plan to use new technology on the VLT and on the Hubble Space Telescope (HST) that allows larger images of the 500 million year old universe to be captured. These new pictures should provide us with a much improved understanding of the contents of the young universe. Finally, I plan to study the growth of the large galaxies seen between one and two billion years after the big bang. By using observations from HST, the Spitzer Space Telescope, the VLT, and the Keck telescopes, I can determine when the largest galaxies formed and whether they were built up from many smaller systems, as suggested by current theoretical models. Each of the projects I have described here take us forward in our pursuit of filling in the last missing chapter of cosmic history. With the constant development of new instrumentation and telescopes, I am optimistic that we will soon reach our goal.