The cosmic evolution of Supermassive Black holes: A panchromatic study of the nuclear environment

超大质量黑洞的宇宙演化：核环境的全色研究

• 批准号: 2773398
• 金额: --
• 依托单位: Newcastle University
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2022
• 资助国家: 英国
• 起止时间: 2022 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2773398
• 关键词: cosmic; evolution; Supermassive; Black; holes

Active Galactic Nuclei or AGN are growing supermassive black holes (SMBH) at the centre of most galaxies in the universe. As one of the most energetic phenomena in the universe, they drive material and energy in and out of their host galaxy, affecting various galaxy properties such as star formation rate, gas temperature, and gas composition. Therefore, understanding the evolution of the AGNs is of great importance for understanding galaxy formation and evolution. Moreover, there is evidence to suggest that galaxies in the early universe (redshift z~2) differ significantly from galaxies in the local universe in terms of their star formation rates (SFR), gas densities, amount of gas, metallicity, etc. Therefore, one may also expect a complementary evolution in AGN and their immediate nuclear environment within galaxies. My project will look for this evolution using the newest telescopes and data analysis techniques.The main way of studying an AGN is by looking at its emission properties. While most of the emitted radiation originates from accretion disk in the close proximity of the SMBH, it interacts with the material surrounding the AGN and as such carries the information about the composition and the geometrical properties of this material. The emission properties are typically represented in form of a spectral energy distribution (SED), the amount of radiation from the source (or part of it) as a function of wavelength, generally measured through a series of photometric filters. Accurate SED modelling is the prime analytic approach of this project.According to the unified model, AGNs are surrounded by dust clouds called the ``obscuring torus'' (or simply ``torus'') spanning 0.1-10 pc from the central SMBH. It also states that different orientations of this torus with respect to the observer's line-of-sight gives rise to various sub-classes of AGNs based on SED shapes. The early ``torus'' models were based on the optical properties of the AGN and had only a few free parameters like orientation of the torus and the luminosity of the source. However, the multi-wavelength studies have hinted that the geometry of this torus is more complex than previously thought. Consequently, these complex models require many more parameters to fully describe the torus, making it difficult to constrain all these parameters at once -- both computationally and theoretically.This difficulty manifests itself in the form of a number of competing phenomena producing emissions at any given wavelength. In order to accurately constrain the torus parameters, it is important to reliably disentangle these phenomena while modelling the SED. The infrared (IR) emission from the AGN is produced when the intrinsic radiation is reddened by interacting with the surrounding dust in the torus. This emission is, however, contaminated by the IR emission from the star forming regions of the host galaxy. With the poor spatial resolution of previous IR observations, it has been difficult to separate these components of SED, and distinguish between various torus models. However, since different emission mechanisms originate from different spatial regions in a galaxy, the high resolution imaging of the source can help in physically separating these emission mechanisms. This will allow us to constrain the torus parameters more precisely and accurately enough to look for the signs of evolution in these parameters over cosmic times. Finding these evolution signatures using high resolution imaging from the James Webb Space Telescope (JWST) and understanding them is the end goal of my PhD project.

活动星系核（AGN）是宇宙中大多数星系中心正在成长的超大质量黑洞（SMBH）。作为宇宙中能量最高的现象之一，它们驱使物质和能量进出其宿主星系，影响星系的各种特性，如恒星形成速度、气体温度和气体成分。因此，了解agn的演化对理解星系的形成和演化具有重要意义。此外，有证据表明，早期宇宙中的星系（红移z~2）与局部宇宙中的星系在恒星形成率（SFR）、气体密度、气体量、金属丰度等方面存在显著差异。因此，人们也可以期待AGN及其在星系内的直接核环境的互补演化。我的项目将使用最新的望远镜和数据分析技术来寻找这种演变。研究AGN的主要方法是观察它的发射特性。虽然大部分发射的辐射来自靠近SMBH的吸积盘，但它与AGN周围的物质相互作用，因此携带了有关该物质的组成和几何特性的信息。发射特性通常以光谱能量分布（SED）的形式表示，来自源（或其一部分）的辐射量作为波长的函数，通常通过一系列光度滤光器来测量。准确的SED建模是本项目的主要分析方法。根据统一模型，agn被尘埃云包围，尘埃云被称为“模糊环面”（或简称为“环面”），距离SMBH中心0.1- 10pc。它还指出，这个环面相对于观察者视线的不同方向会产生基于SED形状的各种agn子类。早期的“环面”模型是基于AGN的光学特性，只有几个自由参数，如环面方向和光源的光度。然而，多波长研究暗示，这个环面的几何形状比以前认为的要复杂得多。因此，这些复杂的模型需要更多的参数来完全描述环面，这使得一次约束所有这些参数变得困难-无论是计算还是理论上。这种困难表现为在任何给定波长产生辐射的许多相互竞争的现象。为了准确地约束环面参数，在对SED建模时可靠地解开这些现象是很重要的。当本征辐射与环面周围的尘埃相互作用而变红时，AGN的红外（IR）发射就产生了。然而，这种辐射被宿主星系恒星形成区域的红外辐射所污染。由于以往红外观测的空间分辨率较差，难以区分SED的这些分量，也难以区分各种环面模型。然而，由于不同的发射机制起源于星系中不同的空间区域，因此源的高分辨率成像可以帮助物理分离这些发射机制。这将使我们能够更精确和准确地约束环面参数，以寻找这些参数在宇宙时间内进化的迹象。利用詹姆斯韦伯太空望远镜（JWST）的高分辨率成像找到这些进化特征并理解它们是我博士项目的最终目标。