Dissertation projects for the MSc by Research in Astronomy & Astrophysics
Below are some of the MSc(R) projects for this coming year (2015/2016). We will try to keep this list updated, particularly on the lead up to the beginning of the first semester (21st September 2015, with induction the week before). However, we encourage prospective MSc(R) students to speak with as many of our academic staff, as early as possible, to find out what we do and to see if there are possible MSc(R) projects available - this list is unlikely to be comprehensive. Note that supervisors and projects should be decided within the first 1-2 weeks of the first semester and they should inform the MSc(R) course director (Dr. Clive Dickinson).
e-MERLIN studies of compact ultra-steep spectrum sources.Supervisors: Dr Megan Argo & Dr Rob Beswick
Ultra-steep spectrum (USS) sources are an enigmatic class of object. Defined as having unusually steep radio spectra and compact morphologies on arcsecond scales, these sources are generally not detected outside the radio regime, and no redshift information is known, making them exceedingly difficult to classify. Suggestions for their nature include high-redshift radio galaxies located at or near the epoch of re-ionisation, pulsars, young obscured radio galaxies, and quasars with steep spectrum cores. So far, such sources have received little attention since the number of such sources observed has been too small to draw robust statistical conclusions, although with the advent of new telescopes such as LOFAR and MWA which are surveying large areas of the sky at low frequencies, many more examples of such sources are likely to be discovered in the near future. Whilst the nature of these sources is, as yet, unknown, recent VLBI observations of a small sample have shown that a significant fraction are compact on milli-arcsecond scales but with less than 30% of the flux recovered, suggesting that there is source structure on spatial scales to which the e-MERLIN array is best sensitive.
We have now been allocated observing time to investigate a much larger sample with e-MERLIN, and this project will focus on these observations. Selected from four large catalogues, we have a sample of 73 candidate sources which are compact on arcsecond scales and have low-frequency spectral indices <-1.3 between 74 and 330 MHz. Our aim is to observe the suitable candidates in this sample in order to examine their morphologies on intermediate spatial scales, confirm that their spectral indices stay steep at 1.4GHz, and create a sample of sufficiently compact sources for further VLBI follow-up. This new information will allow us to more thoroughly investigate this intriguing class of sources and narrow down the possibilities for their origin.
Variability of compact components in nearby starburstsSupervisors: Dr Megan Argo & Dr Rob Beswick
Starburst galaxies are so-named because they contain significantly elevated rates of star-formation which occur over a timescale much shorter than the lifetime of a galaxy. The large amounts of dust in such sources means that much of the activity is obscured from view at optical wavelengths. However high resolution radio observations are able to penetrate this material and view the active star-formation within. This project focusses on new radio observations of a particularly spectacular example of an interacting galaxy pair. In this case, an intruder has passed through another gas-rich galaxy, creating a vast ring of star formation. This ring displays different intensity variations in the optical, IR and UV, contains numerous powerful X-ray sources, and shows strong radio continuum emission at low resolution. While the intruder appears to be gas-poor, it also exhibits a ring morphology around the optically bright core. In contrast to the main ring, however, the intruder contains only one X-ray source, the core, which could be due to a weak AGN or an interaction-induced nuclear starburst. This project will use recently obtained high-resolution e-MERLIN observations to examine the components in the starburst ring, search for supernova remnants and HII regions to get a handle on the star formation, investigate the nature of the core emission in both the main ring and the companion galaxy, and investigate the nature of the ULX sources.
The relation of radio emission to other star formation tracers in the spiral galaxy M83Supervisors: Dr George Bendo & Dr Rob Beswick
Luminous blue stars in star forming regions produce large amounts of ultraviolet radiation. Star formation rates are measured by looking for signs of these short-lived blue stars, including measuring the ultraviolet light from the stars themselves, the optical and near-infrared spectral line emission from hydrogen gas ionised by the ultraviolet light, and the mid-infrared emission from interstellar dust heated by the blue stars. About 10-30 million years after forming, these blue stars will explode as supernovae, producing substantial synchrotron emission at radio wavelengths, and this radio emission can also be used to measure star formation rates.
Radio emission is well-correlated with other star formation tracers for other galaxies. When looking at sub-kiloparsec sized regions, radio emission appears more diffuse and extended compared to other star formation tracers, but the emission appears in the same place as other star formation tracers. This is because most locations where this correlation has been examined are places where the supernovae have not travelled far from where they formed. In grand design spiral galaxies, however, we see gas that fuels star formation flowing into one side of the spiral arms, star formation itself occuring within the spiral arms, and young stars emerging out of the other side. We would therefore expect the radio emission from supernovae to appear offset from other star formation tracers in these types of spiral galaxies.
The analysis in this project is focused on comparing the ultraviolet, H alpha, mid-infrared, and radio emission from M83, a nearby grand design spiral galaxy with strong star formation and supernova activity. The goal is to determine whether it is possible to see this predicted offset between radio emission and the emission from the other star formation tracers.
