PhD projects 2012

Our current understanding of the Universe favours a scenario where the late-time expansion rate is increasing, a measurement that has just led to the 2011 Nobel Prize in Physics. This so-called cosmic acceleration is most easily explained with the addition of a cosmological constant, Lambda, to Einstein's field equations in General Relativity. More generally, the acceleration can be modelled as due to a fluid with negative pressure, known as Dark Energy. An alternative possibility is that General Relativity is wrong on large scales and that the Ricci curvature scalar, R, must be replaced with a more complex function, F(R). Recent work (for example by Appelby & Battye 2007) has shown that F(R) models can be devised that reproduce the large-scale acceleration while also satisfying existing observational constraints (recovering GR) on small scales.

One of the key goals in cosmology over the next decade will be to use massive surveys for galaxies and clusters of galaxies (such as those to be performed with Euclid, e-Rosita and the Square Kilometre Array) to discriminate between Dark Energy and modified gravity models through various measurments of the growth of large-scale structure. Many of these tests will be on scales where structure formation cannot be described accurately by linear theory and non-linear corrections must be accounted for. Currently the most accurate method for modelling non-linear structure formation is cosmological N-body simulation, however the development of such simulations with modified gravity is as-yet an underdeveloped area.

This PhD project offers an exciting opportunity for a student to work on the development of such N-body simulations in conjunction with Richard Battye (an expert in theoretical cosmology) and Scott Kay (an expert in N-body simulations). The main aims will be twofold. Firstly it will be to incorporate and test plausible F(R) models against more straightforward Dark Energy models, by comparing statistical properties of the matter distribution such as the halo mass function and power spectrum. The second task will be to use these models to make observational predictions for the constraining power of future surveys such as with Euclid and the SKA, and thus their ability to discriminate between the different underlying mechanisms for generating cosmic acceleration.

Magnetic fields affect almost every astrophysical phenomenon, from the Earth’s aurora to the tenuous ultra-hot gas filling the potential wells of clusters of galaxies. The search for magnetic fields in truly intergalactic space is one of the hottest topics in cosmology, and a key project for the planned Square Kilometre Array (SKA).

We do not yet understand where magnetic fields on galactic and larger scales come from. Magnetic fields can be generated in stellar dynamos, and spread through the universe along with other stellar products like heavy elements via stellar winds and supernova explosions; alternatively seed fields can be generated in the early universe in some models, which can then be amplified by galaxy-scale dynamos and spread to larger scale by galaxy-scale winds powered by supernovae or active nuclei. More speculative cosmological models can produce detectable intergalactic fields directly. These galactic and cosmological-scale fields can be traced by radio telescopes in two ways: first, synchrotron radiation depends on the field strength and its polarization perpendicular to the projected field in the source; second, Faraday rotation of the polarization is caused by magnetic fields between the source and observer. We are involved in several new surveys to study these effects and a PhD place is available to participate in the observations and in their interpretation.

The new data comprises: (i) All-sky maps of the synchrotron polarization from our Galaxy at frequencies at 21 cm (the GMIMS survey at Penticton in Canada), 6 cm (C-BASS at Owens Valley California and the Karoo, South Africa), and observations with the WMAP and Planck satellites (13 to 3 mm). (ii) The Galactic ALFA continuum Transit Survey, a map of nearly half the sky at 21 cm wavelength with the giant Arecibo radio telescope. This will map the Galactic radiation in much more detail than GMIMS, and in addition ~100,000 distant radio sources which can be used to map Faraday rotation in the Galaxy’s field and also to trace any interstellar magnetic field. (iii) The POSSUM survey with the Australian SKA Precursor (ASKAP), currently under construction. ASKAP will be by far the most powerful radio survey telescope until SKA itself is built in the 2020s. POSSUM will map the 21-cm polarization in ~ 3 million distant galaxies, allowing similar science to GALFACTS but in the southern sky, but also will have the angular resolution to resolve the magnetic patterns in thousands of nearby galaxies and in the giant lobes of distant radio galaxies. All the 21-cm surveys (GMIMS, GALFACTS and POSSUM) have broad-band multichannel receivers allowing measurement of Faraday rotation.

