Astrophysics PhD Projects 2017
Magnetic reconnection and heating the solar corona
Supervisor: Prof Philippa Browning
Research in solar plasma physics is concerned with modelling the complex interactions of magnetic field with plasma in the solar atmosphere, in the context of the wealth of new space and ground-based observations of the Sun which is transforming our understanding of our nearest star. There are many synergies with the physics of magnetically-confined fusion plasmas, and there may be opportunities for PhD projects to explore both fusion and solar applications, with potential collaborations with CCFE (Culham Centre for Fusion Energy).
A major unsolved problem 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, but the details remain controversial. A strong candidate for an efficient energy dissipation mechanism is the process of magnetic reconnection - which also operates in solar flares, and in many other space and astrophysical plasmas.
PhD projects are available to model coronal heating through reconnection, both using numerical magnetohydrodynamic simulations and through semi-analytical modelling, based on the idea that the coronal field relaxes towards a minimum energy state. Current models of energy release in unstable twisted coronal loops will be extended to more complex configurations, investigating the multi-thread nature of coronal loops and interactions between different loops. One project will be to complement results from two-fluid simulations by developing a relaxation model appropriate for Hall magnetohydrodynamics.
The origin of solar flare energetic particles and their observational signatures
Supervisor: Prof Philippa Browning
Research in solar plasma physics is concerned with modelling the complex interactions of magnetic field with plasma in the solar atmosphere, in the context of the wealth of new space and ground-based observations of the Sun which is transforming our understanding of our nearest star. There are many synergies with the physics of magnetically-confined fusion plasmas, and there may be opportunities for PhD projects to explore both fusion and solar applications, with potential collaborations with CCFE Culham Centre for Fusion Energy).
Solar flares are dramatic releases of stored magnetic energy in the solar corona. They are manifestations of the fundamental plasma physics process “magnetic reconnection”, which occurs in many other space and astrophysical contexts as well as in fusion plasmas.
A challenging question is to understand how the magnetic energy is released and charged particles are accelerated to high energies in flares. We have been developing test particle models to show how particles can be accelerated in complex fields, both with fragmented current sheets and near magnetic null points. PhD projects are available to investigate particle acceleration and magnetic reconnection in solar flares, extending current models to incorporate the effect of the feedback of the accelerated charged particles on the electromagnetic fields, and investigating more realistic field configurations.
Students may use a new “reduced kinetics” approach to develop self-consistent models including energetic electrons and evolving magnetic fields. This work mainly relies on computer simulation, and may involve both the use of existing codes as well as code development.
An important aspect of this work is “forward modelling” of the observational signatures – the energetic particles may be detected both through hard X-ray and radio emission.
Towards precision mass measurements of cool exoplanets using microlensing
Supervisor: Dr Eamonn Kerins
Microlensing, which employs the principles of gravitational lensing, is the only current technique able to discover cool low-mass exoplanets that lie beyond a few AU from their host. Planet formation theories suggests that low mass planets in this region may not have migrated far since their formation. Therefore, understanding the demographics of these systems can allow us to directly test planet formation theories.
Microlensing surveys are now entering a new era of high precision mass measurement thanks to the increased deployment of wide-field high-cadence surveys (OGLE, MOA, KMTNet) which can now monitor hundreds of millions of bulge stars on timescales of minutes, but also because of the simultaneous use of space-based assets (Spitzer, Kepler, and possibly Euclid and WFIRST in the future). Simultaneous observations from space allow parallax microlensing effects to be detected, which are often crucial in breaking the three-way distance-mass-velocity dgeneracy in microlens modelling.
At Manchester we have developed the Manchester-Besancon MicroLensing Simulator (MaBuLS), the most advanced simulation of Galactic microlensing currently available. This computational project will involve extending the capability of MaBuLS to allow for parallax detection of microlensing so that it can use the full range of information to help provide population statistics on detected parallax events, including cool planetary but also black hole candidate lens systems. Previous experience with the use of Python will be beneficial.