Molecular gas in ULIRG-to-QSO transition objectsSupevisors: Dr. Robert Beswick & Dr Jeff Wagg (SKA Organisation)
Since the early surveys of FIR continuum emission in ultraluminous infared galaxies with IRAS, it has been believed that some galaxies go through a heavilly dust obscured starburst phase before emerging as an optically luminous quasar. These have termed the ULIRG-to-QSO transition objects. The initial burst of star-formation is thought to be the product of a gas-rich merger. However, recent years have seen the emergence of a new picture, where gas-poor galaxies containing an active galactic nucleus, can be `refueled' by mergers with gas-rich galaxies. Sensitive interferometers observing at mm-wavelengths allow us to isolate the source of the molecular gas in these systems previously classified as ULIRG-to-QSO transition objects.
We have completed an interferometer survey of CO line emission in a sample of ULIRG-to-QSO transition objects using the Combined Array for Research in Millimeter-wave Astronomy (CARMA). All of these sources benefit from high sensitivity imaging from the Hubble Space Telescope. A student would work on the CARMA data in order to learn the fundamentals of mm-wavelength interferometry and produce maps of the mm-wavelength CO line emission. It is expected that a research publication would be produced as a result of this analysis.
Neutron star formation through electron-capture supernovaeSupervisor: Dr Rene Breton
The classical formation channel of a neutron star is the core-collapse of a massive star as a supernova. In recent years, there has been tantalising evidence from the properties of some pulsar binaries that a fraction of the neutron star population might form via electron capture supernovae. In this scenario, a 7-10 Msun star building a degenerate ONeMg core collapses as the capture of electrons by magnesium causes a sudden lost of hydrostatic pressure. Such an event would also leave behind a neutron star but its mass would likely be lower than via the traditional channel. In addition the electron-capture scenario may impart a much smaller kick to the neutron star, which could explain why some double neutron star systems are in circular rather than eccentric orbits.
This project will explore the formation of neutron stars through electron capture supernovae. Using stellar evolution codes, such as MESA, the student will investigate the conditions leading to an electron capture event and their effects on the resulting neutron star, such as its mass and spatial velocity. The candidate will also look at how the evolution in a binary system may increase/decrease the odds of a star becoming a neutron star through this channel, which has implications, among other things, for survival rate of binary systems and the retention of neutron stars in globular clusters. The project has broad implications for our understanding of binary evolution, the pulsar population, and the calculation of the rate of double neutron star mergers which are a primary source of gravitational waves to be observed with LIGO.
Measuring the dark universe using gravitational lensingSupervisor: Prof Sarah Bridle
The Dark Energy Survey is an international project to measure the shapes and positions of 300 million galaxies over 1/8th of the sky. It started in 2013 and will run for five years. It has been designed to find out the nature of the "dark energy" which has been proposed to explain the mysterious acceleration of our Universe. It brings together four complementary investigation methods on one telescope and Prof. Bridle is Co-Coordinator of work on one of these methods: weak gravitational lensing. Weak lensing is the apparent distortion of distant galaxies due to the bending of light by intervening matter. It allows us to build up a three-dimensional map of the dark matter from which we can learn about the dark energy.
This MSc project would run for the most exciting part of the survey, at the time of the biggest increase in data volume over the next years in cosmology. The majority of the work will likely be focussed on disentangling the cosmological lensing effect from the effects of distortions in the telescope optics and the processes in galaxy formation. This will be mainly computational work. The MSc student will work together with Prof. Bridle, Dr. Zuntz and PhD student Niall Maccrann.
Gravitational Lensing with the Dark Energy SurveySupervisor: Prof Sarah Bridle
This project will test and use the galaxy shapes measured on the Dark Energy Survey data. It will help improve the im3shape shear measurement pipeline by comparing results using different settings, and implementing calibration corrections. The student will perform statistical tests to determine the level at which the telescope point spread function is contaminating the shear measurements. The student will then measure the mass of a cluster of galaxies by model fitting.
Horns and polarizers for the L-Band All-Sky Survey (L-BASS)Supervisors: Prof. Ian Browne, Prof. Peter Wilkinson, Co-supervisor: Prof. Clive Dickinson
L-BASS is a project to make a high precision map of the sky at a frequency around 1420MHz (L-band). There are both technical and astrophysical motivations for the project. The technical one is that for L-BASS, and for a related project BINGO, large horns with very low sidelobes and excellent polarization characteristics need to be constructed. Fabrication of such horns using conventional methods would be impossibly expensive. However, a new technique has been pioneered at Jodrell Bank in which the horns are constructed out of sheets of inexpensive insulation foam stacked to produce the required shape. A half-sized horn has already been made and shown to have excellent performance. The two horns being constructed for L-BASS will be the largest made using this technique and, if these horns live up to expectations, the same fabrication technique will be used for 50+ horns for BINGO, thus saving the project approximately $1 million. In terms of astrophysics, the L-BASS absolutely calibrated map of the sky is required to improve the separation of Galactic foreground emission from that of the cosmic Microwave Background as well as for Galactic science. In addition, our map will test the intriguing claim (Seiffert et al.) that there is an unexplained new component to the radio emission at these low frequencies.
