Research in astrophysics and cosmology at the University of Bristol

这项提案是为布里斯托尔大学HH Wills物理实验室的研究人员提供资助，以研究天体物理学和宇宙学中的重要问题。在过去的几年里，许多宇宙学都是基于对星系团的研究，而第一个项目是通过对星系团的质量进行可靠的测量来确保它们的有用性。这包括使用几种方法对x射线观测得出的星团样本进行统计上严格的调查。这些星系团的质量范围很广，它们的存在时间超过了宇宙年龄的一半，所以我们还必须考虑到星系团是如何随时间变化的。x射线来自星系团所拥有的热气体大气——尽管密度很低，但这些大气占正常物质质量的大部分，并且有其他可探测的影响，例如微波背景辐射。与非x射线质量测量技术的交叉检查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取决于星系质量和环境知之甚少：例如，不同质量的星系以不同的速率变化。这些过程是如何相互作用，相互对抗，从而形成我们今天看到的星系群的，目前还不清楚，但我们积累的多波段光学数据可以测试星系是如何变化的，以及低红移宇宙中恒星形成的燃料是如何形成的。在更高的红移中，我们将寻找包含发展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成长过程中是如何演变的。基本上，所有大质量星系的中心或中心附近都有大质量黑洞，第三个项目将研究这些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x射线的亮度和光谱变化来研究黑洞物理学和靠近黑洞的气体。第四个项目着眼于单个星系中心、靠近中心黑洞的微小区域如何在大尺度上影响气体——通过阻止星系团大气的灾难性冷却，以及通过在宇宙时间内逐渐使星系团大气更具磁性。人们普遍认为，至少在一种加热模式中，参与了一个反馈过程，其中星系团中的气体通过从黑洞附近区域喷出的非常热、快速的气体而重新加热。我们的计算已经确定了造成这种加热的源的数量，现在想了解这个过程是如何对这些物体起作用的。第五个项目涉及维护和改进用于处理天体目录的代码。这些代码在处理现代天文数据时是必不可少的，并且在世界范围内使用，因此对许多天文学家来说非常重要，但需要发展以处理日益增长的天文数据的规模和复杂性。其中一些代码甚至进入了微软全球望远镜（Microsoft worldwide Telescope）等公共产品，还有一些代码正在寻找天文学以外的创造性用途。最后一个项目是理论性的，研究年轻恒星周围形成行星的气体/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，它们也会相互毁灭。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过程中破坏性的一面。在这个项目中，高性能计算机计算的目的是解释尘盘的极端例子，看看它们是否因为年轻行星之间的巨大撞击而发生变化。计算结果将与持续观测的圆盘发射变化进行比较。

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.