Data mining the Galactic Centre: the near-infrared VVV survey
Supervisor: Dr. Eamonn Kerins
The Vista Variables in the Via Lactea (VVV) survey is a multi-year survey of the inner Galaxy at near-infrared wavelengths using VISTA, the World's largest infrared telescope. The VVV survey team is an international collaboration of European and Chilean astronomers. At Manchester our contribution to the project has been the development of a difference image analysis pipeline which can identify millions of variable objects from around 3 million images of around 100 million monitored stars. The key goals of the survey include:
the identification of "standard candle" variable populations such as RR Lyrae stars, which can be used to develop a 3D reconstruction of visible stars in the inner Galaxy;
the detection of rare gravitational microlensing events which allow us to determine the underlying mass distribution of the inner Galaxy;
the identification of stellar motions on the sky (proper motion) which allow us to measure the kinematical properties of the inner Galaxy.
This PhD project will involve working on one or more of the following areas:
The development of automated classification schemes for cataloguing different classes of variable and transient objects.
The development of a "citizen-science" front-end to allow public users to engage in classifying objects or finding specific classes of objects of interest.
Mapping the underlying distribution of RR Lyrae stars, Young Stellar Objects (YSOs), novae, and/or gravitational microlensing events, including a careful assessment of detection biases.
Detecting stellar proper motions and using this to constrain the kinematics of the inner Galaxy.
This project will involve a significant element of computation and software development in Python. Knowledge of Python is not a prerequisite, though a willingness to learn it is, as is a keen aptitude for programming.
Transmission spectroscopy of exoplanet atmospheres
Supervisor: Dr. Eamonn Kerins
We are entering a new era of exoplanet characterisation thanks to the large numbers of hot exoplanets (those orbiting close to their hosts) which have been routinely discovered by ground and space-based transit surveys such as SuperWASP, HAT and Kepler. Transmission spectroscopy is a highly successful technique for probing the atmospheres of hot exoplanets. This technique will be used more frequently as the samples of known nearby planets rapidly expands with the advent of surveys such as NGTS and the launch of the NASA TESS mission in 2017 and the ESA PLATO mission in 2025, both of which will detect relatively nearby exoplanets using the transit method.
Manchester has developed a transmission spectroscopy program in collaboration with colleagues at NARIT in Thailand. We have been very successful in gaining observing time on the ULTRASPEC instrument on the 2.4m Thai National Telescope (TNT) and other facilities. By observing the wavelength-dependent nature of the transit profiles we are able to constrain the atmospheric chemical composition of hot exoplanets down to the mass of Uranus.
A PhD project is available for a student to work as part of our transmission spectroscopy team. The student will be involved in the following areas:
selection of exoplanet targets for transmission spectroscopy observations
help with the preparation of observing proposals
data reduction and analysis of transit lightcurves using an existing pipeline developed at Manchester.
comparison of multi-wavelength transit curves with exoplanet atmospheric models.
Experience with Python programming will be beneficial.
Intensity mapping for future radio cosmology surveys
Supervisor(s): Prof. Clive Dickinson, Prof. Ian Browne (emeritus), Prof. Richard Battye
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 through Integrated Neutral Gas Observations), that has the possibility of detecting BAOs (Battye et al. 2013). BINGO is a collaboration between Manchester and UCL in the UK, U. Sao Paolo and INPE in Brazil, U. Montevideo in Uruguay and discussions with other partners are ongoing. It will make the most sensitive large-scale HI map of atomic hydrogen ever made, covering an area of >2000 sq. deg. The project has recently received funds from FAPESP in Brazil at the level of 3M US dollars and we are ready to begin phase 1 of the project, beginning late 2016, which involves site preparations (in Uruguay) and the construction of a complete single module. Once this has been shown to work to specification, we can then proceed to phase 2 (late-2017) where a full array of ~60 horns will be constructed along with the telescopes. The final survey is scheduled to begin around late-2018 and will last for 1-2 years at least.
