School of Physics & Astronomy

Find a PhD Project Here

Opportunities for fully funded PhD or EngDoc research projects are available in all fields of research within the School. You may search for current projects on this page. APPLY HERE for a PhD Place.

 PhD in Photonics
 PhD in Condensed Matter
 PhD in Astrophysics

Search current PhD opportunities in the School of Physics & Astronomy:-




Astrophysics

Galactic Dark Matter Effects from New Physics of Modified Gravity or Dark Energy
Zhao, Dr Hongsheng - hz4@st-andrews.ac.uk

We explore alternatives to the Cold Dark Matter framework by adding new physics in Dark Matter.
The new physics could include Modified Gravity or matter with fifth force interactions.
Several rare coincidences of scales in standard particle physics
are needed to explain why the negative pressure of the cosmological dark energy (DE)
(i) coincides with the positive pressure of random motion of dark matter (DM) in bright galaxies,
(ii) is within order of magnitude of the energy density of neutrinos, if it is allowed to have a mass of eV.
(iii) why Dark Matter in galaxies seems to follow the Tully-Fisher-Milgrom (MOND) relation of galaxy rotation curves, rather than the CDM predicted profile.
The aim is to link empirical dark matter constraints in galaxies with the cosmology.
The work can be purely theoretical using the Euler-Lagrangian approach. Or empirical by fitting galaxy velocity distributions and Gravitational Lensing data.
A bad case of split personality
Jardine, Prof Moira - mmj@st-andrews.ac.uk

Recent studies of the magnetic fields of very low mass stars shows a strange and so far unexplained behaviour. Some have strong, simple magnetic fields, and some have much weaker, complex, solar-like field magnetic fields. We do not fully understand why this difference occurs, but this project involves using the maps of the magnetic fields of these star to explore the physics of their coronae and winds and to examine the impact on any orbiting planets.
A complete census of rapidly quenching galaxies over cosmic time
Wild, Dr Vivienne - vw8@st-andrews.ac.uk

It has been known since the 1920's that most local galaxies can be morphologically classified as spirals or ellipticals. In the last century advancing galaxy surveys have demonstrated that morphology strongly correlates with many other galaxy physical properties: spiral galaxies are typically forming stars, contain cold gas and dust, live in less dense environments, and have modest-sized central black holes, whereas elliptical galaxies are “quenched” (not forming stars), surrounded by hot gas, live in denser environments, and have larger black holes. Despite precise statistical characterisation of these properties throughout much of cosmic history, the underlying physics that separates galaxies into star forming vs. quenched, with all attendant correlations, remains unclear. Understanding the *pathways* by which galaxies quench is a crucial outstanding question at the heart of modern galaxy formation and evolution, impacting a range of astrophysical studies from star formation and interstellar medium to dark matter and dark energy.

In this project we will combine the analysis of optical/NIR photometry and spectroscopy to identify and characterise the properties of rapidly quenched galaxies from redshifts of 0 to 2 in the real and simulated Universes. Then we will study their environment and gas properties to identify trends that should be reproducible in advanced cosmological hydrodynamic simulations. Comparison of data and simulations will elucidate the role of rapid quenching in the build up of the red sequence.

This project will work closely with Romeel Davé in Edinburgh (rad@roe.ac.uk), who runs the SIMBA and MUFASA galaxy evolution simulations. Real and mock data is in hand to commence the project. During the lifetime of the project new data will become available from the MIGHTEE survey (HI and radio SFRs) and VLT/MOONS (rest-frame optical spectroscopy of redshift 1-2 galaxies).

References
========

MIGHTEE: https://arxiv.org/abs/1709.01901
MOONS: https://www.eso.org/sci/facilities/develop/instruments/MOONS.html

http://adsabs.harvard.edu/abs/2018MNRAS.473.1168R
http://adsabs.harvard.edu/abs/2016MNRAS.463..832W
http://adsabs.harvard.edu/abs/2017MNRAS.471.1671D
Angular momentum loss and mass loading of stellar winds - slingshot prominences in action
Jardine, Prof Moira - mmj@st-andrews.ac.uk

