Two projects on black hole accretion and jet formation as part of a large European team
Black holes are the sites of the most extreme physics in the universe since the Big Bang. Their most poorly understood characteristic is the formation of powerful collimated outflows of mass and energy, moving at extremely high speeds away from the region of the event horizon. These ‘relativistic jets’ can have a huge impact on their surrounding environments, even regulating the growth of the most massive galaxies on cosmic scales.
Black holes also span an enormous range in masses and hence timescales. In the lowest mass black holes, stellar-mass black holes in ‘X-ray binary’ systems, we can track the jets from their formation and launch at just a handful of event horizon radii to their eventual deceleration and termination in the interstellar medium a year or so later. Our team in Oxford leads the world in studying the connection between these jets and the inner accretion flow, as well as their late-time deceleration phases, where they finally dissipate their launch energy in the ambient interstellar medium. We lead major guaranteed-time radio observing programmes of black holes on a number of radio telescope arrays, including MeerKAT in South Africa, as well as working at the interface between observation, interpretation and numerical modelling.
We have two DPhil positions available to work on aspects of black hole accretion and jet formation. These projects are funded as part of a large European project, Blackholistic, a partnership between The University of Oxford, The University of Amsterdam and Radboud University. The project is affiliated to the large Event Horizon Telescope collaboration. As a result we encourage applications from candidates who are keen to work in a large and dynamic international team, and who are enthusiastic to work both with data and their interpretation.
Project 1: Relativistic jets from black holes from birth to termination
Supervisors: Rob Fender and Ian Heywood
In this project we will complete our understanding of the entire life cycle of these jets, using very long baseline interferometry (VLBI) to image relativistic jets from stellar mass black holes within minutes of their launch. These will be synchronised to later observations on larger scales with radio arrays such as MeerKAT to provide comprehensive monitoring from launch to termination. We will push on the existing state of the art by going to high frequencies, and coordinating with multiple facilities at other wavelengths. In the second half of the project we will explore how the Event Horizon Telescope can be used in a rapid-response mode to directly resolve these dynamically evolving jets closer to the black hole than ever previously possible.
Project 2: Scaling black hole accretion and jet formation from stellar-mass to supermassive black holes
Supervisors: Rob Fender and James Matthews
In this project we aim to understand how we can test models of jet formation in the accretion flow and how these processes scale across the black hole mass range from stellar-mass to supermassive black holes. In particular we will work with teams in The Netherlands to see what observational tests can be made of their general relativistic MHD jet launch modelling, will work on propagating jets from launch to termination in our own relativistic HD simulations, and will test - via a combination of observational interpretation and modelling - how these processes scale with mass and the properties of the ambient environment. This problem is inherently multi-scale and will connect the small scale black hole and accretion physics with the large scale dynamics of astrophysical jets, touching on accretion, jet formation, particle acceleration and shocks. The successful applicant will be prepared to work at the interface of observation, theory and modelling, and will be comfortable working in a large international collaboration.
