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

Lead Research Organisation: Durham University
Department Name: Physics

Abstract

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 ouput 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.

Current AGN feedback studies rely on indirect evidence and focus on individual objects or small samples. It can be extremely difficult to tell the difference between star formation, which is how galaxies normally grow, and AGN activity. High resolution imaging can help, and at radio wavelengths this alone is enough to clearly distinguish between AGN activity and star formation. Traditionally radio telescopes with high enough resolution to do this have tiny fields of view which limits studies to small numbers of galaxies.

The advent of next-generation of low-frequency radio telescopes offers a new and exciting way to overcome this challenge. This relies on combining both wide-field and high-resolution capabilities of the LOw Frequency ARray (LOFAR), using techniques I have developed. LOFAR is a Square Kilometre Array (SKA) pathfinder with antennas spread all across Europe. Default operations use only the antennas centred in the Netherlands, but I have developed a high-resolution imaging data pipeline to combine signals from all the antennas in the array, providing a larger effective 'lens' and 20 times improved resolution.

My high-resolution work is opening a new regime for radio surveys, and I hold the record for the highest resolution image ever made below 100 MHz (just below the FM radio band). My ambitious and exciting UKRI FLF project is to conduct the first high-resolution survey across the entire Northern sky, which will allow me 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. This survey will build from smaller datasets on interesting areas of sky with exquisite coverage across radio, infrared, optical, and X-ray wavelengths, and eventually cover the entire Northern sky.

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. Dealing with such large data volumes will feed into the general trend for developing tools and techniques to deal with Big Data. I will exploit opportunities for interdisciplinary science, including working with computer scientists to develop new algorithms for identifying and classifying the radio emission from AGN in large surveys. In the next few years, my work will lay the foundation for future scientific surveys with the SKA, in which the UK has already invested £119 million. I will build international collaborations with SKA pathfinder teams in South Africa, the Netherlands, and place Durham and the UK at the forefront of this exciting new revolution in science.

Planned Impact

The key impact goals of this research are:
(1) To increase our fundamental knowledge of how the Universe was shaped by super-massive black holes
(2) To employ new data processing methods which push the boundaries of national/international facilities
(3) To retain skills and knowledge in the UK which will contribute to the nation's scientific and economic competitiveness
(4) To provide high-profile innovative research and broaden the public perception of who can be a scientist

The stakeholders who will most directly benefit from (1) and (2) are the academic and public sectors. This includes the general public, through outreach activities, media attention, and citizen science projects during this fellowship project. The results will be presented in a format suitable for the public on the project website long after the fellowship ends. The academic sector will benefit directly from the scientific advancements of this study, both during the fellowship and building on its successes in the future.

Both direct and indirect impact for a wide range of sectors will come from (2) and (3) in terms of preparing for the Square Kilometre Array (SKA), which is a global organisation with headquarters at Jodrell Bank in the UK. The methodology and technical skills I have developed in my research will help shape how the SKA data processing infrastructure is built and used, which will have direct and indirect impacts across the commercial / private sector, and for the policy makers at an international level. By performing SKA-type science before the SKA, I have a unique opportunity to impact the decision making process by understanding exactly what challenges we will face with the SKA and how to best overcome them. In addition to guiding concrete logistical decisions, this will help foster an excellent global collaboration within the SKA, and specifically promote the UK contribution.

Finally, by establishing myself as a scientific leader in the UK, I will indirectly impact the UK public with (3) and (4). In particular, I will help shape the scientific landscape in the UK with my cutting edge research. My non-standard background includes a previous career in the military, and my unique science-related sewing is featured online and has been displayed in a scientific art exhibition. When coupled with my successful, innovative science, I aim to challenge the public perception of what it takes to be a scientist and help break down barriers for underrepresented minorities, particularly women, in Science, Technology, Engineering, and Mathematics (STEM) career fields.

Publications

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Callingham J (2023) V-LoTSS: The circularly polarised LOFAR Two-metre Sky Survey in Astronomy & Astrophysics

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De Gasperin F (2021) The LOFAR LBA Sky Survey I. Survey description and preliminary data release in Astronomy & Astrophysics

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Delhaize J (2021) MIGHTEE: are giant radio galaxies more common than we thought? in Monthly Notices of the Royal Astronomical Society

 
Description Looking at galaxies with radio frequencies reveals a completely different picture than in optical images: instead of starlight, we see radio emission generated by the birth of stars, and sometimes we see radio emission that comes from activity related to super-massive black holes that "feed" on their host galaxies. To understand how these super-massive black holes can impact the birth of stars in galaxies, we have to be able to separate this radio emission, which can be done using ultra-high resolution radio images. As part of my fellowship work, I have for the first time been able to do this at low radio frequencies with the International LOFAR Telescope (ILT), which has the advantage of more than 20 times the field of view as radio telescopes at high frequencies. Using a new 7 billion pixel image from ILT data with high resolution, I was able to separate the radio emission from the formation of stars and the radio emission associated with the super-massive black holes, for 940 galaxies in one image (previous studies at high frequencies are limited to around 30 galaxies from one image). This has showed that very faint galaxies have a mixture of different kinds of radio emission, and that even in brighter galaxies, there can be significant contributions to the overall radio emission from super-massive black hole activity. This is an important step towards helping achieve the objectives of my fellowship, which aim to understand how super-massive black holes can impact the formation of stars in distant galaxies.
Exploitation Route The outcome of these results will form the basis for further work on the topic of understanding how super-massive black holes can impact the formation of stars in distant galaxies (STFC Science Challenge A). It will be useful in my own work going forward, but also as a general method for others in the astronomical community who are working on this topic.
Sectors Other