The project is to characterize the properties of two large horn antennas and then help mount them so that an absolutely calibrated map of the sky can be made. The electrical properties of the horns will be measured in the laboratory and then their polar diagrams will be measured using a test range at Jodrell Bank. In parallel, waveguide-polarizers will be built which convert the output from the horns to opposite hands of circular polarization, something that is required because the emission from the sky is linearly polarized. By observing in circular polarization the received signal does not depend on the orientation of the antenna. The polarizers will need to be tuned in the lab using a vector network analyser. Finally the horns, polarizers and an existing radio receiver will be integrated and mounted on a prepared site at Jodrell Bank Observatory and the overall performance of the system characterized.
Heating the solar corona: 3D numerical magnetohydrodynamic simulations and 1D modelling of the turbulent dynamoSupervisor: Prof Philippa Browning
A major unsolved problem in astrophysics is to explain why the solar corona is at a temperature of over a million degrees Kelvin (compared with a surface temperature of about 6000 K). Coronal plasma is believed to be heated by dissipation of stored magnetic energy. Much research concerns modelling the dissipation of magnetic energy through the process of magnetic reconnection. There are two potential projects in this area. One project will involve running numerical simulations using the LARE3D code, which numerically solves the equations of magnetohydrodynamics, and analysing the results. This will build on recent work showing that reconnection can be triggered by the onset of the kink instability in twisted coronal loops, exploring a range of magnetic field configurations and exploring the energy release. The second project will use a simplified analytical model of the effects of turbulent reconnection, building on one-dimensional models widely used for laboratory plasmas in which the turbulence is parameterised as a 'dynamo' electric field. These models will be extended to solar coronal loops, requiring some analytical calculations and simple numerical modelling (solution of ordinary differential equations).
Simulations and forecasts for the Square Kilometre ArraySupervisor: Dr Michael Brown and Dr Anna Bonaldi
The Square Kilometre Array (SKA) is a multi-purpose radio telescope covering the frequency range from 70 MHz to >25 GHz. Construction will start in 2016 and finish in 2023, with first science to start in 2019. An important aspect prior to the operation is the forecast of performances for a given scientific objective and depending on the instrumental specifications. With application to the Epoch of Reionization research, one of the key science projects of the SKA, the student will work on simulations of the instrumental response and the accuracy of removal of point-like sources from the maps, depending on the array configuration and the other parameters describing the instrument and the observation.
High energy particles in solar flaresSupervisor: Prof Philippa Browning
Solar flares are dramatic releases of stored magnetic energy, emitting electromagnetic radiation from radio to hard X-rays or gamma rays. Large numbers of non-thermal ions and electrons are produced, but the origin of these high-energy particles is not understood. A promising theory is that particles are accelerated by the strong electric fields associated with reconnection of the magnetic fieldlines. This can be studied using a "test particle" approach, in which charged particle motion is calculated in electromagnetic fields representative of reconnection. A project is available to use test particle models to study the generation of high energy particles in solar flares - this will involve adapting existing computer codes, as well as some programming and analytical calculations.
Radio Recombination Lines with single dishesSupervisor: Prof Richard J Davis
We have used Parkes ZOA and HIPASS data at 1.4GHz to study Radio Recombination lines in our Galaxy. This is to study the ionised gas normally detected with Halpha emission to form a template for the Free-Free emission in our Galaxy: so important as a foreground to our CMB measurements, particularly for Planck. However this is not possible for low galactic latitudes due to the dust in our Galaxy. We thus turn to these radio frequencies where the dust is transparent.
We have very good data in the south with Parkes , but need to obtain good data in the north with the Lovell. We need to design a back end correlator system for JBO to enable us to observe the RRL's at JBO. The student will interact with others at JBO and JBCA to cost and design such a system.
HI intensity mapping for the detection of Baryon Acoustic OscillationsSupervisor: Dr. Clive Dickinson
Baryon Acoustic Oscillations (BAOs) are imprinted on matter throughout the Universe. They provide a key cosmological standard ruler, that can be used to measure the expansion of the Universe as a function of redshift and therefore can constrain dark energy models e.g. the equation of state. This is one of the key science drivers for the Square Kilometre Array (SKA) that will be fully operational during the next decade. However, a new technique called "HI intensity mapping" may allow them to be detected at radio wavelengths by mapping the redshifted 21cm HI line on large angular scales. Furthermore, this could be achievable within the next few years, providing complementary information and an independent test of the cosmological model.
We have proposed a single dish experiment, BINGO (BAOs using Integrated Neutral Gas Observations), that has the possibility of detecting BAOs (Battye et al. 2013). We are currently pursuing funding and site locations for the 40m dish required for BINGO. In the meantime, much preparation is required both on the instrumentation side, and on the analysis side. In particular, we need to make detailed simulations of BINGO data, taking into account the bright foregrounds and also instrumental systematic effects that could be problematic. These issues will be critical to the success of the experiment. We are also affiliated with other HI intensity mapping experiments including interferometric arrays that could be the focus of the project depending on progress with both experiments.
The student will become a member of the BINGO team and cosmology group at Manchester. Depending on your interest, and background, you will work with the BINGO team to develop simulation tools, component separation and analysis techniques, and may be involved in the design and testing of instrumentation for BINGO (e.g. testing of receivers, programming of digital backends etc.). An important aspect will be dealing with foreground contamination from our Galaxy and extragalactic radio sources.