The formation and cosmic evolution of relic galaxies
Supervisors: Chiara Spiniello, Michele Cappellari
The most massive and oldest galaxies in the Universe (early-type galaxies, ETGs) play a fundamental role in the process of structure formation, as they account for more than half of the total mass in the Universe. However, the details of their formation and evolution is a contentious question in present-day extragalactic astrophysics and cosmology. Recently, a “two phase formation scenario” (Fig.1) has been proposed. According to this scenario, massive ETGs formed the bulk of their stars only a few billion years after the Big Bang, via a very quick and violent star formation episode. Then, during a second, more time-extended phase, they merge with other galaxies or gas falls into them and forms new stars. This causes a dramatic growth in size and transforms them into the massive, giant elliptical galaxies we observe today. Unfortunately, in local giant galaxies, this secondary "accreted" material contaminates the "pristine" component that encodes the information about the first phases of assembly. This irremediably masks the very early stages of galaxy formation in the Universe. Relic galaxies have instead continued on their isolated life without increasing their size or, importantly, without changing their stellar content since their formation. Studying them is akin to an archaeologist learning from dinosaur fossils. They have the potential to unlock our understanding of the very early formation of galaxies within our Universe. But how many relics exist at each cosmic epoch in the Universe? How could they passively evolve through cosmic time without experiencing any interaction with other systems? And in which kind of environment are they preferentially found? Answering to these questions constitute the core of this PhD project. The student will work within the INvestigating Stellar Population In RElics (INSPIRE) project, analysing spectroscopic data of a sample of relic candidates at different cosmic distances, characterising their stellar population, mass structure, kinematics and dynamics, and comparing them with a control sample of normal-sized galaxies of similar stellar mass. Combining this info with hydrodynamical simulations they will seek to understand how the densest and most compact objects in the Universe formed and how they evolved into local ellipticals. INSPIRE website: https://sites.google.com/inaf.it/chiara-spiniello/inspire
Anomaly Detection with the Vera Rubin Observatory
Supervisors: Chris Lintott, Steve Croft
The large, wide-field, multipurpose LSST survey conducted with the Vera C. Rubin Observatory will bring unprecedented opportunities for scientific discovery. A census of the solar system will result in the discovery of millions of new small bodies, the transient survey will find thousands of new supernovae and other transients each year and deep images will show the low surface brightness universe for the first time. In each of these domains, there exists the opportunity for finding the truly unexpected and unusual.
Such anomaly detection requires the development of new machine learning methods capable of highlighting objects or events worthy of attention. Amongst the data, there exists the possibility of technosignatures - evidence of intelligent life in the Universe - which is a particular focus for this work.
This DPhil, which overlaps with the first data releases from the survey, will develop such techniques for a broad set of science cases. With the opportunity to follow up objects of interest via facilities around the world, this project would suit a student with a broad interest in observational astronomy and a desire to develop skills in citizen science, machine learning and beyond.
Black Holes, Bars and Molecules: A Recipe for Making Bulges
Supervisor: Martin Bureau
This project aims to decipher the intricate structure of bulges, the bright and compact ensembles of billions of stars ruling the centres of galaxies. On the one hand, the masses of supermassive black holes are known to tightly correlate with those of their host bulges, but the causation links, if any, remain unclear. On the other hand, bars are also known to spontaneously buckle and create bulges that are boxy and peanut-shaped. In addition, molecular gas (the fuel for star formation) allows bulges to grow slowly over time. By combining state-of-the-art observations from optical integral-field spectrographs and mm/sub-mm synthesis telescopes, the student will make measurements that directly probe and thus constrain each of these mechanism, thus unraveling the closely intertwined evolution of bulges, disks, and black holes in galaxies.
The student will be part of the GECKOS project (be bold, be different, be GECKOS!), a deep and high-resolution survey of the stars and ionised-gas of 35 nearby edge-on disk galaxies. GECKOS is based on a guaranteed-time large programme utilising the MUSE optical integral-field spectrograph on the Very Large Telescope (VLT), the premier instrument of its kind in the world, but it also includes a number of ancillary surveys (with e.g. ALMA and CFHT/SITELLE). It has a number of complementary scientific aims, and while the student will be expected to focus on the questions above, participating in any and all activities of the team is possible. Extended working visits to Australia, where many team members are based, will be encouraged. The project is particularly suited to a student with an interest in galaxies (structure, dynamics, stellar populations, interstellar medium, evolution) and observational astronomy.
The interplay between environment and galaxy evolution with the new generation of spectroscopic surveys
Supervisors: Matt Jarvis, Catherine Hale & Gavin Dalton
Over the past few decades it has become clear that the environment and dark matter halo mass in which a galaxy resides can strongly influence how it evolves. Thus, in order to understand galaxy evolution we need be able to relate the galaxies to their dark matter haloes and the larger-scale filamentary cosmic web. To do this work, we need accurate positions in 3-dimensional space and the new generation of spectroscopic surveys will provide this information. The student will play a leading role in using these new deep spectroscopic surveys with WEAVE, 4MOST and MOONS to understand how radio sources impact and are impacted by their halo environment, using radio data from LOFAR, MeerKAT and ASKAP. They will have the opportunity to use the best multi-wavelength data to characterise the sources and use the spectroscopic information to perform a 3-D clustering analysis and measure the impact accreting black holes on the process of galaxy formation in dark matter haloes. This project will provide new and important constraints on the feedback process from radio AGN that is used in hydrodynamic simulations of galaxy evolution to truncate star formation in massive galaxies.
