2021 Seminar Abstracts

Clive Tadhunter

Title: How are quasars triggered?

Discovered more than 50 years ago, quasars are the most luminous objects in the Universe and are thought to play
a key role in the evolution of galaxies. However, despite their importance, we still do not fully understand how they are triggered.
Following a review of the quasar triggering problem and past results in this field, I will present new results based on deep optical
imaging and far-IR photometry of nearby quasar-like AGN, emphasising in particular recent Herschel results.

Natasha Jeffrey

Title: Solar flares: our laboratory for understanding particle acceleration and transport processes

Solar flares are efficient particle accelerators and prime laboratories for studying astrophysical acceleration processes, with a high fraction of the released magnetic energy being carried by energetic particles. Over the last decade, our understanding of particle acceleration and transport in flares has been enhanced by new models and available multi-wavelength observations from X-rays to (E)UV to radio. However, many questions remain about how and where energetic particles are accelerated, and how different plasma environments (e.g., collisions, turbulence) affect the transport and observed properties of energetic particles. In this talk, I will review some of these advances and also discuss upcoming X-ray stereoscopic observations with Solar Orbiter/STIX and new X-ray missions at Earth.

Stephen Hodge

Title: G-SCALE: Accelerating the Commercialisation of Graphene

Versarien plc is an advanced engineering materials group. Leveraging proprietary technology, the group creates innovative engineering solutions for its clients in a diverse range of industries. Our UK subsidiaries are leaders in the field of graphene and related layered materials (GRMs) production and commercialisation; 2-dTech Ltd., which specialises in the supply, characterisation and early stage development of graphene products; ACC Cyroma Ltd, which specialises in the supply of vacuum-formed and injection-moulded products to the automotive, construction, utilities and retail industry sectors; and Cambridge Graphene Ltd. supplies novel inks based on graphene and related materials to develop graphene materials technology for licensing to manufacturers.

This talk will outline our ambitious GSCALE programme to accelerate the scale-up of 5 manufacturing approaches; and will create shop floor QC processes to facilitate the efficient delivery of required volume production of graphene powders, dispersions, compounds and masterbatches. Our approach is to move “SCALE” products to TRL8/9 through testing, validation and technical improvements to achieve required standards in volume opportunities.

John Armstrong

Title: A Machine Learning Approach to Correcting Atmospheric Seeing in Solar Flare Observations

Current post-processing techniques for the correction of atmospheric seeing in solar observations – such as Speckle interferometry and Phase Diversity methods – have limitations when it comes to their reconstructive capabilities of solar flare observations. This, combined with the sporadic nature of flares meaning observers cannot wait until seeing conditions are optimal before taking measurements, means that many ground-based solar flare observations are marred with bad seeing. To combat this, we propose a method for dedicated flare seeing correction based on training a deep neural network to learn to correct artificial seeing from flare observations taken during good seeing conditions. This model uses transfer learning, a novel technique in solar physics, to help learn these corrections. Transfer learning is when another network already trained on similar data is used to influence the learning of the new network. Once trained, the model has been applied to two flare data sets: one from AR12157 on 2014 September 6 and one from AR12673 on 2017 September 6. The results show good corrections to images with bad seeing with a relative error assigned to the estimate based on the performance of the model. Further discussion takes place of improvements to the robustness of the error on these estimates.

James Trussler

Title: Unveiling the roles of mass, environment and structure in galaxy quenching

Star-forming galaxies can be transformed into passive systems by a multitude of processes that shut down (i.e. `quench’) star formation, such as the halting of cold gas accretion (`starvation’) or the rapid removal of gas in AGN-driven outflows. However, it remains unclear which processes are the most significant, primary drivers of the star-forming—passive bimodality.

In this talk, I will discuss how measurements of the relative level of chemical enrichment in star-forming and passive galaxies can be used to derive valuable new insights into the quenching process. Leveraging on the statistical power of the Sloan Digital Sky Survey—the largest spectroscopic galaxy survey in the local Universe—I will discuss how galaxy quenching depends on the internal properties of galaxies (stellar mass), external factors (environment), and how it varies radially within galaxies.