The PhD student will be able to participate in the final reduction of the GALFACTS data (observations will be completed in Spring 2012) and in the early observations for POSSUM, expected to start at the end of 2013. There will be opportunities to travel to Australia and South Africa to participate in the POSSUM and C-BASS observations, and to the Very Large Array in New Mexico for follow-up observations of selected POSSUM targets.

Spatial resolution and sensitivity increases will allow new facilities (e.g.the Atacama Large Millimetre Array, ALMA) to study the local interstellar medium (ISM) at spatial resolutions never obtained before. These observations will allow us to study the structure of molecular clouds and initial stages of star formation in unprecedented detail, for example.

This project will build the next-generation in astrochemical models, which can deal with the stochastic nature of physical and chemical processes on small spatial scales, and apply it statistically to current (lower) resolution observations.

While mostly theoretical and computational, the project will have an observational component and the student will learn all the skills required to be a successful astrochemist.

Two processes dominate the appearance of our universe: star-formation and accretion. Star-formation (SF) is fundamental to the formation and evolution of galaxies whilst accretion provides a major power source in the universe, dominating the emission from distant quasars as well as from nearby X-ray binary systems. Radio observations provide by far the best single diagnostic of these two processes, providing a direct view of star-formation even in dusty environments and allowing detection of AGN and measurement of their accretion rate at bolometric luminosities far below anything detectable at higher energies.

During 2010/11 a new radio interferometer, e-MERLIN, will be commissioned and begin full operations at Jodrell Bank Observatory. Due to its extreme sensitivity (20x greater than current instruments) and high angular resolution e-MERLIN is, and will remain for the foreseeable future, the best radio facility in the world for the study of SF and accretion. As part of an ambitious legacy programme, JBCA is leading a large legacy survey of nearby galaxies. Over the next few years the LeMMINGs project, which was recently awarded 810 hours of e-MERLIN time, will survey and image around 300 galaxies in the nearby Universe, allowing many individual galaxies to be studied on sub-parsec scales with unprecedented sensitivities. The three primary drivers for this project are:

To measure levels of SF activity in galaxies of all morphological, luminosity and spectral population mix. These measurements, and in particular the resulting systematic and unbiased census of individual SF products (RSNe, SNR, HII regions and alike), will be used as a direct extinction-free tracer of SF, and hence be used to help calibrate commonly used SFR indicators such as IR and H-alpha.

-A complete census of AGN activity and jet structures in galaxies of all optical types, including LINERs and absorption line galaxies as well as broad line AGN, which will be cross-correlated against levels of ongoing SF.

-A serendipitous parsec-scale imaging survey of the cold ISM using its HI absorption and maser emission. This survey will constrain the content and composition of cold gas present in the immediate nuclear region of galaxies as well as its kinematics. Both of which are basically unknown on these size scales and can be addressed with e-MERLIN well before ALMA or the SKA are fully operational.

We are searching for new PhD students to work in any of the three of the primary themes of this project. In particular PhD students in this area will be heavily involved in the observations and exploitation of the first data to come from this project, and from e-MERLIN itself.

The student's main roles will be to:

-Lead the science exploitation of the very first e-MERLIN images of nearby galaxies. With the aim to study the key star-formation process in individual galaxies.

-Aid the commissioning of e-MERLIN as a whole, and in particular data processing procedures and the development of pipelines.

-Play a key role in the planning and execution of observations for the LeMMINGs project The LeMMINGs project will span ~2.5 years, starting in early 2012 and hence the PhD student will be involved in the project at all stages.

-Develop pipelines for e-MERLIN data, specifically focussed upon LeMMINGs data.

-Play a central role in the science exploitation of these new data.

-Plan and execute a wide-range of multi-wavelength (x-ray through to radio) follow-up observations using ground and space-based telescopes.