Radio mapping of the sky using single dish dataSupervisor: Dr. Clive Dickinson
Sensitive mapping of extended diffuse emission, over a large region of sky, is notoriously difficult with single radio dishes. Firstly, total-power receivers are not stable over long time scales, resulting in large scale variations of power. Secondly, the atmosphere itself fluctuates in terms of the radiated power producing similarly large variations in power. This limits the maps that can be produced, which are traditionally limited in size and often filtered, leaving only compact sources. This is important for projects such as the One-Centimetre Receiver Array (OCRA), which is currently operated on the Torun 32-m telescope in Poland.
This project will investigate mapping techniques to allow single dishes to recover large-scale emission in the presence of large-scale correlated noise. One example is a Fourier-transform based technique by Emerson, Klein & Haslam (1979), but has only been exploited a few times in recent years. Simulations will be made to quantify how well this technique can be used for modern instruments, for a variety of targets and frequencies. Other algorithms (e.g. Maximum Entropy Method, or direct inversion) may be investigated. We will obtain test data from the OCRA instrument from Torun in Poland to test the algorithm and assess its performance.
Probing of the Magnetic Field in Star Forming Regions with SKA using CHSupervisor: Prof. Gary Fuller
Magnetic fields can play an important role in the formation of stars. This project will investigate the potential of SKA> observations of CH as a probe of the magnetic field in star forming regions. CH has two groups of transitions which can be observed with SKA. The lower frequency transitions, which are at a frequency around 700MHz, are potentially very good probes of the magnetic field. However there has been very little observational or modelling work done on these transitions. This project will investigate the nature of these CH transitions and through modelling, and potentially exploratory observations, how SKA1 and eventually SKA2 will be able to use these transitions to study the magnetic field in dense gas in star forming regions.
SiO Maser MoviesSupervisor: Dr. Malcolm Gray
SiO masers form in broken ring patterns around their host stars, which are mostly long-period variables of Mira and semi-regular variable type. These stars are pulsational variables, and the maser zone is disrupted by periodic shock waves that propagate outwards from the photosphere. The maser zone also coincides approximately with the condensation zone of alumina dust that helps convert pulsational motion into a steady outflow at larger radii. Hydrodynamic solutions for the atmosphere, coupled with maser pumping models, can be combined to provide a theoretical counterpart to a time-sequence of VLBI observations, improving our understanding of the establishment of mass-loss. It should be possible to make a movie of the motions of a number of maser objects at intervals of approximately one month over several pulsational periods.
Contaminating Weak Lensing Cosmology with Active Galactic NucleiSupervisors: Dr. Ian Harrison and Prof. Michael Brown
Measuring the weak lensing distortion of the shapes of millions of galaxies across the sky is an excellent way to learn about cosmological parameters and probe the different physical models of Dark Energy. Most weak lensing studies (such as the Dark Energy Survey) are conducted with optical telescopes, but recently new work has begun to focus on the prospect of weak lensing with radio telescopes such as e-MERLIN and the Square Kilometre Array (SKA). Doing weak lensing at radio wavelengths has a number of advantages but also a number of new challenges, one of which is the presence of different types of sources of the sample of galaxies used. The shapes of ordinary star-forming galaxies should be (relatively) easy to model with simple profiles with minimal error, but the shapes of Active Galactic Nuclei (AGN) in the radio are expected to be much more complex. The presence of AGN mistakenly included in the weak lensing sample can cause an error known as 'model bias' which directly affects the cosmological results. The aim of this MSc project will be to investigate how bad this model bias will be for different levels of AGN contamination and how it could be avoided.
The student will perform mostly computational work, simulating images of AGN and fitting simple models to their shapes. The student will gain knowledge in the general areas of cosmology, statistics and radio astronomy. The project has a well-defined outline and could easily lead to a published peer-reviewed journal article.
Gravitational lensingSupervisor: Dr. Neal Jackson
Gravitational lenses are systems in which a background object is multiply imaged by the action of the gravitational field of a foreground galaxy. Gravitational lensing is important because it allows us magnified views of distant objects in the Universe, and also because it allows us to investigate mass distributions in galaxies independent of their light emission. We are currently involved in a number of projects with major radio facilities (e-MERLIN and LOFAR) and planning for future surveys, including Euclid. Accordingly, there are a number of areas in which students could become involved:
- We have LOFAR observations of a cluster, A2626, with interesting radio structure and unusual radio arcs. This is likely to be an interesting exercise in cluster physics, but it is just possible that it may have something to do with lensing. The project will involve reduction and analysis of these LOFAR data (co-supervised with Prof. Ian Browne).
- We are currently conducting a survey, called LOBOS, to find long-baseline calibrators for the international baselines of the LOFAR array. This is a crucial project in making sure that these telescopes work properly and deliver observations. The project will involve helping with the LOBOS survey, and possibly extending this to providing calibration methods for other observations. (co-supervised by Dr. Amit Tagore).
- We are involved in a science working group of Euclid which is investigating the use of Euclid-discovered gravitational lenses for the study of galaxy evolution. The student will assist with the simulation of the scientific output from such a survey.