I will show that the significant difference in stellar metallicity between star-forming and passive galaxies implies that starvation is primarily responsible for quenching star formation in galaxies of all masses. Additionally, I will discuss the weak imprint of environment on the stellar populations of galaxies, and how this indicates that environmental effects only contribute moderately to the starvation of low-mass satellite galaxies in dense environments. Finally, using spatially-resolved spectroscopy from the MaNGA galaxy survey, I will highlight how the relative roles of different quenching mechanisms vary with radial distance in galaxies.

Paul Warren

Title: Energy Efficiency and Energy Production – How R&D in the Flat Glass Industry is Making a Difference

With climate change dominating the headlines, the subjects of energy efficiency and low-carbon energy production are becoming more and more important. The flat glass industry can make a significant contribution in both these areas – specifically via the use of large-area glass surfaces coated with transparent, conducting coatings. In this presentation, I will outline the basic science involved in these technologies and explain how R&D is leading to improved product performance in both areas.

Aleksandra Leśniewska

Title: Dust production and dust destruction in galaxies

Dust production is a very important issue in galaxy evolution. Unfortunately, we are still unable to determine its formation mechanism. I will present the investigation of dust production in nine galaxies at redshift z > 6, for which dust emission has been detected. In recent years, more accurate measurements were made using the most powerful instruments, eg ALMA, which contributed to better estimates of luminosities and sizes, and thus to determine the masses of gas, dust and stars in the studied galaxies. We conclude that asymptotic giant branch (AGB) stars did not contribute to the dust formation significantly in these Early Universe galaxies, and that supernovae are unlikely to produce the bulk of the dust mass.

The mechanism of dust removal from galaxies has not been completely understood yet. However, dust evolution is not only relevant in the context of interstellar medium, but is also one of the main factors defining the evolution of stars and the entire host galaxy. In my project I will address this issue by the analysis of several thousand dusty galaxies, which are becoming passive, investigate the relationships between properties to understand the dust removal. The analysis will be conducted on a sample that differs from previous work not only in the number of objects, but most of all in a wider range of parameters.

Ben Williams

Title: From Lab. To Fab: How fundamental materials science is used to progress Oxford PV’s perovskite/Si PV technology

At the forefront of an exciting period in commercial PV, Oxford PV is developing and producing a new technology that will significantly increase the energy density of commercial photovoltaics. Our tandem perovskite/Si technology uses existing production routes, whilst drastically enhancing the power output with the addition of low-cost perovskite top-cell processes. Supported by excellent advancements in the field of perovskite photovoltaics in recent years, we have demonstrated a world-record efficiency of 29.5%, which far exceeds the record Si single junction performance (26.7%) and even exceeds the physical limit of Si-PV (29.3%). We will commence production at our fully integrated line at our German site early in 2022.

In this talk I will discuss a number of aspects of the work carried at our R&D site in Oxford, where we are continually developing the perovskite technology aiming to further enhance the ceiling performance. We take a multidisciplinary approach, utilising our physics and chemistry experts across the field of materials science. Technical challenges are addressed from a fundamental perspective, often using semiconductor physics models to design device configurations, and advanced electrical characterisation to understand efficiency losses and identify routes to higher efficiency, ensuring that processing routes are viable to be transferred to an industrial environment. In order to assess the robustness of these routes, we have also installed a methodology to be able to track the material properties at each stage of cell development to be able to identify critical parameters and/or contributors to weaknesses in cell design or process selection. To finalise, I will provide a brief look at activities happening at our industrial site.

Stephen Eales

Title: Dust in the Universe from z=0 to z=5

The cool reservoirs of molecular hydrogen in galaxies cannot be detected directly, and so astronomers have only be able to investigate these reservoirs indirectly using tracers such as CO molecules and more recently dust grains. These tracers are only useful if we know the ratio between the tracer species and molecular hydrogen. In the first part of this seminar I show that observations of nearby galaxies show that the properties of dust vary both within galaxies and between galaxies. I describe the first results from a submm survey of the Andromeda galaxy, one of whose aims is to uncover the physical and chemical reasons for this variation. In the second part of the seminar, I show some results from ALMA observations of the gravitationally-lensed ‘Rosetta Stone’ galaxy that show the ratios of tracer species to molecular hydrogen can be many times higher at high redshift than it is in the universe today.

