Properties of the earliest galaxies

宇宙的宏观宇宙学参数描述了它膨胀的速度以及它的膨胀如何随时间变化，被认为是相当准确的。然而，我们对宇宙的物质并没有深入的了解--暗物质和暗能量主宰着日常生活中常见的普通(‘重子’)物质。我们也不了解导致这种重子物质形成行星、恒星、星系和星系团等结构的过程。由这笔赠款资助的研究的目的是通过观察星系和星系团的形成和演化，以及它们所包含的内部亚结构，来了解影响结构形成的最大规模的现象。星系团的研究通常是通过它们的X射线发射来进行的，X射线发射来自其巨大质量的重力场所持有的热气体。在布里斯托尔，我们也以另一种方式观察气体，通过它在微波背景辐射上投射的‘阴影’，微波背景辐射是在大爆炸后不久产生的一个宇宙辐射场。通过比较这些寻找星团的方法的结果，我们可以知道更多关于气体的信息，也就是关于持有气体的质量的信息，而不是单独使用这两种技术。这一技巧有助于发现星系团中有多少质量是由暗物质组成的，有多少是重子物质，以及星系团质量的这些分量是否有不同的分布。这样的分布差异可能发生在星团形成过程中，当它稳定下来时，或稍后当气体辐射能量时。我们还可以利用我们发现的星系团来研究宇宙本身的膨胀，以更多地了解神秘的暗能量。有一个问题是由星系团辐射的能量引起的--当气体冷却时，它应该向内下降。但我们看到的中央气体太少了--有什么东西在调节流入。人们认为，对气体的一个主要影响，也可能是阻止坠落所需的所有能量的来源，是星系团中心活动星系，特别是射电星系的物质外流。活跃星系是核心似乎有一个非常大质量的黑洞的星系。这些黑洞本身的质量只有一个小星系，而且不知何故能够以接近光速的速度产生远离自身的气体。这有点奇怪，因为我们通常认为黑洞是万物向内坠落的地方，而外流如何工作以及它们产生多少能量的物理原理在很大程度上是未知的。我们需要测量能量，了解这个过程的物理过程，以便了解黑洞是如何影响它们所在的星系团和星系的，我们将在无线电、X射线、星系核心的红外线特性和一些理论上做很多工作，试图了解正在发生的事情。我们希望也能对黑洞本身有更多的了解。星系团最明显的特征是星系本身，我们也有兴趣了解星系是如何形成和随时间变化的，为什么会有不同类型的星系，以及星系是如何影响整个宇宙的。我们发现，最早星系中的恒星释放出足够的辐射，使整个宇宙由冷变热，因此宇宙中的气体从中性原子转变为等离子体，温度与恒星类似。这是如何发生的，以及第一批星系是什么样子，是我们研究的重点。我们还想知道这些早期星系在相互碰撞时发生了什么，它们的恒星老化(可能还会爆炸)，以及它们的中央黑洞不断释放能量，所以我们也观察了附近的星系，以研究宇宙历史上的变化。

The gross cosmological parameters of the Universe that describe how fast it expands and how its expansion changes with time are thought to be known to a fair degree of accuracy. However, we do not have a deep understanding of the material of the Universe - the dark matter and dark energy that dominate over the ordinary ('baryonic') matter that is the familiar stuff of every-day life. We also don't understand the processes that cause this baryonic matter to form into structures such as planets, stars, galaxies, and clusters of galaxies. The purpose of the research to be funded by this grant is to gain some understanding of the largest-scale phenomena that affect the formation of structure by looking at the formation and evolution of galaxies and clusters of galaxies, and the internal substructure that they contain. Clusters of galaxies are often studied by their X-ray emission, which comes from hot gas held by the gravity field of their huge masses. At Bristol we also look at the gas in another way, by the 'shadow' that it casts against the microwave background radiation, which is a universal radiation field that was created soon after the Big Bang. Comparing the results from these ways of finding clusters tells us a lot more about the gas, and so about the mass holding the gas, than either technique alone. This trick is useful for discovering how much mass in the cluster is made up by dark matter and how much is baryonic matter, and whether these components of the mass of the cluster are distributed differently. Such a difference in distribution can occur in the cluster formation process, as it settles into a steady state, or later as the gas radiates energy away. We can also use the clusters that we find to study the expansion of the Universe itself, to find out more about the mysterious dark energy. There is a problem caused by the energy radiated by clusters - as the gas cools, it should drop inwards. But we see too little central gas - something is regulating the infall. It is thought that a major influence on the gas, and perhaps a source of all the energy needed to stop the infall, is the outflow of material from active galaxies, particularly radio galaxies, in the centres of the clusters. Active galaxies are galaxies where there seems to be a very massive black hole at their cores. These black holes themselves have the mass of a small galaxy, and are capable, somehow, of producing flows of gas at close to the speed of light away from themselves. This is a bit strange, since we normally think of black holes as being places where everything falls inwards, and the physics of how the outflows work, and how much energy they produce, is largely unknown. We need to measure that energy, and understand the physics of the process, in order to understand how black holes affect the clusters and galaxies in which they are located, and we will do much work on the radio, X-ray, infra-red properties of galaxy cores, and some theory, to try to understand what is going on. We expect to find out a lot about the black holes themselves, too. The most obvious feature of clusters of galaxies is the galaxies themselves, and we are also interested in knowing how galaxies form and change with time, why there are different types of galaxy, and how the galaxies affect the Universe as a whole. We have found that the stars in the earliest galaxies emit enough radiation to cause the entire Universe to change from being cold to being very hot, so that gas in the Universe changes from being neutral atoms to being a plasma, at a temperature like that of a star. How this happens, and what those first galaxies look like, is a focus of our research. We also want to know what happened to these early galaxies as they collided with one another, as their stars aged (and perhaps exploded), and as their central black holes kept pumping out energy, so we look also at nearby galaxies to study changes over the history of the Universe.