A first look at the Galactic magnetic field with the C-Band All-Sky Survey (C-BASS)Supervisor: Dr Paddy Leahy
The C-Band All Sky Survey is a major project to map the Galactic and extragalactic synchrotron emission, and particularly its polarization, across the whole sky. It will be used both to help understand the Galaxy's magnetic field, and to correct Cosmic Microwave Background polarization observations for the foreground synchrotron emission. We are using two telescopes, one in Owens Valley, California, and one in the Karoo desert, South Africa. We have now produced science quality maps of intensity and polarization with the Northern instrument, which allows us for the first time to study the synchrotron polarization across the Northern sky.This polarization depends on the Galactic magnetic field. The fractional polarization is fixed by the field tangling in the interstellar medium, while the field direction is given by the polarization angles. Residual Faraday Rotation at 5 GHz can be fixed by comparison with surveys at higher and lower frequencies such as WMAP and the DRAO Penticton survey, which gives the line-of-sight component of the magnetic field. The student will analyse all these maps to constrain models of the interstellar magnetic field.
All-sky map-making with Single Dish Radio TelescopesSupervisor: Dr Paddy Leahy
There are many projects in progress to map the radio sky at various different frequencies (from 300 MHz to 857 GHz) by scanning the sky with single dish telescopes. Examples include the WMAP and Planck cosmic microwave background satellites, C-BASS, and the GMIMS polarization survey which uses Penticton, Canada, and Parkes in Australia.
In all these surveys we wish to make a map of the sky, which comes down to finding the brightness of the radio emission (in several Stokes parameters) at each pixel in some convenient tiling of the celestial sphere. The problem is that the data is not collected by pointing at each pixel centre, but by scanning the telescope in some pattern with no particular relation to the sky pixelization. Since the telescope sees the sky convolved with its point-spread function (the "beam", as radio astronomers say), this gives full information about the sky provided that gaps between neighbouring measurements are smaller than half the beam width. The simplest way to treat such data is to bin each measurement into the nearest pixel, and this is what all current surveys do. But in many ways this is very sub-optimal and it would be better to interpolate the data onto the sky pixel grid. There are two problems to be solved: (i) computationally efficient interpolation onto the pixelised sphere (all standard interpolation routines work on a flat cartesian grid) and (ii) determination of the optimum interpolation function. The latter depends on the beam shape and also on the scientific purpose intended for the sky map. One example of the latter is to compensate for highly elliptial beams, such as some of those on WMAP and Planck, which otherwise make the sky maps difficult to interpret, especially in polarization.
This MSc project will produce and test an interpolation map-maker using the high-level IDL language, which will function as a prototype for an advanced map-maker for the Planck and C-BASS projects.
The chemistry of giant starsSupervisor: Dr. Iain McDonald, Prof. Albert Zijlstra
Twinkle twinkle, little stars. We don't wonder what you are, because we have measured your spectra. We can determine the abundance of various different elements in stars by measuring the strengths of the absorption lines in their spectra. This project involves measuring lines in the spectra of around 100 stars in a globular cluster, taken with the Magellan Telescope. These are very old stars which formed shortly after the Big Bang. Measuring their composition tells us about how these clusters formed, and about the very first stars that came before them. Previous experience with Linux would be helpful, but not required. Tailoring of the project to suit the strengths of individual student(s) may be possible, as we have a wider variety of globular cluster and dwarf galaxy data to analyse.
The Orbital Parameters of Radio Emitting X-ray TransientsSupervisors: Dr Tim O'Brien & Prof Ralph Spencer (Emeritus)
X-ray binaries are close binary star systems in which one star transfers matter to the other. The donor star is typically a main-sequence star (although some are more evolved) whilst the accretor is a more compact object, usually a neutron star or black hole. The release of gravitational potential energy in the accretion process causes the systems to be bright in the X-rays. Some of these systems show outbursts in which the X-ray brightness changes rapidly - these are known as X-ray binary transients. These systems also show radio emission, in many cases in the form of jets. The mechanism which drives these outbursts and variability is still not well understood. This project aims to explore the relationship between the radio/X-ray variability and the orbital parameters. For example, we might expect that binaries with circular orbits would have steadier accretion than those with eccentric orbits and hence might exhibit less variability. The project would involve collecting data on orbital periods etc, where known, and comparing these with known radio and X-ray properties. Observational data will be gathered largely from the published literature although archives, such as from the VLA, could also be mined where data are incomplete. Ways of appropriately characterising 'variability' would need to be investigated - so there are also signal processing aspects of the project.
Observation and modelling of nova explosionsSupervisor: Dr T.J. O'Brien
Novae are interacting binary stars in which a white dwarf accretes matter from a companion star. A thermonuclear explosion on the surface of the white dwarf ejects the matter, causing a significant brightening across the spectrum from radio waves to gamma rays. Our group and international collaborators are involved with monitoring nova outbursts using a range of telescopes and interpreting the observations in terms of hydrodynamic models of the explosion. A number of projects are possible in this area, including reduction and analysis of radio observations (including from e-MERLIN), hydrodynamic simulations of shocks and modelling of X-ray emission. Outstanding questions relate to the geometry of the ejecta and the ultimate fate of the white dwarf, in particular whether some of these systems eventually end as supernova explosions.