The student will become a key member of the BINGO team and cosmology group at Manchester. You will work with the BINGO team to develop the instrument (testing, commissioning), and to analyse data from the prototype module and eventually from the full array. An interest in hands-on/practical radio astronomy is an advantage. Depending on your particular interest, you will also work the Manchester group in developing tools for simulations and data analysis including component separation, map-making, power spectrum analysis and cosmological analysis. An important aspect will be dealing with foreground contamination from our Galaxy and extragalactic radio sources and precise calibration, which is required to achieve the ultimate noise level. Much of the work will be in preparation for an intensity mapping survey with the SKA.
Constraining the physics of the early Universe with CMB polarisation
Supervisor: Prof Michael Brown
The Cosmic Microwave Background (CMB) is the most powerful cosmological probe. Measurements of the temperature anisotropies have established the current cosmological model, and are now culminating with the results from the Planck satellite. However, future measurements of the polarization of the CMB promises to open a unique window into physical processes that occurred in the very early Universe. In particular, a detection of the so-called B-mode polarization signal on large angular scales would effectively prove the theory of inflation and open a unique observational window onto physics at the Grand Unified Theory (GUT) energy scale. The JBCA cosmology group is involved in several future experiments designed to search for this early Universe signal (e.g. the ground-based Simons Array and Simons Observatory, and the proposed satellites CORE and LiteBIRD).
Since the sought-after signal is so subtle, the instrument design, observation strategy and data-analysis techniques all need to be optimised very carefully. Imperfections in the instrument, or in the way the telescope scans the sky, can lead to spurious signals in the data that can mimic the B-mode signature and ruin the analysis. The aim of this project is to optimise the instrument design, scan strategy, and data analysis techniques for these future experiments. The project will make use of analytic techniques and detailed computer simulations to investigate the impact of different design and scan-strategy choices on the ability of the telescopes to detect the inflation signal. This project would suit a student with interests in early Universe and fundamental physics and who has excellent analytic skills and experience in computer coding.
Beads on a String: The formation of stars by filamentary accretion
Supervisor: Dr Rowan Smith
Observations by the Herschel space telescope have shown that molecular clouds, the stellar nurseries of our galaxy, are threaded by long filaments of dense molecular gas in which stars form at regular intervals like beads on a string. Understanding this process has important implications for all of astronomy, as the number and masses of stars formed in a galaxy will affect it’s evolution when the massive stars explode in supernovae explosions. Moreover, as planets form around stars, it will also affect the types of planetary systems that can be formed.
This PhD project will use cutting edge numerical simulations of filamentary molecular clouds that include chemistry and magnetic fields to investigate to investigate such structures. We will investigate the formation of the filaments, and how they fragment into stars. In particular we will test how flows of mass along the filaments can lead to the formation of massive stars (greater than 8 solar masses) that will go supernovae when they die. A crucial part of the project will be to make critical comparison of the predictions of the above models with observational data in terms of observable quantities seen by instruments such as ALMA using post-process radiative transfer calculations. This means the student will learn to use both theoretical and observational techniques throughout their PhD thesis.
How do galaxies form stellar nurseries throughout cosmic time?
Supervisors: Dr Rowan Smith and Dr Scott Kay
Stars form in dense clouds of molecular gas in galaxies, but how the formation of these clouds and the stars within them depend on conditions within the galaxy is still unknown. In spiral galaxies, are clouds formed in the dense spiral arms more efficient at making stars, than in regions between the arms? Are molecular clouds the same in small irregular galaxies dominated by supernovae as in spiral galaxies? How does all this change in starburst galaxies where there is more energetic feedback from the forming stars? These questions are particularly important for galaxies at earlier cosmic times which are likely to be quite different to our current Milky Way.