Many solar-like stars show cool, dense clouds of gas trapped within the million-degree plasma of their outer atmospheres (or coronae). These so-called ``slingshot prominences'' carry away angular momentum when they are ejected and also are also responsible for mass-loading of the stellar wind. As a result, they may form an important part of the spin-down of young stars, and their impact on orbiting planets may lead to enhanced stripping of the planetary atmosphere.
Annihilation of Dark Matter
Zhao, Dr Hongsheng - hz4@st-andrews.ac.uk

A main diagnostic of the particle dark matter is its annihilation rate, which depends sensitively on the dark matter density profile. The student will explore various density models of the dark matter, taking into account the effects of black holes and baryonic dynamics.
Charging of dust grains and lightning in discs
Woitke, Dr Peter - pw31@st-andrews.ac.uk

Dust grains in protoplanetary discs generally charge up via photo-effect, electron attachment, and charge exchange reactions with molecular ions. Grain-grain collisions can possibly lead to an additional statistical charging (contact electrification), which has not yet been thoroughly discussed in the disc community yet (see e.g. Muranushi 2010). If grains of different sizes collide, charge up size-dependently, and move selectively (by gravitational settling), a large-scale charge separation could build up, leading to lightning in discs. This scenario has been proposed to explain intra-cloud lightning observed in volcano plumes, as well as lightning in the Earth’s atmosphere and in exo-planets (Helling et al. 2016). Similar effects could take place in protoplanetary discs, causing radio emission and having a long-term impact of the chemical composition of the gas.

* What is the size-dependent charge distribution of dust grains as function of position in the disc?
* What is the impact of grain charge on chemistry? Are there observational consequences, for example emission lines from molecular ions?
* Can the gravitational settling of charged grains build up electrostatic fields in discs?
* Can this field overcome the break-down field to cause spontaneous discharge processes (lightning)?
* Could lightning have a long-lasting impact on the chemistry in the planet-forming region?

The PhD-student is expected to implement triboelectric charging rates into ProDiMo, using typical turbulent dust velocities from MHD disc models. The resulting charge distribution of the grains will be studied depending on size and location in the disc, and consequences for large-scale electrification and lightning in discs shall be discussed.

Muranushi 2010: http://adsabs.harvard.edu/abs/2010MNRAS.401.2641M
Helling+2016: http://adsabs.harvard.edu/abs/2016SGeo...37..705H
Thi+2018: http://adsabs.harvard.edu/abs/2018arXiv181108663T
Determining the origins of galaxy bimodality using hierarchical Bayes methods
Wild, Dr Vivienne - vw8@st-andrews.ac.uk

How galaxies form and evolve is one of the outstanding questions of modern astrophysics. We have known for many decades that massive galaxies come in two main types - elliptical/quiescent and spiral/star-forming. However, it remains largely unknown why some galaxies are still forming stars while others are "red and dead". Extremely large galaxy surveys are providing an increasingly detailed census of both local and distant galaxies. Considerable progress is being made on quantifying the changing demographics of the galaxy population over the majority of the age of the Universe, but significant improvements in methods are required to dramatically improve our understanding of the physics behind the observable properties of galaxies.

In the last decade a Bayesian approach to the fitting of sophisticated models to high quality spectra and/or multiwavelength photometry has become common place in the analysis of galaxy spectral energy distributions (SEDs) at all redshifts (Walcher et al. 2011). The result is robust physical properties, such as galaxy stellar mass, dust content and star formation history, together with well quantified degeneracies between these parameters. However, by treating galaxies as independent entities to determine their physical properties, we are missing vital population information. A better approach would be to treat galaxies as a population of objects with a common origin and common underlying variables. This could tighten constraints on the physical properties of individual galaxies as well as the underlying relationships that impact the life of galaxies. It could also allow us to extract information from larger surveys with lower quality observations.

Hierarchical Bayes techniques have been used in the astronomical literature to solve problems as diverse as quasar redshift estimation (Bovy et al. 2011), exo-planet orbit analysis (Hogg et al. 2011), properties of supernovae light curves (Mandel et al. 2009), and photometric redshifts (Leistedt et al. 2016). They differ from standard Bayesian methods by fitting the entire dataset in a coherent manner, instead of single objects as entirely independent entities. By applying these methods to galaxy evolution studies, we will improve our ability to break degeneracies between physical parameters and understand the underlying processes governing galaxy evolution. These methods could be applied to e.g. complete populations of galaxies in spectroscopic or photometric surveys, or entire integral field datacubes of single galaxies.

