AGN dust emission as a standard candle in the LSST era

宇宙是由什么构成的？它又是如何变成我们今天看到的样子的？现代宇宙学是在一代又一代试图回答这两个问题的哲学家和科学家的努力下发展起来的。根据我们目前对宇宙的理解，我们知道它始于138亿年前的“大爆炸”，从那以后一直在膨胀。虽然最初非常热，但膨胀使物质冷却，引力作用形成了我们今天看到的恒星和星系。尽管至少从1964年（以大爆炸余辉的发现为标志）以来，这一直是标准的图景，但我们已经意识到，宇宙的两个主要因素是完全未知的：大约85%的物质是看不见的“暗物质”，而不是由我们所知道的原子或基本粒子组成的。在这种巨大的“额外质量”的帮助下，我们可以预期重力最终会减缓大爆炸期间开始的膨胀。然而，在过去的20年里，人们发现了强有力的证据，表明一种未知的力量，即“暗能量”，开始将宇宙拉开，导致宇宙膨胀的速度不断加快。这种暗能量几乎占宇宙能量的70%。那么，这个神秘的黑暗区域背后是什么呢？尽管暗物质和暗能量在观测上是不同的现象，但它们都挑战了我们的物理学基础。会不会是一些我们检验得最好的理论，比如广义相对论，需要在宇宙尺度上重新考虑？这个项目旨在用一种新工具促进宇宙学。我们对宇宙模型的最精确测量来自年轻的宇宙，需要外推到现在。然而，在局部的测量中，今天的宇宙显示出与这些推断相矛盾的迹象。目前还不清楚这种紧张是当前宇宙探测器存在未知问题的事实，还是它们指向有助于我们理解黑暗宇宙的新物理学。大多数直接的宇宙探测器依赖于距离的测量。为此，“标准蜡烛”被调用，其中随着距离变暗的程度与光向我们传播时宇宙的膨胀有关。目前最受欢迎的蜡烛是一种特殊类型的超新星爆炸；然而，它们需要一套复杂的校准来使它们成为局部宇宙学参数的绝对探测器。在这里，一种新型的标准蜡烛将被建立起来，它可以对自己进行校准，并有可能解决不同方法之间宇宙学参数的紧张来自哪里的问题：新的物理学还是未知的错误。这些新的标准蜡烛是星系中心的超大质量黑洞，它们吞噬周围的物质。当物质被吸积时，它被点亮，部分辐射来自一个通用的、标准化的区域，使它成为一个标准的蜡烛。我们将使用计算机模拟和新的观测集来开发这个宇宙学的新工具。我们还将利用这些新数据来解决与超大质量黑洞吸积过程有关的基本问题。

What is the universe made of and how did it come to be as we see it today? Modern cosmology evolved out of generations of philosophers and scientists who tried to answer these two questions. According to our current understanding the universe as we know it started out with a "Big Bang" 13.8 billion years ago and has been expanding ever since. While it was extremely hot initially, the expansion cooled the matter, and gravity worked its way to form stars and galaxies as we see them today.While this has been the standard picture since at least 1964, marked by the discovery of the Big Bang afterglow, we have come to realise that the two dominant factors of the universe are completely unknown: About 85% of the matter is invisible "dark matter" and not formed of the atoms or elementary particles we know of. With the help of this huge "extra mass" we may expect that gravity eventually slows down the expansion that started during the Big Bang. However, over the last 20 years strong evidence has been found that an unknown force, the "dark energy", started pulling the universe apart, leading to an ever increasing rate of expansion. This dark energy accounts for almost 70% of the energy in the universe.So, what is behind this mysterious dark sector? Despite being observationally different phenomena, both dark matter and dark energy challenge our foundation of physics. Could it be that some of our best tested theories, like general relativity, need to be reconsidered on cosmological scales?This project aims at facilitating cosmology with a new tool. Our most precise measurements of the cosmological model come from the young universe and need to be extrapolated to the present. Yet, measurements in the local, present day universe show signs of tension with these extrapolations. It is unclear as of yet if this tension is a fact of unknown problems with the current cosmological probes or if they are pointing towards new physics that will help us understanding the dark universe.Most direct cosmological probes rely on the measurement of distances. For this, "standard candles" are invoked where the degree of dimming with distance relates to the expansion of the universe while the light was travelling to us. The currently most favoured candles are a special type of supernova explosions; however they need a complicated set of calibration to make them absolute probes of the local cosmological parameters. Here a new type of standard candles will be established that can be calibrated against themselves and potentially solve the question where the tension in cosmological parameters between the different methods come from: new physics or unknown errors. These new standard candles are supermassive black holes in the centre of galaxies that swallow matter from its surrounding. As the matter is being accreted, it lights up and part of this radiation comes from a generic, standardised region, making it a standard candle. We will use computer simulations and new sets of observations to exploit this new tool for cosmology. We will also make use of the new data to address fundamental questions related to the accretion process onto supermassive black holes.