URL https://doi.org/10.1093/mnras/stac2129
 
Title LOFAR VLBI common workflow language pipeline 
Description The Low-Frequency Array Very Long Baseline Interferometry (LOFAR-VLBI) pipeline is a calibration and imaging pipeline that includes all of LOFAR's international stations. It looks and solves for delays using an in-field calibrator within the field of view of the pointing. The pipeline provides: solution tables written in a file in the hierarchical data format (version 5), referred to as an h5parm, a self-calibrated, corrected dataset for the in-field calibrator. The delay solutions are applied back to the original data. From there the pipeline can split out smaller datasets in the desired target direction(s) within the field of view. 
Type Of Technology Software 
Year Produced 2023 
Open Source License? Yes  
Impact This is the first working version of the LOFAR-VLBI pipeline in the common workflow language. As a community, LOFAR is moving towards common workflow language for all of its data reduction. This pipeline, although only recently published, can be seamlessly integrated into our production workflows for processing LOFAR-VLBI data. 
URL https://zenodo.org/record/7737402
 
Title LOFAR-VLBI pipeline v4.0.0 
Description This is a new release of the pipeline which processes LOFAR data at high resolution. The pipeline now uses a more robust self-calibration algorithm, which improves the results. 
Type Of Technology Software 
Year Produced 2022 
Open Source License? Yes  
Impact None yet. 
URL https://www.aanda.org/articles/aa/pdf/2022/02/aa40649-21.pdf
 
Title lmorabit/ILT_AGNdetect: Initial release 
Description First release of this public code. 
Type Of Technology Software 
Year Produced 2023 
Open Source License? Yes  
Impact Public software used for data reduction in publication with DOI: 10.1093/mnras/stac2129 
URL https://zenodo.org/record/7625659
 
Description Durham Celebrate Science 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Durham Celebrate Science is a 3 day event where various science departments from Durham University set up a series of activities and experiments for members of the local and regional public to participate in. For astronomy, 19 members volunteered to be stationed at 1 of 4 astronomy activities for a 3 hour session. These activities included the Universe Creator, a gravitational lensing simulation, and 2 virtual reality headsets walking through the Eagle simulations. Each day saw approximately 2000 visitors of all ages and was documented by local media.
Year(s) Of Engagement Activity 2022
URL https://www.durham.ac.uk/news-events/events/events-archive/2022/celebrate-science-2022/
 
Description Durham Girls' Astronomy Day 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact 45 pupils from local schools attended for a school visit to the research organisation, many of whom are from underpriviledged socio-economic backgrounds. The event was aimed towards school girls, as women are underrepresented in Physics. The girls interacted with researchers throughout the day, asking questions and having discussions about research and what it's like to work at a university. The schools reported increased engagement from the pupils in all subjects after the event, with a specific interest in STEM topics.
Year(s) Of Engagement Activity 2023
URL https://durham-astro-girlsday.com/
 
Description Interview for national news 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact The BBC picked up a press release on the work my award focuses on, and I was interviewed for BBC evening news. The interview was also picked up and reported by BBC World news. I also conducted 14 morning breakfast radio interviews the following day, for regional audiences all across the UK, and the research / press release was covered in a YouTube video on a science channel run by an astronomer, with more than 300,000 subscribers. There were over 50 pieces of national / international media on this.
Outcomes:
- requests to give lectures on my research, for amateur astronomy societies and other organizations
- increased interest from undergraduate students who would like to work on my team
Year(s) Of Engagement Activity 2021
URL https://www.bbc.co.uk/news/science-environment-57998940
 
Description Lectures for amateur astronomical societies / special interest groups 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact The intended purpose of these talks was to provide an overview of the research carried out by myself and my team, for the general public.
I gave talks to 3 amateur astronomy societies, and one rotary club.
The feedback I received was that these talks had increased interest in some of the younger members. I also received follow up questions indicating increased interest in the topic.
Year(s) Of Engagement Activity 2021,2022
 
Description School Visit - Ferryhill School 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact On 27 April 2022, 5 members of the department attended Ferryhill School to interact and teach year 9 students about astronomy. The activity was split into 4 session where presentations were given about astronomy, how to become an astronomer, and what it is like being an astronomer. Each session consisted of 1 year 9 class made up of approximately 40 students. There was lots of interest and questions from students about the universe and various phenomenon with it.
An activity for the students was also provided where they were instructed to create a universe using Galaxy Makers - an online program developed at the Institute for Computational Cosmology at Durham University. After students would create their own universe, they were met with a list of statistics illustrating how close they were to creating a universe similar to our own. The student took particular interest in trying to get as close to the real universe as possible by asking many questions and making use of the information presented at the start of the session.
We had received feedback from the school indicating that the visit was well received and that students had thoroughly enjoyed the session.
Year(s) Of Engagement Activity 2022