The student will also have the opportunity to get involved in other WEAVE-LOFAR and MeerKAT projects and will join a group over 10 postdocs and students all working on galaxy evolution from multi-wavelength survey data. As such the student will become familiar with multi-wavelength survey astronomy and statistical techniques to measure the clustering of different galaxy populations across cosmic time, key skills for exploiting the next generation of surveys from Rubin:LSST, Euclid and the SKA.
Information about WEAVE: https://arxiv.org/pdf/2212.03981.pdf
Information about MOONS: https://arxiv.org/ftp/arxiv/papers/2009/2009.00644.pdf
Information about 4MOST-WAVES/ORCHIDSS: https://www.eso.org/sci/publications/messenger/archive/no.190-mar23/messenger-no190-25-27.pdf
Some background reading on galaxy clustering
Studying the accretion-outflow connection in Active Galactic Nuclei with large observational surveys
Supervisors: James Matthews and Matt Jarvis
Supermassive black holes are thought to lie at the centre of virtually every galaxy, and many of them are "active", in the sense that they accrete matter from their surroundings and give off prodigous amounts of radiation. These Active Galactic Nuclei (AGN) are fascinating and astrophysically important objects. Remarkably, the accretion process also expels outflowing material, a process that can transport huge amounts of energy and momentum to vast distances, allowing the AGN to influence physical proceedings far from its gravitational sphere of influence. These outflows are split into two broad classes -- narrow beams of relativistic material called "jets", and slower, wider-angle flows called "winds". Both winds and jets represent important "feedback" channels, but both are also intimately connected to the underlying AGN accretion disc.
In this project, we will use rest-frame ultraviolet (UV) spectroscopy and radio observations to study the connection between accretion discs and their associated winds and jets in high luminosity AGN (also known as quasars), at moderately high redshift (z~1.5-4). In particular, we will use spectra from the Sloan Digital Sky Survey and WEAVE -- a brand new multi-object spectrograph on the WHT -- to study emission and absorption line signatures of AGN winds. We will combine this analysis with radio data from the LOFAR Two metre sky survey and the MeerKAT SKA pathfinder to look at jet signatures, as well as radio emission from star formation and wind shocks. The overall goal of the project is to build a state-of-the-art census of accretion and outflow activity in AGN and make progress towards a more complete physical understanding of these processes. While the emphasis is primarily observational, the work concerns the extreme physics of black holes, jets and winds, so theory will form an important part of the project; in addition, there will be opportunities to get involved with radiative transfer modelling of the accretion disc and the spectral signatures produced by AGN winds.
The student will join a vibrant research group with the opportunity to work with additional Oxford personnel, in particular research fellow Dr Imogen Whittam, as well as external collaborators in Cambridge, Southampton, Edinburgh, the USA and Chile. Oxford is heavily involved in the LOFAR, MeerKAT and WEAVE projects and the student will have the opportunity to formally join relevant observational collaborations. This will place the student in an excellent position for exploiting other future facilities, such as LSST and the SKA.
Figure: The Carbon IV emission line properties (equivalent width versus blueshift) of a large sample of SDSS quasars, split by powerful radio emission. The radio-loud sources are less likely to have strongly blueshifted line emission associated with winds, suggested an anticorrelation between the two classes of outflows. Reference: Rankine, A.; Matthews, J. et al. 2021, MNRAS, 502, 4154.