A superconducting parametric amplifier for the new generation of radio telescopesSupervisors: Prof Lucio Piccirillo, Dr Mark McCulloch, Dr Simon Melhuish
Parametric amplifiers are well known to have excellent low noise performances suitable for astronomical receivers. Very recently it has been proposed that the kinetic inductance of superconductors can be used as a non linear parameter to realise ultra low noise parametric amplifiers. These amplifiers have the potential to possess a large gain/bandwidth product and possibly even beat the quantum noise limit!
These amplifiers have also important applications in other fields like, for example, quantum computing.
The student will be involved in the theory of superconducting parametric amplifiers as well as in the design, realisation and testing of test amplifiers. During this work the student will learn radio-frequency design, cryogenic design and testing, low temperatures techniques (sub-K).
Direct detection of very high frequency gravitational wavesSupervisor: Prof. Lucio Piccirillo
Graviton to photon conversion is possible in the presence of a strong static magnetic field (inverse Gertsenshtein effect). The photon generated will be coherent with the original graviton. We are interested in exploring the theoretical and technical issues related to the direct detection of gravitons in the GHz to optical frequencies. The potential sources of such high frequency gravitons are at a moment very speculative: Kalutza-Klein 5D gravity and/or the inflationary period in the big bang. A prototype detector has been in operation for several months collecting useful data.
The student will be involved in the data analysis and simulations as well as in the continuation of the design studies for a more sensitive detector.
A miniature dilution refrigerator for astrophysical applicationsSupervisor: Prof. Lucio Piccirillo
Bolometers are the preferred detectors of astrophysical radiation in the mm/sub-mm and far infrared. When operating in low background, bolometers need to be cooled to extremely low temperatures 300 mK to 30 mK. Below 100 mK the preferred cooling technology is based on the dilution cooling of mixture of He-3/He-4. Our group is world leading in the development of miniature dilution systems that can be operated in small cryostats suitable for operations at the focal plane of telescopes.
The student will be heavily involved in the design, realisation and testing of a fully tiltable miniature dilution refrigerator.
Development of a novel passive correlator for the next generation of radio astronomy interferometers.Supervisor: Prof. Lucio Piccirillo
Diffraction of electromagnetic waves limits the angular resolution of radio telescopes. The larger the diameter of the telescope the better the angular resolution. Unfortunately, building larger telescope to achieve better and better resolution is very expensive: it scales roughly with the diameter to the power of 2.8. Radio interferometry allows us to achieve high resolution by combining the amplitude/phase of the electromagnetic waves coming from many small telescope. The combination is achieved by electronic correlators. Correlators are very complex electronic devices: the current limit to the number of antennas that can be correlated is of the order of few tens (the number of signals, or baselines, goes as the square of the number of antennas).
A novel passive correlator will be studied theoretically and especially experimentally. The idea to be tested consists in optically combining the amplitudes of the waves coming from each telescope in an optical "beam combiner". This system can potentially correlate hundreds of telescopes. The student will work with a team that will design, build and test a 3 x 3 quasi optical correlator working at 11 GHz. The prototype will be fielded at the Jodrell Bank Observatory from where observations of some strong radio sources will be performed.
Galactic Faraday Rotation with the Jansky Very Large ArraySupervisor: Dr. Anna Scaife
When the polarised radio emission from the ultra-relativistic electron population in high energy astrophysical objects passes through the magneto-ionised medium of our own Galaxy, the polarisation angle of such emission is rotated as a function of frequency - an effect known as Faraday rotation. By making observations over a range of different radio wavelengths this rotation can be used to infer the magnetic field strengths along the line of sight through the Galaxy between ourselves and the emitting object. This project will use data from the new P-band receivers on the Jansky Very Large Array (JVLA) telescope to develop a calibration strategy for measuring Faraday rotation from a bright polarised pulsar.
Radio Emission from Brightest Cluster Galaxies (BCGs) in Disturbed Galaxy ClustersSupervisor: Dr. Anna Scaife
It has been proposed that the brightest galaxies (BCGs) in clusters of galaxies that have undergone violent merger activity are less likely to produce radio emission than their counterparts in relaxed systems. This absence has been suggested to be due to more effective gas stripping, both during and following the merger activity. This project will use archival radio data to identify the fraction of BCGs which have detectable radio emission and to correlate the radio luminosity (as well as other characteristics) of these galaxies with the global properties of their host clusters, most specifically the entropy of the intra-cluster gas, in order to determine if relationships can be established which indicate the degree of disturbance necessary to prevent radio emission being produced.
