Zooming in on feedback in active galaxies: The first high-resolution radio survey

几乎每个大质量星系的中心都存在一个超大质量黑洞，但它们在星系演化中扮演着什么角色呢？在大约10%的星系中，我们观察到了由这些黑洞提供能量的等离子体流出和喷射等能量现象。当一个星系表现出这些特征时，我们称之为活动星系，并将黑洞及其能量输出称为活动星系核(AGN)。我们从观测和宇宙学模拟中都知道，活动星系核和其宿主星系之间的反馈可以对该星系的演化产生重大影响。我们不知道的是活动星系核反馈如何工作的细节。对低频射电发射的观测是精确定位活动星系核正在发生的事情的有力工具。这种发射追踪由超大质量黑洞发射的喷流中的相对论电子，以及由超大质量黑洞吹到银河系的外流物质的风。然而，由于空间分辨率较低，目前的射电测量很难区分这一活动和恒星形成过程中的射电发射。我的FLF项目通过使用超高空间分辨率的无线电观测来克服这一点，这依赖于我为低频阵列(LOFAR)开发的先进校准技术，LOFAR是分布在欧洲各地的独特的无线电天线站阵列。LOFAR可以是一个更小的或更大的‘镜头’，只使用一些或所有的站：我们使用的越多，可以达到的分辨率就越高，但这需要专门的校准技术。LOFAR的独特之处在于，它可以在比任何其他类似分辨率射电望远镜大20倍的视场内实现高分辨率，这对于建立理解活动星系核活动所需的大样本至关重要。我正在进行的FLF项目是制定第一个大范围、高分辨率的调查。我是通过对LOFAR两米巡天(LoTSS)的数据进行后处理来做到这一点的。这项调查是用所有LOFAR天线记录的，但标准处理只使用位于荷兰的天线，分辨率较低。我已经证明了我们可以在整个视场中制作小的高分辨率图像(&gt；比标准处理好20倍)，并指导了广域技术的发展，这些技术可以成像整个视场，尽管计算成本很高。使用这些令人兴奋的新图像，我的初步科学成果包括识别一个全新的星系样本，其中恒星形成和活动星系核的活动已经通过这些高分辨率和标准成像技术的组合进行了同时测量；这是同类样本中最大的两个数量级。从这一点上，我们已经了解到活动星系核在暗星系中的贡献比之前认为的要高，这对我们理解星系的形成和演化具有重要意义，这个项目将继续量化这一点，以了解活动星系核在星系演化中的作用。进行第一次跨整个北方天空的高分辨率调查将使我能够建立强大的样本，这是同类调查中最大的，以研究活动星系核产生射电发射的物理过程，在大样本星系中这些过程是什么性质的，以及这些过程如何通过恒星形成影响星系的典型增长。我将通过我的UKRI-FLF项目推动AGN反馈研究的重大进展，并在回答基本天体物理问题方面将该领域推向新的令人兴奋的领域。在接下来的几年里，我的工作将为英国在SKA进行的未来科学调查奠定基础，英国在这方面投入了大量资金。我将继续与南非、荷兰和印度的SKA探路者团队开展国际合作，同时将达勒姆大学和英国置于这场激动人心的新科学革命的前沿。

A super-massive black hole exists at the centre of almost every massive galaxy, but what role do they play in galaxy evolution? In about 10 percent of all galaxies, we observe energetic phenomena like outflows and jets of plasma that are powered by these black holes. When a galaxy shows these characteristics we call it an active galaxy, and refer to the black hole and its energetic output as an active galactic nucleus (AGN). We know from both observations and cosmological simulations that feedback between an AGN and its host galaxy can have a significant impact on that galaxy's evolution. What we do not know are the details of how this AGN feedback works.Observations of low-frequency radio emission are a powerful tool to pinpoint what is happening in AGN. This emission traces relativistic electrons in jets launched by a super-massive black hole and winds of outflowing material blown out into the galaxy by the super-massive black hole. However, due to their low spatial resolution, current radio surveys have difficulty distinguishing between this activity and radio emission from star formation. My FLF project overcomes this by using ultra-high spatial resolution radio observations, which rely on advanced calibration techniques I developed for the LOw Frequency ARray (LOFAR), a unique array of radio antenna stations spread across Europe. LOFAR can be a smaller or a bigger 'lens' by using only some or all of the stations: the more we use, the higher the resolution that can be achieved, but this requires specialised calibration techniques. LOFAR is unique in that it can achieve high resolution across a field of view more than 20 times larger than any other similar resolution radio telescope, which is critical to build the large samples necessary to understand AGN activity.My ongoing FLF project is to enact the first wide area, high resolution survey. I am doing this by post-processing data from the LOFAR Two-metre Sky Survey (LoTSS). The survey is recorded with all LOFAR antennas, but standard processing only uses those located in the Netherlands, providing lower resolution. Already I have demonstrated that we can make small high-resolution images (>20 times better than the standard processing) across the field of view, and guided the development of wide-field techniques that image the full field of view, although at a high computational cost.Using these exciting new images, my initial scientific results include identifying an entirely new sample of galaxies where star formation and AGN activity have been simultaneously measured using a combination of these high-resolution and standard imaging techniques; this is the largest sample of its kind by two orders of magnitude. From this, we are already learning that the AGN contribution in faint galaxies is higher than previously thought, with implications for our understanding of how galaxies form and evolve, and this project will continue to quantify this to understand the role of AGN in galaxy evolution.Conducting the first high-resolution survey across the entire Northern sky will allow me to build robust samples, the largest of their kind, to study the physical processes by which AGN produce radio emission, what properties govern these processes across large samples of galaxies, and how these processes impact the typical growth of galaxies through star formation. I will drive forward major advances in AGN feedback studies with my UKRI-FLF project, and push the field to new and exciting territory in answering fundamental astrophysical questions.Over the next several years, my work will lay the foundation for future scientific surveys with the SKA, in which the UK has heavily invested. I will continue to develop international collaborations with SKA pathfinder teams in South Africa, the Netherlands, and India, while placing Durham and the UK at the forefront of this exciting new revolution in science.