Following the threads: Exploration in the data space of the WEAVE surveys
Supervisor: Gavin Dalton
WEAVE is a new spectroscopy facility at the William Herschel Telescope, led from Oxford and now in the commissioning phase. Over the next few years, WEAVE will deliver more than 12,000,000 high quality calibrated spectra for 8 diverse surveys ranging from the structure and evolution of the Milky Way to the formation of the earliest galaxies. Working with the WEAVE PI within a diverse science team spanning 6 countries, this project provides unique access to all aspects of the WEAVE surveys, with possible avenues of exploration including a WEAVE-based calibration of the Hobby-Eberly Telescope Dark Energy Experiment, analyses to search for rare objects within the Milky Way, or spectroscopic identification of gravitationally lensed galaxies.
Simulating galaxies and black holes evolution with Harmoni on the Extremely Large Telescope
Supervisor: Michele Cappellari
Supermassive black holes (BH) are a key element in our understanding of how galaxies form and evolve. However, BH masses have so far only been directly measured for nearby galaxies, where their sphere of influence can be spatially resolved.
The 40m Extremely Large Telescope, which is under construction in Chile, will radically change the situation. Thanks to its large diameter, combined with adaptive optics to correct for the atmospheric blurring, the ELT will allow us for the first time to directly measure BH masses out to most of the history of the Universe.
In this project, the student will use simulated galaxies and dynamical modelling to simulate the measurement of BH masses with the Harmoni integral-field spectrograph from the gas and stellar kinematics of distant galaxies. The student will plan an observing program to trace BH and galaxies evolution across cosmic time with the ELT.
Understanding galaxy quenching from cosmic noon to now: from MaNGA to the JWST
Supervisor: Michele Cappellari
One of the key discoveries of the past decade has been that there is some process that is able to suddenly stop star formation (quench) in galaxies. Without quenching, galaxy models are unable to explain the evolution of galaxies over cosmic time. However, the mechanism for quenching is still debated.
In this project, the student will use observations from the MaNGA spectroscopic surveys of local galaxies and observations of distant galaxies with the JWST, as well as observations at intermediate redshift, to trace the evolution of galaxy star formation history. The student will compare the results derived from observations with numerical simulations of galaxy formation, to try to understand the origin of quenching.
Resolving the crisis of cosmology with gravitational lensing and galaxy dynamics
Supervisors: Michele Cappellari
Are you looking for a DPhil project that will challenge you and help you solve one of the biggest mysteries in cosmology?
The project is part of the TDCOSMO survey (https://obswww.unige.ch/~lemon/tdcosmo-master/), which aims to measure the expansion rate of the Universe (H0) using a novel technique based on strong gravitational lensing, time delay measurements, and stellar galaxy dynamics. This technique is independent of the ones used by supernovae and cosmic microwave background (CMB) observations, which currently disagree on the value of H0 and pose a "crisis" in cosmology (see here). By providing a new and precise measurement of H0, this project will try to resolve this tension and test the validity of the standard cosmological model.
As a DPhil student, you will work with a team of experts from different institutions and use data from the Hubble Space Telescope, JWST, and ground-based integral-field spectroscopy. You will learn how to model gravitational lenses, and galaxy stellar dynamics from spectroscopic data. You will also have the opportunity to participate in international conferences and workshops, collaborate with other researchers, and develop your skills in data analysis, programming, and scientific communication.
Supermassive Black Hole growth in merger-free galaxies
Supervisors: Rebecca Smethurst, Chris Lintott
It has long been thought that galaxy mergers lead to the majority of supermassive black hole (SMBH) growth, however cosmological simulations have recently shown that this is not the case. The majority of SMBH growth seems to occur through galaxy-merger-free processes, such as gas being funnelled to the central SMBH down a galaxy's spiral arms. However, these processes are understudied, and yet understanding the limitations to such growth mechanisms and the subsequent impact on the host galaxy through feedback of energy from the SMBH is crucial to our understanding of galaxy evolution as a whole. To isolate these merger-free mechanisms, galaxies with obvious disk morphologies hosting growing SMBHs are identified in large galaxy surveys. However, such a combination is rare, with less than 200 such systems currently known.