In this project we will use ground-breaking high-resolution simulations of how molecular gas evolves in galaxies to answer these questions, and investigate how star formation may proceed in other galaxies beyond our Milky Way. We will vary quantities such as the galactic potential, gas surface density, stellar feedback and abundance of chemical coolants in the gas, to examine how molecular clouds may differ in other environments such as those found at earlier cosmic times. For this project, previous experience of programming and running large simulations would be beneficial, but is not absolutely necessary as the student will learn the necessary techniques throughout the project.
Search and study of the extreme neutron stars
Supervisor: Dr Rene Breton
Neutron stars are some of the most exotic objects populating our Universe: they have extreme densities and gravity, the largest known magnetic fields and the fastest observed rotations. For these reasons neutron stars are powerful tools to study fundamental physics. The two available PhD positions will be involved in the search and study of the most extreme neutron stars populating our Galaxy. They will focus on a particular type of neutron stars in compact binary systems called black widows and redbacks. They are nicknamed after deadly spiders because they contain an energetic radio pulsar which gradually destroys a low-mass companion. In recent years these ‘spiders’ have proved to harbour some of the most massive and fastest spinning neutron stars even found. Only a handful have been discovered and properly studied so far. The PhD candidates will be part of a team searching for new ‘spiders’ using a range of multi-wavelength observations. They will perform high-precision analysis of their optical and radio light curves in order to measure the neutron star properties (e.g. mass, rotation, magnetic field) as well as to study a range of phenomena such as radio eclipses and the impact of relativistic heating on a nearby low-mass star.
The eyes of SPHERE
Supervisor: Prof. Albert Zijlstra
Stars like the Sun, at the end of their lives, eject much of their mass back into space. This is the main source of dust and carbon, building blocks of planets and life: these stars drive hte evolution of the Universe. The ejected shells are briefly visible as a planetary nebula: the fantastic structures show that the ejection is a complex process. It is not thought that much of the shaping comes from interacting binary stars, but direct observations of such interaction have been too difficult. A new instrument, SPHERE, has recently been developed for the ESO 8-meter Very Large Telescope. With its extreme adaptive optics system, it provides the sharpest images ever obtained, with resolutions down to 15 milli-arcsec. Originally developed to image extra-solar planets, it has been shown to also be able to image these interacting binaries. This project will analyze the first such data taken of a number of dying stars, to see the onset of the interactions. The student will spend up to half the time at the Observatoire de Nice to work with dr. Lagadec (this long-term attachment is available to STFC-funded students). The project will train the student in the use of next generation of high angular resolution instrument, such as developed for the European 39-m telescope, and in the use of 3D radiative transfer codes, as well produce unique data on the death of stars.
MeerTRAP - Searching for Pulsars with MeerKAT
Suparvisor: Prof Ben Stappers
MeerTRAP is a European Research Council funded project to use the extremely sensitive MeerKAT telescope to search for pulsars and fast transients. This PhD project will enable the applicant to become a member of this team and work with the team on the development of the pulsar search pipeline and use it to find new pulsars and then undertake detailed studies of the sources that are discovered.
Radio pulsars are some of the most extreme objects in the known Universe. They have masses of about 1.4 times that of our Sun, radii of about 10 km and they spin at up to 700 times per second. They are exceptionally stable clocks that provide us with excellent tools for studying matter at high densities, ultra-strong magnetic fields and even for studying gravity and spacetime itself. MeerTRAP will use commensal observing time, piggybacking on the large MeerKAT Legacy Science projects, to find new pulsars. This approach means that there will be many
repeat visits to the same area of sky on a range of different timescales. This provides us with excellent sensitivity to sources that vary for any particular reason, either because they are intrinsically variable, members of relativistic binary systems or transitioning millisecond pulsars. The applicant would become a member of a team including 3 PDRAs and 3 PhD students plus support staff and would join an international collaboration. They would be involved in developing the capabilities for searching the 400 beams that will be generated for new pulsars across the sky. They will be involved in the discovery of new pulsars and their characterisation across the electromagnetic spectrum, including using our access to the MeerLICHT telescope. The successful applicant would need to have a good background in astrophysics or physics and computing.