This interdisciplanary project will be jointly supervised by Drs Vivienne Wild and Michail Papathomas in the Schools of Physics and Astronomy and Mathematics and Statistics respectively. Dr Wild has built her career around developing and applying novel statistical techniques to explore datasets on galaxy evolution, focussing most recently on understanding the nature of post-starburst galaxies. Dr Papathomas is an expert in Bayesian modelling, both in the development of new methods and their application to a wide variety of datasets.

Large extragalactic datasets are already available for analysis, both at low and high redshift. The School of Physics and Astronomy is a member of the UK participation group in SDSS-IV, the fourth generation of Sloan Digital Sky Surveys, a large international collaboration encompassing several astronomical surveys. The methods developed during the project could also be applied to upcoming datasets to which the group has proprietary access such as DESI bright galaxy survey, LSST science verification data and VLT/MOONS near-infrared spectroscopic survey.

The project involves the development of statistical techniques to make them applicable to astronomical datasets. This project would suit students with a background in (astro)physics but strong aptitude for maths and statistics, and students with a background in maths or statistics and interest in astrophysics.

For more information please contact Dr Vivienne Wild and Dr Michail Papathomas (vw8@st-andrews.ac.uk, M.Papathomas@st-andrews.ac.uk).


References:
Bovy J., Myers A. D., Hennawi J. F. et al. arXiv:1105.3975
Hogg D. W., Myers A. D., Bovy J., 2010, ApJ, 725, 2166
Leistedt B., Mortlock D., Peiris H., 2016, MNRAS, 460, 4258
Mandel K. S.; Wood-Vasey W. M., Friedman A. S., Kirshner R. P., 2009, ApJ, 704, 629
Walcher C. J., Groves B., Budavri T., Dale D., Ap&SS, 2011, 331, 1

Surveys:
SDSS-IV www.sdss.org
LSST www.lsst.org
DESI www.desi.lbl.gov
MOONS https://vltmoons.org/science-2/

Diffuse ionized gas in galaxies
Wood, Dr Kenny - kw25@st-andrews.ac.uk

Extensive layers of diffuse ionized gas are observed in the Milky Way and other galaxies. This project will study the structure, ionization, heating, and dynamics of diffuse ionized gas using our newly developed radiation hydrodynamics codes that incorporate feedback processes including photoionisation, stellar outflows, and supernovae. Output from our 3D rad-hydro simulations will be compared with emission line observations of the diffuse ionised gas.
Dissecting galaxies in transition
Wild, Dr Vivienne - vw8@st-andrews.ac.uk

The number density of `red and dead' elliptical galaxies increases with cosmic time, meaning galaxies must be transitioning from star-forming disks. In this project we will use the SDSS-IV MaNGA integral field survey alongside mock observations of hydrodynamic simulations to move beyond demographics and pin down which physical processes are responsible for this transition, as a function of stellar mass and environment.

Massive galaxies in the nearby Universe typically fall into two distinct populations (e.g. Strateva et al. 2001; Baldry et al. 2004): actively star-forming disk galaxies, and `red and dead' elliptical galaxies with little or no signs of ongoing star formation. The bimodality in the star-forming properties of massive galaxies has existed since at least z~2 (Tomczak et al. 2014), and the strong correlation between star-forming properties and morphology holds to a similar epoch.

The increasing number density of red-sequence galaxies with cosmic time at fixed stellar mass (e.g. Moutard et al. 2016) tells us that galaxies move from the blue-cloud to the red-sequence by having their star formation halted (`quenched'). Coincidentally, the typical star formation rate of galaxies decreases as they exhaust their gas supplies, but this process is unable to account for the alteration in the galaxies' morphologies. Many different mechanisms have been proposed to partly or wholly explain the build-up of the quenched elliptical population with time, such as gas stripping, merger induced starbursts, AGN feedback and morphological quenching.

Catching galaxies that are in the act of transition, and studying both their evolving demographics and their properties in detail, alongside mock observations from state-of-the-art simulations, are the ways to make further progress (Wild et al. 2009). These objects are rare, and only recently have surveys been large enough for us to be able to constrain the number density evolution of green-valley and post-starburst galaxies, alongside the quiescent galaxies we expect them to evolve into.

