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Ionised outflows: the missing link in AGN-host galaxy evolution?

电离流出：活动星系核宿主星系演化中缺失的环节？

基本信息

批准号：
PP/D003636/2
负责人：
Alexander Blustin
金额：
$ 14.79万
依托单位：
University of Cambridge
依托单位国家：
英国
项目类别：
Fellowship
财政年份：
2008
资助国家：
英国
起止时间：
2008 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=PP%2FD003636%2F2
关键词：
Ionised outflows missing link AGN

项目摘要

At the heart of most galaxies lies a gigantic black hole with a mass of up to a thousand million Suns. In some nearby galaxies, the gravitational pull of the black hole draws in matter from a rotating disc of gas and dust that surrounds it; before this material is swallowed forever, it loses energy by emitting radiation including visible light, ultraviolet and X-rays. The total energy output of this so-called active galactic nucleus can be greater than that of the whole galaxy that it resides in. Clouds of gas stream away from the nucleus at speeds of several hundred to several thousand kilometres per second. The gas clouds are highly ionised (most of the electrons have been stripped from the atoms) and originate in material blasted out of the black holes's environment by the intense radiation field. It is this radiation which causes the ionisation of the gas. These outflows we see in nearby galaxies could be just the ghostly reminder of a far more dramatic phenomenon at an earlier, violent era in galactic evolution. Increasing attention is now being focused on how ionised outflows connect the evolution of the black hole to that of the surrounding galaxy. While the black hole grows, it is shrouded in gas and dust, obscured from sight. Once the black hole is big enough, the radiation output from accretion can blow away this material, and also matter in the surrounding galaxy that is forming stars. This massive outflow thus ends the process of star formation in the galaxy. Over time, as more and more matter is either consumed by the black hole or driven away in the outflow, the supply of accretion fuel is depleted until the black hole becomes dormant. Ionised outflows from active galactic nuclei are thus central to the development of galaxies and the giant black holes at their cores, and therefore to cosmic evolution as a whole. We study them through the effect they have on the radiation emitted from the active nucleus; radiation at certain energies is absorbed away by the outflowing gas, and by observing the patterns of these absorption features with spectrometers, we can tell how fast the gas is moving, how much gas lies between us and the black hole, and how highly ionised it is. X-ray and ultraviolet radiation from space is mostly prevented from reaching us on the Earth's surface since, fortunately for us, it is absorbed by the atmosphere. We therefore have to study the high energy radiation from deep space objects using telescopes on board satellites in orbit around the Earth, above the screening effects of the atmosphere. My research involves studying, through X-ray spectroscopy with space telescopes, the physical properties of ionised outflows both in nearby and in distant active galaxies (because of the time light takes to reach us, more distant objects probe earlier times in the history of the universe). The ultimate aim is to provide factual information with which to test theories of how the outflow connects the evolution of the black hole and the host galaxy. The key factor in this is determining the rate at which mass is flowing out of the nucleus and into the surrounding galaxy; I will estimate this using physical properties measured from absorption features in X-ray and ultraviolet light. I aim to estimate the mass outflow rates from spectra of active galactic nuclei at a wide range of distances from us, in order to see how the mass outflow rates change over cosmic time. I will then compare the results of this with the history of star formation and the lifecycles of black holes, in order to understand how the ionised outflows connect the evolution of the two.

在大多数星系的中心都有一个巨大的黑洞，其质量高达10亿个太阳。在一些附近的星系中，黑洞的引力从围绕它的气体和尘埃的旋转圆盘中吸引物质;在这些物质被永远吞噬之前，它通过发射包括可见光，紫外线和X射线在内的辐射而失去能量。这个所谓的活动星系核的总能量输出可能大于它所在的整个星系。气体云以每秒几百到几千公里的速度离开原子核。气体云是高度电离的（大部分电子已经从原子中剥离），起源于强烈辐射场从黑洞环境中喷出的物质。正是这种辐射引起气体的电离。我们在附近星系中看到的这些外流可能只是银河系演化早期暴力时代一个更为戏剧性的现象的幽灵般的提醒。现在越来越多的注意力集中在电离流出如何将黑洞的演化与周围星系的演化联系起来。当黑洞成长时，它被气体和尘埃所笼罩，看不见。一旦黑洞足够大，吸积产生的辐射输出可以吹走这些物质，也可以吹走周围星系中正在形成恒星的物质。这一巨大的外流因此结束了星系中星星的形成过程。随着时间的推移，越来越多的物质要么被黑洞消耗，要么在外流中被赶走，吸积燃料的供应被耗尽，直到黑洞进入休眠状态。因此，从活动星系核流出的电离流是星系及其核心巨型黑洞发展的核心，因此也是整个宇宙演化的核心。我们通过它们对活动核发出的辐射的影响来研究它们;某些能量的辐射被流出的气体吸收，通过用光谱仪观察这些吸收特征的模式，我们可以知道气体移动的速度有多快，我们和黑洞之间有多少气体，以及它的电离程度有多高。来自空间的X射线和紫外线辐射大多无法到达地球表面，因为对我们来说幸运的是，这些辐射被大气层吸收了。因此，我们必须利用环绕地球轨道卫星上的望远镜研究来自深空物体的高能辐射，而不受大气层的屏蔽。我的研究涉及通过空间望远镜的X射线光谱学研究附近和遥远的活动星系中电离流出物的物理特性（由于光到达我们所需的时间，更遥远的物体探测宇宙历史上的早期）。最终目的是提供事实信息，以检验流出物如何连接黑洞和宿主星系的演化的理论。其中的关键因素是确定质量从原子核流出并进入周围星系的速率;我将使用从X射线和紫外线吸收特征测量的物理特性来估计这一点。我的目标是从离我们很远的活动星系核的光谱中估计质量流出率，以了解质量流出率如何随宇宙时间变化。然后，我将把这一结果与星星形成的历史和黑洞的生命周期进行比较，以了解电离流出如何将两者的演化联系起来。