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Black holes and their host galaxies: coevolution across cosmic time

Periodic Reporting for period 4 - COEVOLUTION (Black holes and their host galaxies: coevolution across cosmic time)

Reporting period: 2020-03-01 to 2021-08-31

Galaxy formation is one of the most fascinating yet challenging fields of astrophysics. The desire to understand galaxy formation has led to the design of ever more sophisticated telescopes which show a bewildering variety of galaxies in the Universe. However, the degree to which an interpretation of this wealth of data can succeed depends critically on having accurate and realistic theoretical models of galaxy formation. While cosmological simulations of galaxy formation provide the most powerful technique for calculating the non-linear evolution of cosmic structures, the enormous dynamic range and poorly understood baryonic physics are main uncertainties of present simulations. This impacts on their predictive power and is the major obstacle to our understanding of observational data. The objective of this proposal is to drastically improve upon the current state-of-the-art by i) including more realistic physical processes, such as those occurring at the sphere of influence of a galaxy’s central black hole and ii) greatly extending spatial dynamical range with the aid of a novel technique I have developed. With this technique I want to address one of the major unsolved issues of galaxy formation: “How do galaxies and their central black holes coevolve?” Specifically, I want to focus on three crucial areas of galaxy formation: a) How and where the very first black holes form, what are their observational signatures, and when is the coevolution with host galaxies established? b) Is black hole heating solely responsible for the morphological transformation and quenching of massive galaxies, or are other processes important as well? c) What is the impact of supermassive black holes on galaxy clusters and can we calibrate baryonic physics in clusters to use them as high precision cosmological probes?
During the ERC grant all proposed objectives have been studied in detail and significant scientific progress has been made in addressing the key scientific questions posed above in agreement with or exceeding the proposed work plan.
Overall the progress of the ERC project has been excellent. The COEVOLUTION team had the necessary expertise in all areas of the ERC grant and it collaborated with a number of PhD students (~10), master students (~5) and a number of external collaborators. The team was very productive with 48 publications so far in high impact journals and was very active in disseminating scientific results, attending or organizing over 80 international conferences. The team was heavily involved in organizing a local scientific workshop which brought international experts to the team's host institution as well as co-organizing a Special Session at EWASS in 2018. In 2019 PI organized a major international symposium whose summary was covered in the Nature journal. The team has been very successful in winning high performance computing grants. The team was heavily engaged with public outreach as well, reaching over 1200 people a year during the Cambridge Science Festival.

In terms of the key scientific achievements, here is a summary of a few highlights.

Colin DeGraf has mainly worked on Area A of the ERC grant. He has developed novel black hole seed models and demonstrated their impact in state-of-the-art simulations. This is very relevant for the cosmic black hole merger rates that future gravitational wave detectors will be able to probe (IPTA, LISA), and this work allowed us to join the LISA consortium. This work is summarized in DeGraf & Sijacki, 2020, MNRAS, 491, 49. More recently, Colin also worked on the emerging field of multi-messenger astrophysics, demonstrating the link between merging black holes and morphological signatures of their host galaxies, with key results summarized in DeGraf et al., 2021, MNRAS, 503, 3629. Colin DeGraf has also worked on Area B of the ERC grant, exploring the co-evolution of black holes and galaxies. This resulted in two published papers.

Martin Bourne has mainly worked on Area C of the ERC grant. He has developed an entirely novel method of black hole heating via jets based on the work by Curtis & Sijacki, 2015, MNRAS, 454, 3445. Given the timeliness he has applied this method to compare against the Hitomi (former Astro-H) mission and to constrain the properties of galaxy clusters, heating and turbulence. This work has been published in Bourne & Sijacki, 2017, MNRAS, 472, 4707, Bourne, Sijacki & Puchwein, 2019, MNRAS, 490, 3 and Bourne & Sijacki, 2021, MNRAS, 506, 4 and resulted in Royal Astronomical Society Press Release.

Martin Bourne has done further work related to Area B of the ERC grant exploring the interplay between star formation in galaxies and AGN feedback. This resulted in 4 published papers where specifically emphasis has been placed on the nature of AGN outflows. This together with our efforts with external collaborators (Costa et al. 2018, MNRAS, 473, 4197) has put us in the leading position of theoretically interpreting observational data and currently there is an ongoing fruitful collaboration there. Further more, together with our PhD students Sophie Koudmani and Rosie Talbot, Martin has worked on a novel field of AGN feedback in dwarf galaxies and on the first ever implementation of Blandford-Znajek jets in galaxy formation simulations which resulted in 3 published paper and one submitted.

Davide Fiacconi has developed a novel method to incorporate the effect of black hole spin and its imprint on black hole accretion and feedback. This model is needed for diverse parts of Area A, B and C. The model is fully functional now and a paper has been published (Fiacconi, Sijacki, Pringle, 2018, MNRAS, 477, 3807). Note that this model is especially timely given the recent detection of gravitational waves, as it will also permit to simulate merging black holes with a spin. Davide also worked on the evolution of galaxies in the early Universe and on the nature of X-ray sources pertinent to Area B of the ERC grant which resulted in 2 published papers.
The COEVOLUTION team has developed completely new numerical techniques to study the evolution of galaxies and their central black holes which are at the forefront of the field. The team has proven in a number of publications that these techniques are not only innovative and more accurate than previous methods, but that they change the physical understanding of galaxy formation in several important ways. The team has applied these techniques on a broad range of topics, which permitted to shed new light on the formation and evolution of galaxies and black holes. This has produced a significant impact in the scientific community mirrored in a large number of conference talks that our team members have given. The team has additionally produced a more broader socio-economic impact by actively participating in the University of Cambridge Science Festival from 2015-2019 (which was suspended in 2020 and 2021 due to the pandemic). More than 1200 visitors (each year) came to our institute where the team members have engaged with the public (including many children) explaining in layman terms the science supported by this ERC grant. This has been accomplished through posters, video displays, interactive computer simulations as well as hands on experiments for all ages. Finally, the team PI has been awarded the 2019 PRACE Ada Lovelace Award for high performance computing (HPC) for her outstanding contributions to and impact on HPC in Europe.
A galaxy in the early Universe with the central black hole simulated by the COEVOLUTION team