The advent of highly multiplexed integral field surveys, alongside well developed hydrodynamic galaxy simulations, means the time is perfect for a fully encompassing study of all types of candidate-transition galaxies. The fossil record of a galaxy's formation history is encoded in its morphology, stellar kinematics, stellar populations and dust, ionised gas content and kinematics. The MaNGA survey provides access to all of these, alongside robust control samples, volume correctable number densities, a wide range of environments and stellar masses. Importantly, comparison to large numbers of hydrodynamic simulations is now possible, converted into mock data cubes to be analysed in exactly the same way as the data.

In this project we will perform an integrated analysis of the morphologies, shapes, spatially resolved kinematics and stellar populations of the largest ever sample of local post-starburst, blue-ellipticals, red-spirals and green-valley galaxies observed with an integral field unit, alongside large sets of control samples and hydrodynamic simulations. We will aim to understand what are their ancestors and descendants and thereby understand whether they are truly transitioning populations, and on what timescales. We will use these results to interpret data from high-redshift surveys, where post-starburst galaxies are far more common and potentially important for building the present-day galaxy bimodality (Wild et al. 2016).

This project will be co-supervised with Dr Anne-Marie Weijmans, lead observer for MaNGA.

Strateva et al. 2001, AJ 122, 1861
Baldry et al. 2004, ApJ 600, 681
Tomczak et al. 2014, ApJ, 783, 85
Moutard et al. 2016, A&A, 590, 103
Wild et al. 2009, MNRAS, 395, 144
Wild et al. 2016, MNRAS, 463, 832
MaNGA survey : http://www.sdss.org/surveys/manga/
Echo Mapping of Black Hole Accretion Flows in Active Galactic Nuclei
Horne, Prof Keith - kdh1@st-andrews.ac.uk

This project qualifies as an STFC studentship in Data-Intensive Science.

Light travel time delays enable micro-arcsecond mapping of accretion discs and broad emission-line regions around the super-massive black holes in the nuclei of active galaxies. Using our share of time on the LCOGT robotic telescope network, along with data from HST, Swift and Kepler satellites, we are monitoring spectral variations of Active Galactic Nuclei to measure black hole masses, accretion rates, and luminosity distances. By decoding information in the reverberating emission-line profiles, we make 2-dimensional velocity-delay maps of broad emission-line regions, mapping the velocity field and ionisation structure of the accretion flows. The student will acquire and analyse such datasets, fitting parameterised models using MCMC methods, image reconstruction using Horne maximum entropy fitting code MEMEcho, and photo-ionisation codes such as Ferland's Cloudy.
Feedback in young stellar clusters
Cyganowski, Dr Claudia - cc243@st-andrews.ac.uk

Most stars form in clusters, where energetic feedback from massive
(proto)stars--including outflows, ionization, heating, and
winds--shapes the environment and impacts accretion. The relative
importance of different feedback processes is a key outstanding
issue in our understanding of massive star formation.

The aim of this project is to conduct the first large-scale
observational study of the role and physics of feedback in massive
(proto)clusters. This will involve analyzing high-resolution data
from recently-upgraded (sub)mm and cm-wavelength interferometers, in
particular the Submillimeter Array (SMA), the Jansky Very Large Array
(VLA), and, potentially, the Atacama Large Millimeter/sub-millimeter
Array (ALMA). The observational results will be compared with
simulated observations of numerical models of massive star and
cluster formation.
Feedback processes in star forming regions and the interstellar medium
Wood, Dr Kenny - kw25@st-andrews.ac.uk

This project will use (and futher develop) our new radiation hydrodynamics codes to syudy the effects of stellar feedback on the structure, dynamics, and star formation rates in star forming regions (parsec sizescales) and the interstellar medium (kiloparsec sizescales). Feedback processes that are readily incorporated into our codes include photoionisation, radiation pressure, dust heating, stellar outflows, and supernovae. In addition to studying these processes in star forming regions, the new numerical codes are also applicble to numerical studies of galactic outflows and the impact of feedback processes and leakage of ionising radiation into the intergalactic medium.