Probing the Ionosphere with the KAIRA telescope.Supervisor: Dr. Anna Scaife
The Kilpisjärvi Atmospheric Imaging Receiver Array (KARIA) uses technology from the LOFAR array to form an independent radio telescope situated in Finnish Lapland (69°4'15''N 20°45'43''E). KAIRA monitors the Earth's ionosphere in a variety of different ways using novel techniques available due to the specialised underlying LOFAR design. One of these techniques uses the emission from pulsars - highly magnetized, rapidly rotating neutron stars that emit periodic radio bursts - to detect local temporal and spatial changes in the total electron content (TEC) of the ionosphere. To do this, KAIRA measures the amount of Faraday rotation caused by the ionosphere in the pulsar's polarized radio emission, which provides a linear measure of the line-of-sight electron density and magnetic field strength. Currently, KAIRA operates a pulsar mode only using its High Band Antennas (HBA; 120-180 MHz). In order to extend this experiment to the Low Band Antennas (LBA; 10-80 MHz) requires the individual sub-bands for the LBA to be sub-divided into narrower channels to maintain pulse coherence.
This project will design and implement a system to channelize individual sub-bands in the KAIRA-LBA using a poly-phase filter bank or other Fourier based method. This system will then be used to extend the KAIRA pulsar experiment to LBA frequencies. By including LBA frequencies, the accuracy with which Faraday rotation can be measured for these pulsars will improve significantly (Faraday rotation is function of wavelength-squared), allowing us to measure smaller changes in the ionospheric TEC content due to various space weather events. The student will have the opportunity to use KAIRA data directly to demonstrate their system.
Understanding the low frequency radio emission of the nearby spiral galaxy IC342Supervisors: Dr. Anna Scaife and Dr. David Mulcahy
At low radio frequencies (<300 MHz), the non-thermal radiation emitted from low frequency cosmic ray electrons (CREs) is strongly visible. These CREs suffer weaker synchrotron energy losses than higher energy CREs and are able to travel much further from their sites of origin. Consequently, taking data at low frequencies enables the observer to detect the very weak magnetic fields in the extended disks of galaxies where such CREs are produced. However, there is still a debate, based on early (historic) observations at low frequencies (< 100 MHz), over whether a flattening of the integrated radio spectrum can be seen - where the degree of flattening may be dependent on the inclination of the galaxy with respect to the observer. This flattening is proposed to be an effect caused by free-free absorption of the nonthermal emission by the presence of a clumpy ionised gas along the line of sight, with low electron density and temperature. Although no such gas has yet been observed in our Milky Way, determining the role of free-free absorption in the ISM is highly important and can only be investigated at low frequencies. To date, limited research has been performed at these frequencies due to the technical challenges imposed by the ionosphere; however, this is now starting to change thanks to the introduction of the next generation of radio telescopes, most notably the LOw Frequency ARray (LOFAR). In this project, the student will reduce a LOFAR HBA (110-170 MHz) observation of the nearby spiral galaxy, IC342. Comparing with higher frequencies images and through modelling, the student will investigate the propagation of the CREs in this galaxy, measure the strength of the magnetic field in the extended disk and finally determine if free-free absorption is occurring at these frequencies for IC342.
Finding the dark gas in the Milky Way.Supervisor: Dr. Rowan Smith and Prof. Gary Fuller
Despite the fact that the Milky Way is our home galaxy, there is still much that we do not know. In particular much of the gas that makes up our galaxy is "dark", i.e it cannot be observed using conventional methods. For example molecular hydrogen does not emit radiation at the typical temperatures found in the interstellar medium, instead its presence must be deduced from CO emission, but if the molecular gas does not have CO it cannot be observed. Alternatively if atomic hydrogen is optically thick then its true mass may be underestimated. This is especially true at the interface between cold molecular clouds, where stars like our sun form, and their hotter surroundings.
In this project we will perform mock observations of a recent high-resolution simulation of a Milky Way type galaxy. This will involve taking density, temperature and chemical abundance distributions from the numerical simulation and using a radiative transfer code to calculate the predicted emission. We will use the simulated emission maps to investigate where in the Galaxy "dark mass" might be hidden and what the implications might be for the formation of clouds of molecular gas. In particular we will make hydrogen absorption line profiles that can be compared to the THOR (the Hydrogen, OH and Recombination line) survey to test our models of how molecular clouds form. The comparison to this survey, being carried out by the Jansky Very Large Array, should allow the student to get a flavour of both theoretical and observational techniques. Some knowledge of programming would be beneficial for this project but as we will initially be using existing software and routines it is not absolutely essential.
Study fast radio transients with the Lovell TelescopeSupervisor: Dr. Ben Stappers
Radio Transients provide an opportunity to study some of the most extreme environments in the Universe. It is already well known that neutron stars can give off bursts of emission on timescales as short as nanoseconds, but bright radio bursts are also expected from Gamma-ray bursts, merging neutron stars or blackholes, or perhaps even evaporating black holes. The study of transients in the radio has recently undergone a rapid evolution with the building of new telescopes and significant improvements in computing capabilities. We have recently purchased hardware to undertake a survey for variable and transient radio emission with the Lovell Telescope. We will use this to piggy-back on nearly all observations with the Lovell, to get sufficient observing time to detect rare and interesting events. This project is to help develop the software required to perform these observations and to analyse the data. Once observations are possible the student will analyse the data to look for new, and known sources of transient radio emission with a view to detecting rare, and thus scientifically important events. This project requires someone with a good understanding of computing and software.