This project would see a student using Galaxy Zoo morphological classifications to select a larger sample of these merger-free galaxies from a range of galaxy surveys which provide deeper imaging (such as DeCALS, Euclid due 2025, and Rubin due 2026). The student would calculate both SMBH and galaxy properties using survey data to determine how they have co-evolved, along with writing proposals for observational follow-up time using state-of-the-art facilities (such as the VLT, E-ELT, ALMA and space based observatories such as HST) with the aim of understanding this understudied SMBH growth pathway. With DeCALS survey data readily available, a student could make rapid progress on this important problem.
The successful candidate will gain expertise in galaxy morphology, active galactic nuclei selection methods, data reduction and analysis. The student would have the option of being involved with the acquisition of Galaxy Zoo classifications using a mixture of volunteer and machine learning efforts. This project would suit a student who is interested in observational astronomy, and wants to acquire and analyse both imaging and spectroscopic data, and therefore may include visits to astronomical observatories around the world.
The project will be co-supervised by research fellow Dr. Rebecca Smethurst, who is an expert on galaxy-merger-free SMBH growth (Smethurst et al. 2021, 2023) and Prof. Chris Lintott, who pioneered the use of volunteer and machine galaxy morphology classifications.
Fingerprinting the first generation of stars
Supervisors: Julien Devriendt, Adrianne Slyz, Harley Katz
The properties of the first generation of pristine, heavy element-free stars (called Population III stars) are a mystery: little is known about when they started and stopped forming, the range of masses they span at birth (their Initial Mass Function), and the quantity of various elements they return to the interstellar and intergalactic medium. With the launch of the James Webb Telescope and a number of powerful telescopes, e.g. HARMONI on the ELT on the horizon, the prospects of directly observing this first generation of stars have considerably improved.
However, another compelling way to track these first stars is to look for their remnants. When Pop III stars reach the end of their lifetime, depending on their mass they either explode as supernovae or collapse directly into a black hole. Mergers of these remnants, neutron stars or black holes, produce gravitational wave signals that can be picked up by space-based and ground-based detectors (LISA, Advanced LIGO). Whether Pop III black hole binary systems contribute significantly to the gravitational wave background depends on their mass and redshift distribution, something that requires detailed modelled predictions.
This DPhil project will explore where Pop III stars and their remnants end up, to deliver predictions of optimal places to search for them in the local Universe, across a range of wavelengths (from ultra-violet to radio). The student will analyse the MEGATRON simulation (PI Katz), the first cosmological simulation with a full non-equilibrium, primordial, metal, and molecular chemistry network coupled to on-the-fly radiation hydrodynamics. The simulation includes a state-of-the-art Pop III star formation model, with the first Pop III stars forming at redshift 28 when the simulation has ~1 pc spatial resolution, sufficient to capture the cooling of molecular hydrogen in a metal-free environment. Figure shows an output from the MEGATRON simulation at z=19.5. Purple is gas density, white is Lyman-Werner radiation, and red/yellow is gas temperature. There will also be scope for the student to design and run their own cosmological simulations as a way to refine the analysis.
Key questions to be answered include: Where do low mass Pop III stars end up versus the remnants of high mass Pop III stars? Is there a difference with one kind of Pop III star preferring the galactic halo and another the galactic bulge? What fraction of Pop III remnants form binaries and where do they end up? What is their contribution to the gravitational wave background? Where do the low mass Pop II stars that were enriched by heavy elements produced by a single Pop III supernovae end up in the Milky Way? What are their chemical abundance signatures?
Strong Gravitational Lenses
Supervisors: Aprajita Verma, Matthias Tecza
Collaborators: Anupreeta More (ICUAA, India), Phil Marshall (SLAC/Stanford USA, Visiting Lecturer at Oxford), Chris Lintott (Oxford)
The phenomenon of gravitational lensing, predicted by general relativity, produces some of the most spectacular astronomical images seen. A single galaxy, group or cluster of galaxies can act as "cosmic telescopes" distorting space-time. They can amplify and magnify the light of distant galaxies lying behind them into multiple images, rings or arcs. The separation or deflection of the lensed images is determined by the total mass (dark and light) of the foreground lensing galaxy and are therefore one of the most direct tracers of mass in the galaxies. In fact, strong gravitational lenses have a diverse range of astrophysical and cosmological applications including weighing galaxies and placing constraints of the Hubble constant and dark energy.
