Theoretical and Observational Cosmology

物理宇宙学是研究宇宙中大尺度结构和演化的科学。这可以分为两大分支：详细研究星系是如何形成和聚集在一起的；以及确定描述整个宇宙的参数。我的研究涉及这两个分支的几个不同部分。在过去的几十年里，我们对宇宙学所了解到的最不寻常的事实是，宇宙的大尺度性质直接服从于观察。这些观测数据的测量精度不断提高，形成了宇宙学中的“标准模型”。这幅图景基于几个简单的假设，提供了一个称为LambdaCDM模型的框架。目前的测量只需要一组六个参数，随着我们收集更多的数据，这些参数的不确定性继续减少。我们知道，宇宙具有接近平面的几何形状，由一种神秘的暗能量主导，大部分物质也是由某种未知的形式组成的。早期宇宙非常平稳，有低幅度的随机相密度扰动，这是在早期宇宙的膨胀图像中产生的那种。我们知道，这些扰动是通过引力不稳定而增长的，从而形成了我们今天在宇宙中看到的所有结构。星系是这种结构的基本组成部分，但星系形成的细节尚不清楚，因为这涉及到各种长度尺度和时间尺度上的巨大物理过程。通常，如果不测量依赖于星系形成和演化的量，就无法测量六个或更多的宇宙学参数。因此，宇宙学的两个主要分支的研究总是紧密相连的。随着参数的测量越来越精确，星系形成的物理过程也越来越详细，我们仍然有许多未解之谜。具体地说：为什么这些参数具有它们所具有的值？什么是暗物质和暗能量？通货膨胀真的发生了吗？我们能从中了解到什么吗？目前标准宇宙学模型中是否缺少一些基本成分？第一批恒星究竟是在什么时候形成的，从而结束了宇宙黑暗时代？宇宙时间内恒星形成的历史是怎样的？星系究竟是如何填充暗物质的光晕的？超大质量黑洞和它们内部形成的星系之间有什么关系？宇宙和我们这一小部分的遥远未来的命运将是什么？宇宙结构的发展是一个复杂的、多方面的话题。解决星系和星系团形成和演化中的最大问题需要观测和理论方法的结合，涵盖整个电磁频谱。一个关键的和发展中的窗口是在亚毫米波段，在那里人们可以很容易地研究非常早期的恒星形成星系，以及星系团中的气体，以及最极端的引力透镜。正因为如此，我参与了几个项目和仪器，这些项目和仪器的重点是使用这些波长，以便进行雄心勃勃的、深入的河外调查。

Physical Cosmology is the study of the structure and evolution of large scales in the Universe. This can be split into two major branches: the detailed study of how galaxies formed and clustered together; and the determination of the parameters which describe the entire Cosmos. My research involves several different parts of both of these branches. The most extraordinary fact that we have learned about cosmology over the last few decades is that the large scale nature of the Universe is directly amenable to observations. These observables have been measured with increasing precision, leading to a "standard model" in cosmology. This picture is based on a few simple assumptions, providing a framework called the LambdaCDM model. Right now the measurements require a set of only six parameters, whose uncertainties continue to decrease as we gather more data. We know that the Universe has close to flat geometry, and is dominated by a mysterious dark energy, with most of the matter also made of some as yet unknown form. The early Universe was very smooth, with low amplitude, random-phase density perturbations, of the sort generated in the inflationary picture of the early Universe. And we know that those perturbations grew through gravitational instability to make all the structure that we seee in the Universe today. Galaxies are the fundamental building blocks of this structure, but the details of galaxy formation are not yet understood, because this involves a huge range of physical processes on a variety of length scales and time scales. Measuring the six or more cosmological parameters cannot typically be done without also measuring quantities that depend on galaxy formation and evolution. Hence the study of the two main branches of cosmology are always intimately connected. With the parameters being measured to greater and greater precision, and the physics of galaxy formation being dissected in ever increasing detail, we are still left with many unsolved puzzles. In particular: why do the parameters have the values that they do? what are the dark matter and the dark energy? did inflation really happen and can we learn anything about it? are some basic ingredients currently missing from the standard cosmological model? when exactly did the first stars form to end the cosmic dark ages? what is the history of star-formation over cosmic time? how exactly do galaxies populate the halos of dark matter? what is the relationship between supermassive black holes and the galaxies that they form inside? what will be the far future fate of the Universe and of our small part of it? The development of structure in the Universe is a complex and multi-faceted topic. Tackling the biggest questions in the formation and evolution of galaxies and clusters of galaxies requires a combination of observational and theoretical approaches, covering the full range of the electromagnetic spectrum. A crucial and developing window is in the sub-millimetre band, where one can readily study star-forming galaxies at very early times, as well as the gas in clusters, and the most extreme gravitational lenses. Because of this I have become involved in several projects and instruments which focus on using these wavelengths in order to conduct ambitious, deep extragalactic surveys.