More details on the LeMMINGs project can be found at http://www.jb.man.ac.uk/~rbeswick/LeMMINGS

PhD candidates interested in this project are encouraged to contact me via email (Robert.Beswick@manchester.ac.uk) or drop by my office (Alan Turing Building, Rm3.209) to further discuss potential projects.

Gravitational lenses are objects in which light from a background object, such as a distant galaxy or quasar, is bent by the action of the gravitational field of a foreground object, forming rings and multiple images. They are important because they allow us to probe mass distributions of galaxies at large distances, independent of their matter content. This is important because it can allow the direct study of dark matter in the lens galaxies. We are undertaking a number of observational programmes in the area which can form the basis for a PhD project.

The main project is a large e-MERLIN Legacy programme, which is expected to start in 2012. One aim of this programme is to study the central regions of galaxies, which contain a central stellar cusp together with a massive black hole. In theory, if the background source of a lens system is radio-loud, we should see a faint image of the background source close to the centre of the lens, corresponding to light that has passed close to the centre and which carries information about the central gravitational potential well. The image is likely to be very faint, and only now do we have the sensitivity to routinely detect it and hence study the centres of galaxies at cosmologically interesting redshifts.

In addition, the Legacy programme aims to map the lenses in more detail, to reveal new structure within the known images. Analysis of these images can reveal further details of the mass distribution in the lens. We are also attempting to observe further lens systems with the EVLA which have not been previously detected in the radio, again in order to investigate how the dark matter is distributed in these galaxies.

Finally, we are involved in the LOFAR project, a large low-frequency telescope in the Netherlands. It is likely that large-scale surveys will be started with this telescope in the next few years, and one of the programmes that can be attempted with these surveys is the search for new gravitational lens systems.

Our knowledge of the possible architectures of planetary systems is making rapid advances thanks to the discovery of more than 600 extra-solar planets (exoplanets) over the past two decades. NASA's Kepler space mission has recently added another 1200 candidate planets to that list. However, the vast majority of these systems are both massive and close to their host star. Planet formation theories predict a dominant population of lower mass planets at larger stellar host separation, beyond the so-called snow-line. Some theories also predict the existence of a population of planets which have been ejected from their host system, a population dubbed free-floating planets. Sensitivity to cold exoplanets and free-floating planets is critical for informing planet formation theories and to complete our understanding of exoplanetary architectures. Gravitational microlensing, involving the temporary deflection of background star-light by the gravitational field of a foreground planetary system, is currently the only available exoplanet detection method able to survey the cold and free-floating exoplanet regimes down to Earth masses.

JBCA is a world-leader in the use of microlensing to detect exoplanets and we are involved in a number of ongoing and planned surveys for exoplanets. We are also designing space-based microlensing surveys, to be undertaken with the ESA Euclid or NASA WFIRST missions, which will probe exoplanets from the habitable zone out to the free-floating regime. The surveys are being designed using a state-of-the-art microlensing simulation developed at JBCA.

PhD projects are available for a student to join the JBCA Exoplanets Group working in the following areas:

• The development of GPU and volunteer computing (BOINC) methods for rapid modeling of signals from exoplanetary microlensing events. This development will use Python and C++ programming languages. Previous experience of C++ is desirable for students working on this project but the student need not have previous experience of Python.

• The development of automated data reduction pipelines for use by the MiNDSTEp and AST3 surveys. The MiNDSTEp survey uses a 1.5m optical telescope located at La Silla, at the edge of the Atacama desert. The Chinese-led AST3 project involves three automated wide-field Schmidt Telescopes based at Dome A in Antarctica. From 2013 AST3 is expected to conduct round-the-clock surveys for exoplanets.

• The developement of end-to-end simulations of exoplanetary microlensing surveys by wide-field optical/infrared space telescopes such as ESA's Euclid and NASA's WFIRST missions. JBCA is leading the survey design development within the Exoplanets Working Group for Euclid and Kerins is also an exoplanet science consultant for the NASA WFIRST Science Definition Team.