Ruizhi Yang

Title: LHAASO and the Galactic Cosmic rays

Cosmic rays (CRs) is one of the most important component in the interstellar medium (ISM) in our Galaxy. However, the diffusion of CRs in turbulent magnetic fields erases the information on the distribution of CR accelerators to a large extent, and the energy dependent diffusion of CRs also significantly modifies the initial (acceleration) spectra of CRs. In this regard, gamma-rays, the secondary products of interactions of CRs with gas and photons in the interstellar medium (ISM), provide us more information about the origin of CRs. The Large High Altitude Air Shower Observatory (LHAASO) is the gamma-ray and cosmic ray detector observatory in Sichuan province, China. With the unprecedented sensitivity of gamma-rays above 10 TeV, LHAASO would be the ideal instrument to perform such kind of study. In this talk I will introduce the current status and prospect of LHAASO observations and the implications on CR related science.

Larry Widrow

Title: In the Balance: Statis is Disequilibrium in the Milky Way

The disk of the Milky Way comprises some 100 billion stars on nearly circular orbits about the Galactic centre. Within a few years, the Gaia Space Telescope will measure positions and velocities for over 1% of these stars. By combining equilibrium models of the Galaxy with these observations we can construct the Galactic rotation curve, which allows us to infer the large-scale structure of the dark matter halo. We can also construct a model for the mass distribution in the Solar Neighbourhood, which allows us to infer the local density of dark matter. However, even a cursory study of the Milky Way reveals structures that signal a departure from equilibrium. The most prominent of these are the Galactic bar, spiral arms, and warping of the outer disk. I will describe recent observations of some more subtle departures from equilibrium and discuss ways in which these observations can lead to refined models of the Galaxy and a more complete picture of the Galaxy’s dynamics.

Edward Laird

Title: Searching for dark matter using quantum technology

Dark matter makes up 84% of our galaxy, but despite extensive searches its composition is unknown. One compelling idea is that it consists of axions. These are hypothetical particles which have been proposed as an addition to the standard model to explain why the strong nuclear force obeys CP symmetry. In this hypothesis, every galaxy is surrounded by a halo of axions, created shortly after the Big Bang but barely interacting with ordinary matter ever since. Detection of dark matter axions would therefore simultaneously solve two of the greatest mysteries of 21st century physics.

Axion theory predicts a very clear signature of their existence: When axions from the galactic halo pass through a magnetic field, some of them will decay into photons, whose frequency is determined by the axion mass. However, the expected electrical signal is tiny, meaning that an axion search experiment must scan slowly through the range of possible masses. Only a small part of the available range has so far been searched.

One way to dramatically speed up the search rate is to detect the electrical signal using quantum amplifiers. Instead of using semiconductor transistors, like most electrical amplifiers, quantum amplifiers are based on Josephson junctions between superconductors. They can even be operated in a way that circumvents the standard quantum limit, which is a consequence of the uncertainty principle, by using the advanced measurement technique of quantum squeezing. This capability could make it possible to search the axion parameter space much faster that previously.

As part of the UK Quantum Technology Programme, we have recently established a consortium to take advantage of these developments and carry out a world-leading axion search in the UK. I will describe how this marriage of particle physics with condensed-matter quantum technology aims to search for axions – or perhaps even to discover them.

Manolis Xilouris

Title: How many old and young stars do local galaxies host?

Many simple questions in astronomy remain vastly unexplored. One such question concerns the stellar populations in galaxies of different morphologies in the local universe. In its simplest form, one might ask “how many old and young stars do local galaxies host?”. Using the observations from the “DustPedia” database (http://dustpedia.astro.noa.gr) the Spectral Energy Distributions (SEDs) of ~800 local galaxies were modeled and the properties of cosmic dust and its interaction with the stellar radiation were investigated in a systematic way. In a similar way, the properties of local (Ultra-) Luminous Infrared Galaxies, with data from the “GOALS” database (https://goals.ipac.caltech.edu) were investigated. In my talk I will present the results of these recent studies.