Research in astrophysics and cosmology at the University of Bristol

这项建议是为了资助布里斯托尔大学HH Wills物理实验室的研究人员研究天体物理学和宇宙学中的重要问题。过去几年的宇宙学大多建立在对星系团的调查基础上，第一个项目是通过可靠地测量星系团的质量来确保星系团的有效性。这涉及使用几种方法对来自X射线调查的星团样本进行严格的统计调查。星系团的质量范围很广，可以在宇宙年龄的一半以上看到，所以我们还必须考虑到星系团是如何随着时间的变化而变化的。X射线来自星系团持有的热气体大气层--尽管密度较低，但这些大气层占正常物质质量的很大一部分，并有其他可检测到的影响，例如对微波背景辐射的影响。与非X射线质量测量技术的交叉验证将确保我们结果的可靠性。在较小的尺度上，我们知道单个星系也会随时间变化，但目前对这些变化如何依赖于星系质量和环境的了解很少：例如，不同质量的星系变化的速度不同。目前尚不清楚这些过程如何相互作用，以建立我们今天看到的星系群，但我们积累的多波段光学数据可以测试星系如何变化，以及恒星形成是如何在低红移宇宙中形成的。在较高的红移，我们将寻找包含演化最快的星系的原始星系团，以了解星系在第一个大质量结构的早期增长过程中是如何演化的。本质上，所有大质量星系在其中心或其中心附近都包含大质量黑洞，第三个项目将研究此类黑洞如何能够产生强烈的中心辐射源，并将利用这些系统内部不断变化的X射线的亮度和光谱来研究黑洞物理和靠近黑洞的气体。第四个项目研究单个星系中心中靠近中心黑洞的微小区域，可以在大范围内影响气体--通过停止星系团大气的灾难性冷却，并通过在宇宙时间内逐渐使星系团大气变得更具磁性。人们普遍认为，至少在一种加热模式下，星系团中的气体通过从黑洞附近区域喷射出非常热、快速的气体而被重新加热，这一反馈过程被广泛认为是有关的。我们的计算已经确定了负责这种加热的来源的总数，现在想要了解这些对象的过程是如何工作的。第五个项目涉及维护和改进用于处理天文对象目录的代码。这些代码在处理现代天文数据时是必不可少的，并在世界范围内使用，因此对许多天文学家来说非常重要，但需要开发以处理日益增长的天文数据的大小和复杂性。其中一些代码甚至已经进入了微软世界望远镜等公共产品中，另一些代码则在天文学之外找到了创造性的用途。最后一个项目是理论项目，调查行星形成时年轻恒星周围的气体/尘埃盘的性质。当年轻的行星碎片碰撞并聚集成更大的行星时，它们也可以相互摧毁。我们在年轻恒星周围看到的一些尘埃盘可能显示出行星形成的这一破坏性方面的证据。这个项目中高性能计算机计算的目的是解释尘埃盘的极端例子，看看它们是否因为年轻行星之间的巨大碰撞而发生变化。计算的结果将与不断变化的圆盘排放观测结果进行比较。

This proposal is for a grant to researchers in the HH Wills Physics Laboratory of the University of Bristol to investigate important questions in astrophysics and cosmology.Much cosmology over the past few years has been based on investigations of clusters of galaxies, and the first project is to ensure the usefulness of clusters by making reliable measurements of their masses. This involves statistically rigorous investigations using several methods on samples of clusters derived from X-ray surveys. The clusters span a wide mass range and are seen over half the age of the Universe, so we also have to take into account how clusters change in time. The X-rays come from hot gas atmospheres held by the clusters - though low in density these atmospheres account for much of the mass of normal matter, and have other detectable effects, for example on the microwave background radiation. Cross-checks with non-X-ray techniques of mass measurement will ensure the reliability of our results.On a smaller scale, we know that individual galaxies also change in time, but there is currently little understanding of how these changes depend on galaxy mass and environment: galaxies of different masses change at different rates, for example. How these processes act with and against one another to build the population of galaxies that we see today is unclear, but the multi-band optical data that we have accumulated allows tests of how galaxies change, and how star formation is fuelled, in the low-redshift Universe. At higher redshift we will look for proto-clusters, which contain the fastest-evolving galaxies, to understand how galaxies evolve during the early growth of the first massive structures.Essentially all massive galaxies contain massive black holes at, or near, their centres, and a third project will investigate how such black holes are able to create intense central radiation sources, and will use the changing brightness and spectrum of X-rays from the inner parts of these systems to study black hole physics and the gas held close to the black hole.A fourth project looks at how the tiny regions in the centres of individual galaxies, near the central black holes, can affect gas on the large scale - by stopping catastrophic cooling of the atmospheres of clusters of galaxies, and by gradually making cluster atmospheres more magnetic over cosmic time. It is widely believed that a feedback process, in which gas in clusters is reheated by the ejection of very hot, fast, gas from the regions near black holes is involved, at least in one heating mode. Our calculations have identified the population of sources responsible for this heating, and now want to understand how the process works for these objects.The fifth project involves the maintenance and improvement of codes used to work with catalogues of astronomical objects. These codes are essential when dealing with modern astronomical data, and are used world-wide, so are of great importance to many astronomers, but require development to deal with the increasing size and complexity of astronomical data. Some of the codes have even found their way into public products like the Microsoft World-Wide Telescope, and others are finding creative uses beyond astronomy.The final project is theoretical, and investigates the nature of the gas/dust disks around young stars in which planets form. As young pieces of planets collide and assemble into larger planets they can also destroy one another. Some of the dusty disks we see around young stars may show evidence of this destructive side of planet formation. The purpose of the high-performance computer calculations to be done in this project is to interpret the extreme examples of dusty disks to see if they are changing because of giant impacts between young planets. The results from the calculations will be compared with continuing observations of changing disk emission.