AGN dust emission as a standard candle in the LSST era

宇宙是由什么组成的，它是如何变成我们今天所看到的样子的？现代宇宙学是从几代哲学家和科学家试图回答这两个问题中发展出来的。根据我们目前的理解，我们所知道的宇宙始于138亿年前的“大爆炸”，并从那时起一直在膨胀。虽然它最初非常热，但膨胀冷却了物质，引力以其自身的方式形成了我们今天看到的恒星和星系。虽然这至少是自1964年以来的标准图片，以大爆炸余辉的发现为标志，但我们已经意识到宇宙的两个主导因素是完全未知的：大约85%的物质是不可见的“暗物质”，不是由我们所知道的原子或基本粒子形成的。在这个巨大的“额外质量”的帮助下，我们可以预期引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，强有力的证据表明，一种未知的力量，“暗能量”，开始将宇宙拉开，导致膨胀率不断增加。这种暗能量几乎占宇宙能量的70%。那么，这个神秘的暗区背后是什么呢？尽管是观测上不同的现象，暗物质和暗能量都挑战了我们的物理学基础。会不会是我们的一些最好的理论，比如广义相对论，需要在宇宙学的尺度上重新考虑？该项目旨在用一种新工具促进宇宙学。我们对宇宙学模型最精确的测量来自年轻的宇宙，需要外推到现在。然而，在当地的测量，今天的宇宙显示出紧张的迹象与这些推断。目前还不清楚这种张力是当前宇宙学探测器的未知问题的事实，还是它们指向新的物理学，帮助我们理解暗宇宙。大多数直接的宇宙学探测依赖于距离测量。为此，“标准蜡烛”被调用，其中随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，使它们成为局部宇宙学参数的绝对探测器。在这里，将建立一种新型的标准烛光，可以对它们进行校准，并可能解决不同方法之间宇宙学参数的紧张关系来自哪里的问题：新物理或未知的错误。这些新的标准烛光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，它会发光，部分辐射来自一个通用的标准化区域，使其成为一个标准蜡烛。我们将使用计算机模拟和新的观测集来利用这一新的宇宙学工具。我们还将利用新数据来解决与超大质量黑洞吸积过程相关的基本问题。

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.