Using Cosmic Beasts to Uncover the Nature of Dark Matter

Lead Research Organisation: Durham University
Department Name: Physics

Abstract

The nature of dark matter is the most elusive question in modern physics. Only 5% of the Universe by weight consists of standard model particles. The remaining 95% would be composed of 'Dark Matter' and 'Dark Energy'. These are invisible, and most particle physics theories predict dark matter to interact so weakly with standard model particles that it will remain fundamentally undetectable in terrestrial experiments. If these theories are correct, dark matter can only be studied where it gathers in sufficient quantities for its gravity to affect things around it we can see. I propose to track the behaviour of dark matter in galaxy clusters (the most massive structures in the universe, also called 'cosmic beasts'), to distinguish between the 3 leading models: cold, warm and self-interacting dark matter.

My proposal exploits a dramatic recent increase in observations of galaxy clusters by the world's biggest telescopes, reflecting the field's recognition as a top priority goal. I have been awarded observing time on the Hubble Space Telescope in the largest category of programme (>100 orbits) to obtain the deepest ever imaging of clusters' surroundings, plus follow-up spectroscopy from the largest telescope on Earth (VLT). I designed these observations to map clusters' dark matter, via the effect of 'gravitational lensing', which distorts and magnifies objects behind the cluster. I will use these data (i) by themselves, (ii) to calibrate the largest (but shallow) Hubble imaging awarded to the host institute (iii) to set the agenda for, and optimise facilities like Euclid, Athena and the James Webb Space Telescope through the 2020s.

Cosmological simulations indicate that galaxy clusters are the best laboratories to distinguish between models of dark matter, because they are still growing. Clusters grow by merging with each other; every merger acts like a gigantic particle collider. The properties of dark matter are revealed by its trajectory through a collision, which should be between that of stars and of (hydrogen) gas. The properties of stars and hydrogen are well understood, so they bookend measurements of dark matter like the calibration points on a thermometer at 0C and 100C.

Traditional research programmes usually separate measurements of dark matter, stars and gas, because they require observations from different (infrared, ultraviolet, X-ray) telescopes. I have developed a multiwavelength analysis, to enable previously impossible measurements such as the time-scale on which dark matter and gas is funneled into clusters, how quickly clusters reach equilibrium, and constraints on possible dark matter particle interactions.

I have also led the establishment of a new research area, which I will expand during the FLF. When transient events (such as supernova explosions) happen behind a galaxy cluster, light from the explosion can be gravitationally lensed and visible along more than one line of sight. Measuring the time delay between multiply-imaged versions of a supernova increases the resolution with which the cluster's dark matter can be mapped. Furthermore, predicting the time delay is one of those rare, precious occasions in astrophysics where a hypothesis can be subjected to a true Popperian test, within the timescale of a few years. I have intentionally scheduled my HST and VLT observations to enable the discovery and monitoring of transient events. They also offer the (high risk/high reward) possibility of discovering electromagnetic counterparts to lensed gravitational wave events.

My UKRI FLF research programme will thus exploit the latest multiwavelength data from world-class facilities. It uses my high-precision techniques to analyse big data, and will be interpreted within the world-leading theoretical framework of Durham's state-of-the-art cosmological simulations.

Planned Impact

My UKRI FLF research project does not directly have a significant impact on the private sector, but its impact on the public sector can be large. I propose to hold my fellowship at Durham University in the North-East of England. This region has the lowest participation rate in higher education in the UK, making public engagement here a priority!

The visual nature of astronomy makes it accessible to a large audience. Research into dark matter receives particularly broad coverage in international media (I have run 5 press releases through NASA/ESA/ESO in the past 5 years, and my FLF proposal has even stronger media potential). Nevertheless, astronomy provides direct exposure to the cut-and-thrust of the scientific method, in complex areas of fundamental physics. For example, my project will measure dark matter by the way it warps space and time - a consequence of General Relativity first predicted by Albert Einstein. Members of the public are often amazed and intrigued that light does not always travel in straight lines, when space itself is curved. Photographs that I have taken through telescopes demonstrate this effect, in a visceral introduction to the weird world of modern physics.

I will exploit the opportunity that the fellowship provides for job security in one place, to expand my network of contacts and volunteering commitments with schools and in public events. I have a particular interest in making science appealing to young people, especially girls, and have given public talks and recruited students with an emphasis on making science a female-friendly environment. For example, I animated planetarium shows at the 2016 Celebrate Science Festival in Durham, which attracted over 7000 visitors as part of a drive to increase participation with and applications to the university from locals.

My area of research is growing rapidly, and I also propose to mentor students in the field through undergraduate and postgraduate degrees. Much of this growth is driven by the ESA Euclid satellite, scheduled for launch in 2022 and now involving a consortium of >1000 scientists across Europe. I am highly involved into two committees for the Euclid science consortium, aiding both Early Career Researchers, and championing Equality and Diversity Issues. In case the intrinsic excitement of discovering the nature of the most common materials in the universe were not obvious, I have also developed and delivered one short course of lectures to 3rd year physics undergraduates, and another course to first year PhD students. I have supervised 1 PhD and 4 MSc students to completion, all four of whom decided to continue in academia and successfully secured positions in the next stage of their academic career. I also recruited, raised funding for, and am now de facto lead supervisor for another PhD student, currently in her second year.

