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了什么角色？在大约10%的星系中，我们观察到由黑洞提供能量的等离子体流出和喷射等高能现象。当一个星系表现出这些特征时，我们称其为活动星系，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，AGN与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AGN反馈是如何工作的细节。对低频无线电发射的观测是查明AGN中正在发生什么的有力工具。这种发射追踪了超大质量黑洞发射的喷流中的相对论电子，以及超大质量黑洞吹向星系的流出物质风。然而，由于它们的低空间分辨率，目前的射电调查很难区分这种活动和恒星形成的射电发射。我的FLF项目通过使用超高空间分辨率无线电观测克服了这一点，这依赖于我为低频阵列（LOFAR）开发的先进校准技术，低频阵列是遍布欧洲的独特无线电天线站阵列。通过只使用部分或全部站点，LOFAR可以是一个更小或更大的“透镜”：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，它可以在视野范围内实现比任何其他类似分辨率射电望远镜大20倍以上的高分辨率，这对于构建了解AGN活动所需的大样本至关重要。我正在进行的FLF项目是制定第一个广域，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。该调查是用所有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视野范围内制作小的高分辨率图像（比标准处理好20倍），并指导了宽视场技术的发展，该技术可以拍摄整个视野，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确定了一个全新的星系样本，其中恒星形成和AGN活动已经同时测量，使用这些高分辨率和标准成像技术的组合；这是同类样本中最大的两个数量级。由此，我们已经了解到AGN在微弱星系中的贡献比以前认为的要高，这对我们理解星系如何形成和演化具有重要意义，该项目将继续量化这一点，以了解AGN在星系演化中的作用。在整个北方天空进行第一次高分辨率的调查将使我能够建立强大的样本，这是同类中最大的，来研究AGN产生无线电发射的物理过程，在星系的大样本中控制这些过程的特性，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，并将该领域推向新的令人兴奋的领域，以回答基本的天体物理学问题。在接下来的几年里，我的工作将为SKA未来的科学调查奠定基础，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，同时将达勒姆和英国置于这一激动人心的科学新革命的前沿。

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.