MeerTRAP - Searching for Fast Radio Transients with MeerKAT
Supervisor: Prof Ben Stappers
MeerTRAP is a European Research Council funded project to use the extremely sensitive MeerKAT telescope to search for pulsars and fast transients. This PhD project will enable the applicant to become a member of this team and work with the team on the development of the fast radio transient search pipeline and use it to find new transients and then undertake detailed studies of the sources that are discovered.
MeerTRAP will use commensal observing time, piggybacking on the large MeerKAT Legacy Science projects, to find new fast radio transients. Using a combination of a large number of coherent beams and the incoherent summation of all the dishes the survey will probe a range of sensitivities and timescales that will reveal larger populations of known transients like fast radio bursts and classes of transients not yet known. It is expected, for example, that up to 30-40 new fast radio bursts will be discovered every year. These will be studied in detail using our transient buffers, including forming images to accurately localise them. We will also carry out multi-wavelength follow up and this will include using our access to the MeerLICHT telescope which is slaved to the positions looked at with MeerKAT. The applicant would be a member of a team including 3 PDRAs and 3 PhD students plus support staff and would join an international collaboration. They would be involved in developing the capabilities for searching for transients in all operational modes of the telescope. They will also be involved in the discovery of new transients and their characterisation across the electromagnetic spectrum and also the study of their host locations and potentially using them as cosmological probes. The successful applicant would need to have a good background in astrophysics or physics and computing.
Understanding Blazar Jets - The OVRO 40-m Blazar Monitoring Program
Supervisor: Prof Keith Grainge
Active Galactic Nuclei (AGN) are powered by accretion onto rotating super-massive black holes which create relativistic jets along the spin axis, though the detailed mechanism of this process still remains elusive. In the cases where the jets are aligned at a small angle to the line of sight, relativistic beaming dramatically boosts the apparent luminosity and variability; these objects are collectively known as “blazars.” One avenue for progressing our understanding of jet production is provided by the Fermi Gamma-ray Space Telescope, which continuously monitors all gamma-ray bright blazars, allowing an unprecedented opportunity for the systematic study of blazar jets. The exact location of the gamma-ray emission region and its proximity to the central black hole remain subjects of debate, with two main competing classes of models for the GeV emission region. Testing these models requires a multi-wavelength approach, combining the Fermi observations with supporting radio observations to search for correlations in the light curves at different frequencies.
This project is centred around the radio monitoring of 1500 blazars with the 40-m telescope at the Owens Valley Radio Observatory (OVRO, California) and then producing a joint analysis with Fermi data. The 40-m now has 8 years of intensity observations, which now offers a very powerful data set for correlation studies. In addition, a new polarisation sensitive receiver is currently being commissioned on the 40-m, and so a novel set of additional information will shortly be available for incorporation into the analysis. This project offers the possibility for the student to take a Long Term Attachment for 3+ months to Caltech, Pasadena, in order to visit the OVRO site, to contribute to the 40-m observing, and to learn about the low-level data reduction. The project will be co-supervised by the lead of the Caltech team, Prof Tony Readhead.
Design and construction of a continuous miniature dilution refrigerator for POLARBEAR2 and SIMONS array
Supervisor: Prof. Lucio Piccirillo
POLARBEAR and SIMONS array are two CMB polarization experiments dedicated to the detection of the B-modes sited at high altitude at the Atacama desert in Chile. The University of Manchester, ATT team, is involved in the design and construction of the sub-K refrigerators that are at the heart of the receivers. The sub-K refrigerators will cool the bolometric arrays to base temperatures as low as 100 mK where the bolometers reach maximum sensitivity.
