Black holes: sculptors of galaxies

现代天体物理学中最令人着迷的发现之一是人们认识到，所有大质量星系的中心都有一个黑洞——这些黑洞可能非常巨大，质量很容易超过100万太阳质量。当一个这样的黑洞积极地从周围吸积物质时，它会表现出看似令人困惑的特性。特别是，它可以变得如此明亮，以至于比它的宿主星系更亮，并且它可以驱动强大的外流，通常远远超出星系宿主。流入的吸积物质与通过辐射和流出释放的能量（称为黑洞反馈）之间的相互作用，在塑造黑洞周围环境以及最终形成宿主星系本身方面起着重要作用。然而，人们对这种交换背后的细节仍知之甚少。因此，辨别这一基本过程的本质是现代天体物理学研究的前沿课题。该计划旨在显著提高我们对大质量星系中黑洞反馈的理解。最终目标是建立这种反馈的模型，然后作为宇宙模拟的基本输入。为了实现这一点，我们建立了一个广泛的初步样本，其中包括大范围的有黑洞流出的大质量星系（100个物体）。这个样本的范围从贫血的孤立星系到已知的最大质量星系：那些在星系团中心发现的星系。这些星系都以“x射线空洞”的形式流出——在环绕大质量星系的热晕中耗尽了x射线发射气体的巨大凹坑——由中央黑洞的流出物雕刻而成。这样的目标系统为评估黑洞对周围环境的影响提供了充足的证据。特别是，x射线空腔提供了与黑洞反馈相关的能量学的清晰估计；这是通过对膨胀所需能量的简单计算来确定的。通过利用这个样本，我们将解决三个关键问题，其长期目标是建立一个模型，描述这种反馈在大质量星系中是如何运作的——这个模型将极大地造福于星系外的科学界：(1)我们将确定引起黑洞流出的物理过程是否依赖于星系质量。这就涉及到一些问题，比如，小星系中的流出物实际上是大质量星系中流出物的缩小版吗？如果不是，为什么？AGN的流出是如何依赖于环境影响或宿主星系的特性的？(2)我们将确定黑洞反馈是否以及如何能够通过将富含金属的气体提升到宿主星系之外来丰富星系间介质。这将通过研究流出物周围的元素丰度来实现。量化AGN反馈在重新分配富含金属的气体中所起的作用，对于我们对星系如何形成和演化的总体理解至关重要。(3)我们最终将研究直接来自黑洞的辐射特性，从而深入了解为爆发提供动力的黑洞。这包括建立我们之前在黑洞活动基本平面上的工作，建立x射线光度，射电光度和黑洞质量之间的关系，以及首次建立这些物体的光谱能量分布。该项目将告知我们对黑洞物理学的一般理解，以及对星系外天体物理学和宇宙学的影响。

One of the most fascinating discoveries in modern astrophysics has been the realization that all massive galaxies harbor a black hole at their centers - and that these black holes can be colossal, with masses readily exceeding a million Solar masses. When one such black hole is actively accreting matter from its surroundings, it can exhibit seemingly confounding properties. In particular, it can become so luminous as to outshine its host galaxy, and it can drive powerful outflows that often extend well beyond the galactic host. The interplay between the inflowing accreting matter versus the energy released through radiation and outflows (known as black hole feedback), plays a fundamental role in sculpting the surrounding environment of the black hole, and ultimately the host galaxy itself. Yet the details behind this exchange remain poorly understood. Accordingly, discerning the nature of this fundamental process is a forefront topic of research in modern astrophysics. The proposed program aims to significantly advance our understanding of black hole feedback in massive galaxies. The ultimate goal is to build a model of such feedback, which can then serve as a fundamental input for cosmological simulations. To accomplish this, we have built an extensive preliminary sample that encompasses a large range of massive galaxies with black hole outflows (>100 objects). This sample ranges from anemic isolated galaxies to the most massive galaxies known: those found at the centers of clusters of galaxies. These systems all have outflows in the form of “X-ray cavities” - gargantuan pits which are depleted of X-ray-emitting gas in the hot halos that surround massive galaxies - carved out by the outflows of the central black hole. Such targeted systems provide ample evidence in assessing the impact black holes have on their surrounding environment. In particular, X-ray cavities provide clean estimates for the energetics associated with black hole feedback; this is determined via straightforward calculations of the energy required to inflate them. By utilizing this sample, we will solve three key issues, with the long-term goal of building a model that describes how this feedback operates in massive galaxies - a model that will significantly benefit the extragalactic scientific community: (1) We will determine if the physical processes giving rise to black hole outflows are dependent upon galaxy mass. This touches upon questions such as, are outflows in smaller galaxies actually scaled-down versions of those found in the more massive systems? If not, why? How do AGN outflows depend on environmental effects or on the properties of their host galaxies? (2) We will determine if and how black hole feedback is capable of enriching the intergalactic medium by uplifting metal-rich gas beyond the confines of the host galaxies. This will be achieved by studying the elemental abundances surrounding the outflows. Quantifying the role AGN feedback plays in redistributing metal-rich gas, is vital to our general understanding of how galaxies form and evolve. (3) We will finally study the radiative properties directly arising from the black holes, providing insight into the black holes that power the outbursts. This includes building on our previous work on the fundamental plane of black hole activity, an established relation between X-ray luminosity, radio luminosity, and black hole mass, as well as building for the first time spectral energy distributions for these objects. The program will inform our general understanding of black hole physics, as well as have bearing in extragalactic astrophysics and cosmology.