With the advent of the forthcoming Euclid and Vera C. Rubin Observatories, the field of strong gravitational lensing will be transformed as we enter regimes of hundreds of thousands of lenses. However, generating samples of strong lenses that are complete and pure is highly challenging. Even machine learning (ML) techniques yield samples that have high false positive rates (factors of 10-100). For Rubin & Euclid, a combination of ML discovery algorithms and crowd-assisted visual inspection, that is currently a highly successful means of discovering lenses, will form part of the early survey tasks.
This DPhil project includes work on lens finding and exploring the nature of the distant lensed high redshift galaxies. For lens finding, the student will work on ongoing Space Warps discovery projects including searches with current wide area surveys and preparations for Euclid and Rubin's Legacy Survey of Space and Time including exploring active learning. For the lensed background sources, the magnification and amplification due to lensing allow fainter galaxies to be studied on smaller scales than would be normally possible. This is a preview to the detailed galaxy science that will be achievable by the next generation of extremely large telescopes and we will explore expectations of what the ELT will achieve using simulations of lensed high redshift sources, multi-source lenses and/or lens substructure in collaboration with colleagues in Durham. The student will be expected to help and liaise with citizen lensing enthusiasts participating in Space Warps (Paper 1 and 2, NPR Science Friday on the HSC search).
Cosmology and astrophysics from multiple tracers of the large-scale structure
Supervisor: David Alonso
One of the main obstacles preventing cosmology from becoming a truly robust science of discovery is our lack of understanding of the complex astrophysical systems that underly almost all cosmological observations of the large-scale structure. Fortunately, a broad range of probes of this large-scale structure are now available to us that provide complementary information about the physical properties of these systems. In this project, we will explore combinations between several tracers of the large-scale structure (galaxy clustering, weak lensing, the Sunyaev-Zel'dovich effect, the Cosmic Infrared Background, X-ray and radio data) to construct a complete, data-driven, theoretical model, describing the impact of astrophysical processes (galaxy formation, gas virialisation, AGN feedback) in a cosmological setting. This work will have direct impact on current and future cosmological constraints from a variety of experiments, including the Simons Observatory and the Legacy Survey of Space and Time (LSST). Interested candidates should be keen on both data analysis and theoretical modelling, as well as statistics, coding, and maths.
Figure: reconstruction of the star formation history from a combination of Cosmic Infrared Background, galaxy clustering, and weak lensing data (Jego, Alonso et al. 2022).
Galaxy Evolution with the JWST: Tracing Star Formation and AGN activity across cosmic time
Supervisors: Dimitra Rigopoulou and Ismael Garcia-Bernete
Determining the mechanisms that regulate star formation, the growth of supermassive black holes (SMBH) and how these two processes evolve with time and galaxy mass is fundamental to our understanding of how galaxies form and evolve. Feeding and feedback form the new paradigm in galaxy evolution. Gas fuels the formation of stars, so when gas is removed due to outflows, the star-formation rate decreases. In some cases, outflows are so powerful and expel such large amounts of gas that they can completely halt star formation within the host galaxy. Outflows are the main mechanism by which gas, dust and elements are redistributed over large distances within the galaxy or can even be expelled into the space between galaxies – the intergalactic medium.
With its unparalleled sensitivity and unprecedented spectral and spatial resolution, the James Webb Space Telescope (JWST) is transforming our understanding of galaxy evolution, providing a much more detailed look at the physics of star formation, SMBH growth and their interplay in galaxies near and far. Ionic and atomic fine structure lines, rotational and vibrational H2 lines and dust emission features in the near and mid-infrared part of the spectrum can be used to infer the amount of recent and ongoing star formation, and measure AGN activity in a wide range of galaxies. Combining these new data with additional Atacama Large Millimetre Array (ALMA) CO observations, that probe the physical properties of the cold gas in and around galaxies and AGN, will enable us to identify the drivers and account for the physical processes that shape galaxy evolution from the early Universe to the present day.