The students will be involved in all the phases of the design, construction and testing of the refrigerators. It is also expected that he/she will participate in the observing campaigns.
Design and development of very Low Noise Amplifiers with direct electron channel cooling.
Supervisor: Prof. Lucio Piccirillo
A new of Low Noise Amplifiers for Astronomy and Astrophysics will be designed, realized and tested. These new amplifiers will potentially be integrated in the future generation of astronomical instrumentation. This projects involves collaboration with Chalmers University of Technology in Sweden.
Design and realization of a wide-band sub quantum noise parametric amplifier (paramp) based on the non linear kinetic inductance property of superconductors
Supervisor: Prof. Lucio Piccirillo
This project involves the design and development of an ultra low noise parametric amplifier for future radio astronomy observatories. It will consist of a superconducting thin film exhibiting highly non-linear kinetic inductance. When pumped with an external RF signal it will be driven in a state of parametric amplification with potential sub-quantum noise characteristics. This project involves a collaboration with Oxford University, Grenoble and Chalmers.
Strong gravitational lens research at JBCA
Supervisor: Dr Neal Jackson
Strong lens systems, where a background galaxy or quasar is multiply imaged by the gravitational field of a foreground galaxy, are important for several reasons. First, they tell us about the mass distribution of the foreground object independent of the light it emits. Second, the lensing also magnifies, providing us with views of sources otherwise too faint to see. Third, some lenses are useful for cosmology. The group currently includes a postdoc who specialises in lens modelling and interpretation, and students involved mainly in observations. We have a number of programs in which new students may be able to get involved:
- An e-MERLIN Legacy Programme aims to look at a
number of known lens systems in order to study one of their
images, in each case that in the centre of the system which gives
information about the central part of the gravitational potential
of the lens, close to the central black hole. Due to recent
upgrades this programme should be able to start in 2017.
- We are studying radio-quiet quasars using radio telescopes and exploiting lensing magnification, which allows us to measure structures and properties of objects which (as their name implies!) are otherwise difficult to study.
- We are involved in a number of development programmes aimed at lens surveys in future telescopes such as Euclid, and existing novel radio telescopes such as LOFAR. In the case of LOFAR, an interferometer based in the Netherlands, this includes technical work on calibration of high-resolution images.
Computational Models of Astrophysical Masers
Supervisor: Dr Malcolm Gray
New interferometric instruments such as ALMA have enabled us to produce detailed images of masers in the 100-GHz to 1-THz region for the first time. Single-dish instruments, such as the airborne SOFIA, are opening up an observing window at frequencies above 1-THz. We need computational models of methanol, ammonia, formaldehyde and water masers in star-forming regions, evolved stars and external galaxies to test our understanding of these new observations. The project involves two types of modelling: The first type is parameter-space searching, where the non-LTE radiativ e transfer problem is solved in a fairly straightforward model many times over a wide range of physical conditions. This allows us to identify the optimum conditions for amplification in the observed maser lines, and to select transitions for new observations by SOFIA. The second type of model involves more sophisticated simulation of specific sources, for example the red supergiant star VY CMa, which has now been imaged by ALMA in the 321, 325 and 658GHz water maser lines. Since the number of water maser lines comfortably exceeds the number of formal free parameters in the computer models, it may be possible to attempt the inverse problem for masers, where physical conditions are inferred from brightness ratios at the highest spatial resolutions, corresponding to co-propagation of masers at different frequencies.
The Origin of Maser Flares
Supervisor: Dr Malcolm Gray
Astrophysical masers are known to vary on timescales from minutes to decades, depending greatly on source type and molecular species. Most of this variability is of fairly low amplitude and/or slow. However, there are, in addition, flaring events, where the maser flux density, as measured by a single-dish radio telescope, changes by orders of magnitude on a timescale of days or even less. Flares may be periodic, aperiodic or pseudo-periodic, and there is at least one example where flares in two different maser species, water and methanol, are coupled in a periodic, mutually exclusive flaring pattern.