Informal enquiries to Kenny Wood: kw25@st-andrews.ac.uk
Irradiated brown dwarfs in the galaxy
Helling, Dr Christiane - ch80@st-andrews.ac.uk

Brown dwarfs are very low-mass stars which are as cool as planets. In contrast to planets, most of the brown dwarfs are fast rotators with strong magnetic fields causing strong radio emission to emerge. The origin of this radio emission is largely unsolved but must be linked to the atmospheric environment somehow. This project therefore focuses on the 3D structure of brown dwarf atmospheres under the effect of external irradiation. External irradiation will ionise the upper atmosphere but also affect the energy budget of the underlying and cloud forming atmospheric regions.

The aim of this project is to develop a 3D climate model for brown dwarfs under the effect of external irradiation in order to study for the first time the interior of a 3D brown dwarf atmosphere as well as the possibility of the emergence of a chromosphere environment. First, we will study a generic set up, but will apply this model to white dwarf - brown dwarf binaries and free-floating brown dwarfs in different galactic environments.
Lightning in Exoplanets
Helling, Dr Christiane - ch80@st-andrews.ac.uk

Extrasolar planets have proven to be far more diverse than the planets in the solar system. This project will study lightning in extrasolar giant-gas planets based on the premisses that lightning has been observed for most of the solar system planets.

This project utilises 3D climate simulations that self-consistently include cloud formation in chemically different environments. The aim of the project is to study lightning in the 3D atmospheres of the well-studied case of giant gas planets (e.g. HD189733b). The project will also study ionisation processes in exoplanet atmospheres that may lead to the formation of an ionosphere. Lightning may provide a new window into the dynamic atmospheres of extrasolar planets which so far is observed as an unresolved dot in the sky. This project is timely linked to the launch of JWST, the largest IR and near-IR space telescope in years to come.

Mass Distribution of the Galaxy
Zhao, Dr Hongsheng - hz4@st-andrews.ac.uk

The mass distribution of the Galaxy is being / will be mapped out in great detail in the next decade with the numerous surveys of the Galaxy, including Segue, RAVE, GAIA, and completed ones like 2MASS, DENIS. A model for the potential and phase space of the galaxy is essential to bring various pieces of information together. The student will develop such models building on experience from existing models.
Mocking the Universe using machine learning
Tojeiro, Dr Rita - rmftr@st-andrews.ac.uk

Computer simulations play an increasingly crucial role in observational cosmology and galaxy evolution. Cosmological hydrodynamical simulations and semi-analytic models have helped us understand what physical processes might be influencing the formation and growth of galaxies, and large N-body simulations have played crucial roles in helping us test methodologies in large-scale structure studies. As surveys increase in size, and as we turn our attention to more subtle effects in galaxy evolution (e.g. environment), we require a large suite of simulations that can help us test our ambitious observations. The requirements of these simulations, namely a large volume and substantial physical complexity, make this a difficult task.

This project will advance the use of neural networks as a way to create mock surveys from large N-body simulations by using cosmological hydrodynamical and semi-analytic simulations as training sets. You will work within the DESI team and produce simulations to support the analysis of DESI data. According to your personal interests, you will then have the opportunity to use your simulations to investigate DESI data to its full potential.
New physics for Dark Matter via Modified Gravity/Dark Energy

We explore alternatives to the Cold Dark Matter framework by adding new physics in Dark Matter.
The new physics could include Modified Gravity or matter with fifth force interactions.
Several rare coincidences of scales in standard particle physics
are needed to explain why the negative pressure of the cosmological dark energy (DE)
(i) coincides with the positive pressure of random motion of dark matter (DM) in bright galaxies,
(ii) is within order of magnitude of the energy density of neutrinos, if it is allowed to have a mass of eV.
(iii) why Dark Matter in galaxies seems to follow the Tully-Fisher-Milgrom (MOND) relation of galaxy rotation curves, rather than the CDM predicted profile.

The work can be purely theoretical using the Euler-Lagrangian approach. Or empirical by fitting galaxy velocity distributions and Gravitational Lensing data.
New Physics for Galactic Dark Matter via Modified Gravity/Dark Energy

We explore alternatives to the Cold Dark Matter framework by adding new physics in Dark Matter.
The new physics could include Modified Gravity or matter with fifth force interactions.
Several rare coincidences of scales in standard particle physics
are needed to explain why the negative pressure of the cosmological dark energy (DE)
(i) coincides with the positive pressure of random motion of dark matter (DM) in bright galaxies,
(ii) is within order of magnitude of the energy density of neutrinos, if it is allowed to have a mass of eV.
(iii) why Dark Matter in galaxies seems to follow the Tully-Fisher-Milgrom (MOND) relation of galaxy rotation curves, rather than the CDM predicted profile.