We are looking for a motivated DPhil student to join our team. The candidate will employ JWST NIRSpec and MIRI spectroscopy to probe the impact of SMBH on the host galaxy in a sample of local Active Galaxies, using data that will be obtained as part of our successful JWST Cycle 2 observations.
I. Garcia-Bernete, D. Rigopoulou, A. Alonso-Herrero, et al., 2022, A&A 666, L5
I. Garcia-Bernete et al. , 2021, A&A 645, 21
D. Rigopoulou, M. Barale, D. Clary, et al., 2021, MNRAS, 504, 5287
Studying Hidden Nuclei with Principal Component Analysis Tomography
Supervisor: Dimitra Rigopoulou, Ismael Garcia-Bernete
Recent observations have uncovered the existence of extremely dusty nuclei in the centres of nearby infrared luminous galaxies. Hidden behind copious amounts of gas and dust the nature of these sources, whether a supermassive black hole (SMBH) or an unusual burst of star formation (SF), remains unknown. There is evidence that obscured growth in the past was even more important than today and that these obscured nuclei may represent a previously unknown phase of nuclear growth in the form of extremely obscured accreting SMBH and/or a highly compact starburst.
Observations with the James Webb Space Telescope (JWST) and its mid-infrared integral field spectrometer MIRI, cover a range of diagnostic features that offer a unique opportunity to unveil these hidden nuclei and make decisive progress in understanding their nature and more importantly their role in galaxy evolution. The mid-infrared part of the spectrum is particularly rich in spectral features that enable us to probe the nature of dust-obscured sources. Among those are ionic and atomic fine structure lines, pure rotational molecular lines and strong emission features at 3.3, 6.2, 7.7, 8.6, 11.3 and 12.7 μm, attributed to mixtures of Polycyclic Aromatic Hydrocarbons (PAHs).
However, analysis of the spectral signatures could be biased by prior prejudice on the origin of features and/or the complex nature and kinematics of the sources. Blind statistical techniques such as principal component analysis (PCA) consider the available information, find correlated features and separate them out into distinct components. PCA Tomography applied on calibrated JWST cubes will enable us to establish the nature of hidden nuclei in a robust way.
We are looking for a motivated DPhil student to join our team identifying these dust-obscured sources and studying their nature and properties. JWST/MIRI spectral cubes containing not only the spectral signatures but also information on the kinematics of the gas will be analysed using PCA Tomography.
Radiative transfer models and Bayesian spectral Energy Distribution (SED) fitting, will be used independently, to model the JWST spectra and compare the PC reconstructions to the model fits.
The study will enable an in-depth study of their physical properties in a statistically robust manner. These dusty objects are of key importance to galaxy mass assembly over cosmic time and studying them is fundamental to our understanding of galaxy evolution.
F. Donnan, I. Garcia-Bernete, D. Rigopoulou, et al., 2023, MNRAS, 519, 3691
F. Donnan, D. Rigopoulou, et al., 2022, A&A 669, 87
I. Garcia-Bernete, D. Rigopoulou, S. Aalto, et al., 2022, A&A, 663, 46
Contrasting simulations and observations: what can we learn about galaxy evolution with JWST and ELT-HARMONI
Supervisors: Niranjan Thatte, Dimitra Rigopoulou & Julien Devriendt
Cosmological simulations, like the New Horizon suite, can now achieve spatial resolutions of ~50 pc at redshifts z > 1, comparable to that achieved by the latest generation of mm/sub-mm telescopes (such as ALMA), space-based facilities (such as JWST) and soon to be achieved by the ELT+HARMONI at near-infrared wavelengths. This provides a unique opportunity to test predictions of galaxy evolution models by comparing “mock observations” of simulated galaxy properties with JWST and (in the near future) ELT+HARMONI observations.