A new 3D maser code will be applied to the flaring problem, to generate synthetic light curves that can be compared with observations. Likely scenarios that can be tested with the code are rotation of irregular objects, line-of-sight overlap of masing clouds, clusters of objects orbiting in discs, and maser sources pumped by periodic episodes of infra-red irradiation.
Radiative Transfer of Radiation with OAM
Supervisor: Dr Malcolm Gray
Radiation with orbital angular momentum (OAM), as opposed to the spin angular momentum (SAM) associated with polarization, may be routinely generated in the laboratory. Methods mostly include the insertion of a special phase-modifying component into a laser beam. Radiation with OAM has a number of unusual features: the instantaneous Poynting vector is not parallel to the direction of propagation, about which it traces a helical path; there is a component of the electric field in the direction of propagation and an infinite number of quanta of OAM may (in principle) be applied.
Radiation with OAM has yet to be detected from an astrophysical source, though there is strong evidence that it is added to astrophysical signals by atmospheric turbulence.
The project is to consider the transfer of radiation with OAM, and, in particular, its generation by (i) turbulent velocity fields, where the local gradient of the refractive index may be very high, (ii) regions of organized but inhomogeneous magnetic fields and (iii) by locally intense gravitational fields.
Very High-Frequency Resolution Observations of Masers
Supervisor: Dr Malcolm Gray
A new generation of radio interferometers, including e-MERLIN at Jodrell Bank, and the JVLA, has correlators that are highly flexible in the arrangement of the frequency channels, of which there are typically tens to hundreds of thousands. These instruments have the capability to observe spectral lines with a resolution as fine as 1Hz, or slightly better. In the case of maser lines, such resolution offers the possibility of investigating some fundamental properties of astrophysical maser radiation. Do astrophysical masers have radiation statistics that depart from the Gaussian form that holds for thermal radiation, for example?
In the case of highly-evolved giant stars, the high resolution may be used to detect correlated frequency shifts between a number of separate maser features, enabling us to detect the passage of acoustic and MHD waves through the circumstellar envelope: a form of circumstellar seismology that has not been previously attempted. e-MERLIN time has already been awarded to obtain the first data for this project, and observations will commence when the recirculation system in the correlator has been completed and tested.
Magnetic fields around Radio Galaxies
Supervisor: Dr Paddy Leahy and Dr Anna Scaife
The polarization of radio emission from distant radio sources is affected by Faraday rotation, through which we can trace the magnetised intergalactic plasma through which the radio waves travel. Faraday rotation maps of individual radio galaxies probe the magnetic field pattern in the gas surrounding the radio lobes, typically the atmosphere of a group or cluster of galaxies. Only a few dozen objects have been mapped so far in detail but the results are already puzzling. A number of objects show a strong "banding" pattern (e.g. Guidetti et al 2011) which is difficult to explain in terms of current models for the magnetic fields in clusters. It is not even clear whether this structure is induced by the expansion of the radio lobe bubbles, or is tracing general magnetic field in the cluster. ASKAP, the Australian Square Kilometre Array Pathfinder, will make Faraday rotation maps of most of the sky over the next few years (the POSSUM project). ASKAP will be fully operational with 30 antennas in 2018, and Early Science observations with 12 antennas, giving reduced resolution but a wider frequency range, already started in September 2016. POSSUM will measure Faraday rotation in 3 million sources. While most of these will be unresolved, thousands will be large enough to map. Even the Early Science phase will allow RM mapping of around a dozen nearby and giant radio galaxies. In this project the student will search such for objects in the Early Science data and in the first results from the main POSSUM survey, and analyse the Faraday data to help understand the magnetic field structure around them. During Early science there will be intensive work to optimise ASKAP operation and to perfect its calibration for polarization, and the student will be involved in this work, likely involving travel to the Alan Pawsey data centre in Perth, Australia, where the main ASKAP pipeline will run.
