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

Lead Research Organisation: Durham University
Department Name: Physics


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.


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