The work can be purely theoretical using the Euler-Lagrangian approach. Or empirical by fitting galaxy velocity distributions and Gravitational Lensing data.
Star formation in dwarf galaxies
Bonnell, Prof Ian - iab1@st-andrews.ac.uk

This project is to develop the first models of resolved star formation on galactic scales. This will involve modelling a full galactic potential and how it drives the formation of molecular clouds and the onset of gravitational collapse and star formation. feedback from ionisation and supernova will be included to assess molecular cloud lifetimes and star formation efficiencies.
Star-Planet Interaction
Jardine, Prof Moira - mmj@st-andrews.ac.uk

Tau Boo is the only star for which we have been able to track the full cyclic reversal of the stellar magnetic field. This system is also well-known, however, because it hosts a Hot Jupiter that is so close to the star that it may lie within the stellar corona. What is the nature of the interaction between the star and planet in this case and is it related to the puzzling nature of the very short magnetic cycle? This project will investigate tau Boo and other similar star-planet systems.
Triggering of star formation
Bonnell, Prof Ian - iab1@st-andrews.ac.uk

There are several outstanding issues in current models of star formation. One of these is the role of feedback from young stars in producing subsequent generations of young stars. Triggering of star formation through supernova events is likely to be the dominant mechanism. Numerical simulations of SNII impacting on molecular clouds and the triggering of star formation will be used to develop physical models, and ultimately observational predictions and tests of the process.
Unveiling the role of environment on the growth of galaxies and dark-matter halos with DESI
Tojeiro, Dr Rita - rmftr@st-andrews.ac.uk

One of the challenges in galaxy evolution is to understand the evolutionary paths of different types of galaxies. Although stellar mass (observationally) and halo mass (in simulations) display a dominant role in the formation and evolution of galaxies, the role of environment is less well-understood. This is largely due to the difficulty in defining “environment”, and in estimating it from observations.

This project will use data from the forthcoming DESI survey to investigate the role of environment in the local Universe with unprecedented clarity. DESI will observe a high-density, high-completeness sample of galaxies out to z=0.4 over 14,000 sq degrees, starting in 2020. By combining this exquisite dataset with SDSS data and deep imaging, you will investigate the role of environment for a variety of physical estimators (such as overdensity over a variety of scales, satellite/central classification and cosmic web estimators), and understand the implications for the evolution of halos, galaxies and the galaxy-halo connection.
Viscous heating in protoplanetary discs
Woitke, Dr Peter - pw31@st-andrews.ac.uk

D’Alessio et al. (1998) have established that the viscous dissipation of gravitational potential energy that is released when young stars accrete mass through a disc can lead to a temperature inversion in the midplane of these discs. Since then, radiative transfer methods have been sufficiently improved to include that effect in a rigorous way (for example Min et al. 2011). In this work, we want to thoroughly study the impact of viscous heating on the disc structure of class II T Tauri stars, and to critically evaluate in how far this effect is important for the correct interpretation of near-mid molecular infrared emission lines that have been observed by Spitzer/IRS, and will be observed again with JWST/MIRI with higher spectral resolution and better signal/noise.

The work will be part of ongoing efforts to improve the disc modelling software ProDiMo (e.g. Woitke+2016, Woitke+2018), where applicants are expected to bring keen interest and experience in programming.

* improve the treatment of continuum radiative transfer in ProDiMo
* study the effects of viscous heating on the internal gas and dust temperature structure in protoplanetary discs
* calculate the hydrostatic structures of TTauri discs including viscous heating
* predict the near-infrared line emission of T Tauri discs including viscous heating
* conclude about the icelines in protoplanetary discs as affected by viscous heating

D’Alessio+1998: http://adsabs.harvard.edu/abs/1998ApJ...500..411D
Min+2011: http://adsabs.harvard.edu/abs/2011Icar..212..416M
Woitke+2016: http://adsabs.harvard.edu/abs/2016A%26A...586A.103W
Woitke+2018: http://adsabs.harvard.edu/abs/2018A%26A...618A..57W