A great deal remains to be done to make scientific research and STEM more attractive and generally equitable. I intend to contribute as much as I can to that effort, using my dynamism and the opportunities offered by both the FLF and the outreach group at the host institute.

Publications

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Deason Alis J. (2021) Stellar splashback: the edge of the intracluster light in Monthly Notices of the Royal Astronomical Society

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Gill Ajay (2020) Optical Night Sky Brightness Measurements from the Stratosphere in The Astronomical Journal

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Harvey David (2021) Reconciling galaxy cluster shapes, measured by theorists versus observers in Monthly Notices of the Royal Astronomical Society

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Jauzac M (2019) The core of the massive cluster merger MACS J0417.5-1154 as seen by VLT/MUSE in Monthly Notices of the Royal Astronomical Society

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Jauzac Mathilde (2019) The core of the massive cluster merger MACS J0417.5-1154 as seen by VLT/MUSE in Monthly Notices of the Royal Astronomical Society

 
Description Since my award I was contacted to become the Scientific Advisor for the IAU-NOC Mauritius Committee. We dealt witht he Exoworld Campaign last year, offerign the possibility to Mauritians to name a star and its exoplanet. 2020 will be devoted to the Blue Dot Campaign.
First Year Of Impact 2019
Sector Education,Leisure Activities, including Sports, Recreation and Tourism,Culture, Heritage, Museums and Collections
Impact Types Cultural,Societal

 
Description co-Chair of the Euclid Consortium Diversity Committee (ECDC) 
Organisation Paris Institute of Astrophysics
Country France 
Sector Academic/University 
PI Contribution I have been a member of the ECDC for nearly 3 years, but was nominated co-Chair of the Committee early January 2020. We are in charge of ensuring Diversity, Equality and Inclusion are respected in the Consoritum .Euclid is the next ESA space telescope, scheduled to be launched in 2022, and includes >1500 members between Europe and the US. As co-Chair, I am directly in contact with the EC Board, and assist the Chair in solving issues (formal and informal complaints) and presenting new ideas to the Board (as an exampe, I presented the idea of a formal trainign for all leads of working groups).
Collaborator Contribution The IAP is hosting the PI of Euclid. Euclid includes so many institutes that I cannot list them all.
Impact Most of th eoutcoems from the ECDC are ocnfidential.
Start Year 2020
 
Title hybrid-Lenstool 
Description hybrid-Lenstool is a new lensing mass modeling software, built on the intiial Lenstool software which have bene used by my collaborators and I since the end of the 90s. hbrid-Lenstool now implements the joint optimization of strong and weak lensing constraints, combining parametric and nonparametric modeling, in order to map the mass distribution in clusters. This ismandatory in order to get the most precise and accurate mass models. 
Type Of Technology Software 
Year Produced 2020 
Open Source License? Yes  
Impact Mass models for all BUFFALO clusters under preparation, with the highest precision and accuracy reachable today. hybrid-Lensotol will be made publicly available within the enxt 6 months. 
URL https://arxiv.org/pdf/2002.04635.pdf
 
Title pyRRG 
Description pyRRG is shape measurement software. It measures the shapes of galaxies, while correcting them from PSF. pyRRG is semi-automatic and is the main shape measurement software used in BUFFALO for our weak-lensing analyses. It includes the deteciton of sources, the star/galaxy classifciation, shape measurements, and identification of foreground contaminants. 
Type Of Technology Software 
Year Produced 2019 
Open Source License? Yes  
Impact It allows the semi-automatic measurements of galaxy shapes, mendatory step in the ocnstruction of weak-lensing catalogues. As it is used now in BUFFALo, all future publications regarding weak-lensing analyes will use it. At the moment we have 4 publication in preparation which use pyRRG. 
URL https://arxiv.org/pdf/1911.06333.pdf
 
Description DEX XVI - 2020 vision: progress and tensions in astronomy 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Other audiences
Results and Impact I organized the DEX XVI meeting here in Durham. This year we historically reached more than 100 participants. It is a unique meeting which favours interactions between students, postdocs and staff holed over 2 days.
Year(s) Of Engagement Activity 2020
URL http://astro.dur.ac.uk/DEX/XVI/
 
Description EAS 2020 Symposium : Panchromatic and hyper-spectral observations of cluster Lenses and lensed galaxies 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact I was awarded a 2 days slot to organize a Symposium at the European Astronomical Society Annual Meeting, happening June 29-July 3 in Leiden (Netherlands).

https://eas.unige.ch//EAS_meeting/session.jsp?id=S4
Year(s) Of Engagement Activity 2020
 
Description School visits in Mauritius 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Schools
Results and Impact i visited a school in Mauritius for 3 days back in 2019 to present Astornomy and Astrophysics to 9 classes (6-11 years old kids).
Year(s) Of Engagement Activity 2019
 
Description Scientific Advisor for the IAU-NOC Mauritius Committee 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact As a scientific advisor for the IAU-NOC Mauritius Committee, I am incharge of checking all announcements made. The IAU-NOC Mauritius Committee is in charge of implementing IAU Astronomy outreach initiatives in Mauritius.
Year(s) Of Engagement Activity 2019,2020
URL https://iau-noc-mur.netlify.com/