We have used cosmological simulations (Figure 1 left & middle panels) that forward propagate primordial density fluctuations consistent with observations of the cosmic microwave background, to create individual galaxies at high spatial resolution, whose kinematic, morphology and dynamical properties are consistent with observed ensemble properties of the population at the corresponding redshift. As the input physics for the simulation is well understood, the resulting simulat provide dynamically stable mock galaxies consistent with physical laws and cosmological evolution models at the appropriate redshift.
We have developed a method for post-processing these mock galaxies, computing gas emission line intensities using CLOUDY radiative transfer computations in each cell, to get realistic model galaxy observations with self-consistent kinematics and dynamics.
We are looking for a motivated D.Phil student who is keen to use the results of state-of-the-art numerical simulations, and focus on comparing simulations with observations to test models of galaxy evolution. We are particularly interested in establishing the role of minor/major mergers in galaxy evolution and in particular their influence on the location of galaxies on the `main sequence’. The study will make use of JWST observations of a sample of z~2 galaxies showing a wide range of kinematics.
The successful candidate will gain expertise in radiative transfer, cosmological simulations, data reduction and analysis. The project work involves working with astronomical data sets, both real (JWST) and simulated.
Huang, J-S., et al., 2023, ApJ 949, 83
K. Grisdale, L. Hogan, D. Rigopoulou, et al., 2022, MNRAS, 513, 3906
L. Hogan, D. Rigopoulou, G. Magdis, et al., 2021, MNRAS, 503, 5329
N. Thatte, M. Tecza, H. Schnetler, et al., 2021, The Messenger, 182, 7
Superconducting Parametric Amplifier for Astronomy and Quantum Computing
Supervisors: Boon Kok-Tan and Dimitra Rigopoulou
The emergence of a new type of amplifier technology, the superconducting parametric amplifiers (SPAs), had drawn considerable attention from the astronomical, quantum computing and dark matter search communities. This is because SPAs can achieve quantum-limited sensitivity over a very broad bandwidth. They are compact, easy to fabricate with planar circuit technology, have ultra-low heat dissipation, and can potentially be integrated directly with other detector circuits. Their performance is far superior to the state-of-the-art cryogenic low noise amplifier used currently in fundamental physics experiments. These devices therefore can revolutionise ultra-sensitive instrumentation in astronomy and qubit technologies, from microwave to sub-millimetre (sub-mm) wavelengths. In particular, they can be used as readout amplifiers to improve the heterodyne receiver sensitivity significantly, and enable the construction of large bolometric arrays as a result of the negligible dissipation. Their large bandwidth, high power handling and quantum-limited noise performance will have a profound effect on quantum computing architecture and improve the fidelity to process hundreds of qubits, opening up the possibility of building a practical quantum computer and speeding up the searching speed of axion dark matter experiments.
This programme is comprising two complementary science topics. First, a focus on the development of the quantum amplifiers, and second an observation project.
On the instrumentation side, the student will start by studying the theoretical background along with learning to use commercial electromagnetism software to design the amplifiers. The student will then have the chance to get involved in the fabrication of the devices using state-of-the-art clean room facilities, either here in Oxford, or with our other collaborators (Paris, Chalmers, IRAM etc). The student will also learn how to use the sub-Kelvin cryogenics system and other experimental techniques, for measuring the performance of the amplifiers. In particular, the student will investigate the amplifier sensitivity and gain dependence on both the temperature and the losses of superconducting materials. Finally, the student will integrate the amplifier into an existing astronomical receiver/quantum computing receiver and assess the impact on the receiver's performance.
Observationally, the student will be expected to work on a Galaxy Evolution project focusing on dusty infrared (IR) luminous galaxies. This project focuses on the molecular gas content of IR luminous galaxies and in particular the link between gas content, Star Formation Efficiencies (SFE) and kinematics stage of the galaxies. The project involves reduction and analysis of spectroscopic data from large millimetre and submillimetre observatories, in particular NOEMA and ALMA.
The Superconducting Quantum Detector Group in Oxford have a well-equipped laboratory, with all the required instruments to perform the design and test of the amplifiers. He/she will also be assisted by an experienced technician, working along with post-docs and other DPhil students in the group, with the support from the electronics, mechanical and photo-fabrications expertise in Oxford Physics.