The Pulse Shape-Spin Down relationship for pulsars and the limits of pulsar timing precision Stappers and WeltevredeSupervisor: Dr. Ben Stappers
It has recently become clear that the apparently random variations in the pulse arrival times of pulsars are, at least in some cases, actually very deterministic. Moreover, they are strongly correlated to changes in the pulsed radio emission from the pulsar. This link, indicates that properties within the magnetosphere are changing globally and show that we need to consider the full electrodynamics of pulsar emission and spin in order to be able to understand this process. Moreover, this relationship shows that by measuring one property, say the pulsar shape changes, we can predict what the spin properties should be. This potentially provides a way to correct for the timing noise and thus make pulsars even better clocks than they already are. This is an extremely interesting area of research, as using pulsars as precise clocks for fundamental studies of gravity is an important aspect of the next generation radio telescopes like the SKA.
The LOW Frequency ARray, LOFAR, is the first of the next generation of radio telescopes to be built. It is located predominantly in the Netherlands but extends over much of Europe. unlike traditional radio telescopes that are based around large parabolic surfaces it uses small dipole-like antennae and combines them using sophisticated software and large computing power. Moreover it works below about 300 MHz, a frequency region previously very poorly studied. We have performed a survey of parts of the Northern sky to search for new radio pulsars. Pulsars are highly magnetised and rapidly rotating neutron stars and are some of the most extreme objects known. They are used for studies as varied as the behaviour of plasma in regions of high magnetic field to searching for gravitational waves. This project is to work on developing new and effective ways to find pulsars and to apply these techniques to our existing and new data sets to try and find new pulsars.
The 3D structure of the interstellar medium in the Galactic PlaneSupervisors: Dr. Alessio Traficante and Prof. Gary Fuller
The interstellar medium is mainly a mixture of hydrogen in its various states, atomic molecular and ionised, and dust associated with each of this phases. The dust in particular is a key tracer of the interstellar radiation fields and of star forming regions. We can observe the emission from dust in the infrared regime since it absorbs the incoming UV radiation from background and re-radiates it as infrared emission. However the emission we observe is a blend of emission arising from all the different atomic, molecular and/or ionized gas regions along the line of sight, each with its own properties. There is a method to decompose the integrated dust emission in its 3D structure along the line of sight, combining the infrared data with radio data that trace the hydrogen in its three phases separately, the so-called inversion method.
In this MSc project the student will apply the inversion method to the most recent infrared data of the Galactic Plane, observed with the Herschel satellite as part of the Hi-GAL survey of the Plane of our galaxy. This will be combined with radio data to trace the different gas phases. In particular, the student will explore the capabilities of the recent data from the Planck satellite to trace the emission arising from the molecular gas. The goal of this project is to map the 3D dust emission along a wide portion of the inner Galactic Plane and to understand the different properties of the dust as function of the Galactocentric position and different gas phases. The project will also explore the capabilities of the inversion approach in recovering such properties.
Gas content as the driver of observed galaxy propertiesSupervisors: Dr. Jeff Wagg (SKAO) and Dr. Rob Beswick
It has become clear in recent years that the total gas content of galaxies (atomic and molecular) governs many of their observed properties such as star-formation rate and stellar mass. Gas is ultimately the fuel for star-formation in galaxies, but most of what is known is based on small observed samples of molecular gas (traced by CO line emission) and atomic gas (traced by 21cm HI line emission). We are now entering an exciting era where new and upcoming submm through m-wavelength telescopes will vastly increase our knowledge of the gas content in galaxies.
We are undertaking a study with the APEX telescope in Chile, the IRAM 30-m telescope in Spain, and the Very Large Array in New Mexico, aimed at studying the CO and 21cm HI line emission in a large sample of nearby galaxies (see Bothwell et al. 2014, 2015). The goal is to understand how the gas content in these galaxies determines where they lie on the observed fundamental mass-metallicity relation. We have also just been awarded a large observing programme on the 12-m diameter Arizona Radio Observatory (ARO) to study CO line emission in a subset of our sample. The student will work on the existing CO line data from APEX, and will have the opportunity to travel to Arizona to be involved with the ARO observing. Assisting with some remote observing from Manchester would be expected thereafter.
A polarized view on the pulses of radio pulsarsSupervisor: Dr. Patrick Weltevrede
Radio pulsars are highly magnetised neutron stars which spin with periods of between a few millisecond and seconds. Each rotation the radio emission, which is beamed along the magnetic poles, sweeps across the Earth and can be detected by very sensitive radio telescopes as a regular sequence of pulses. The rotation of the neutron stars is extremely stable which makes them very accurate clocks allowing tests of the general theory of relativity. However, each of the individual pulses of the observed sequence vary greatly in shape, intensity and polarisation properties. These variations caused by largely unknown physical processes in the magnetosphere of these stars. In some cases these variations happen in a coordinated fashion, which are known as drifting subpulses. We have recently shown that this property seems to be endemic to the overall emission process of pulsars. In this project we want to compare the radio polarisation properties of a large sample of pulsars with their drifting subpulse properties to better determine the physics of the emission process. This process is still a mystery since the discovery of pulsars more than 40 year ago.