Students on any of these projects are also welcome to contribute to MiNDSTEp exoplanet observing runs at La Silla, Chile. For further enquiries email exoplanets@jb.man.ac.uk.

The Lovell Telescope was built in 1957 and is now largely used for Pulsar Astronomy where the Radio Frequency Interference (RFI) is mitigated by the pulse nature of the astronomy and also for MERLIN and VLBI where the use of interferometers mitigates the Interference. The presence of RFI and the great cost of very large spectrometers and the pursuance of pulars and interferometer observations has sadly left the Lovell telescope devoid of a state of the art spectral line system even though we have a four beam two polarisation receiver for the telescope. Two things have now changed this situation: very large spectrometers are now feasible for tens of Ks rather than millions of Ks using the latest hardware and firmware enabling mitigation of RFI which can test such ideas for the SKA and also giving excellent spectral resolution for the astronomy and secondly, there is now great interest in using the telescope for spectral lines particularly around the HI neutral Hydrogen frequency of 1420 MHz. This is of interest for two reasons:

1. Baryonic Acoustic Oscillations (BAO) produce the Large Scale Structure (LSS) which is expected to trace the dark matter distribution. A new approach is to measure the LSS using a relatively moderate telescope like the Lovell Telescope to measure the integrated HI on scales of ~arcmin to several degrees.
2. Radio recombination lines (RRLs) can measure the hot ionised medium which gives free-free emission. We use this in regions where the densities are high on the Galactic Plane and dust absorbs the red light associated with Halpha emission normally used to measure the free-free emission.

The most important tool for studying the Universe on the largest scales, has been detailed measurements of the Cosmic Microwave Background (CMB) radiation. The success of future CMB experiments lies in the understanding and removal of foreground emission from our own Galaxy. RRLs are required for foreground subtraction of the Cosmic Microwave Background. This is particularly timely in these days of Planck. The early CMB experiments were not sufficiently sensitive to be troubled by the foregrounds. With each generation of instrument the foregrounds become more and more of a problem. We need to separate the synchrotron and free-free anomalous dust and vibrational dust to enable these sensitive observation of the CMB.

We have mapped the radio recombination lines around 21cm with the Parkes radio telescope. We use 166,167 168 alpha all in the 64 MHz bandwidth of 1420MHz of HI. We have made maps of the diffuse emission from these RRLs. This has been achieved in the latitude range of +/- 4 degrees and with all the longitudes viewable from Parkes. We now wish to complete this in the North with the Lovell telescope. This will then enable subtraction of the free-free emission all along the galactic plane where the dust obscuration is such a problem.

With modern correlators and software processing it is possible to mitigate for RFI for these spectral lines. Developments in astronomy have led us to wish to develop spectral line work for the Lovell telescope for which it was originally designed.

The telescope itself was largely upgraded in 2001 and works extremely well at L-Band and C-Band. Due to the radio environment it has been left with rather poor instrumentation for spectral lines with pulsars and interferometry dominating the observing time. Thus new developments in technology and astronomy now make it extremely desirable and indeed technically possible to build a sophisticated spectral line back-end for this iconic telescope.

It emerges that a suitable correlator/spectrometer does not exist for the L-band multibeam. We have 8 signals to process: 4 beams in 2 polarisation. We propose a similar bandwidth of 64 MHz with a channel spacing of 12kHz. Thus we need 5000 channels for each signal making a total of 40,000 channels. This is sufficient resolution to measure the RRLs noted above and with so many channels it should be possible to remove the RFI.

In discussions it emerges that we could use the Roach Ibob Caspar system, which has been developed for SKA and for CBASS albeit with a much smaller number of channels. The software is more developed and easier to program than other RTSG systems. This will give the Lovell telescope a state of the art spectral system. This could be very useful to SKA as a pathfinder of this novel technology. Also with these enormous number of frequency channels we can mitigate RFI which of course is very important for the JBO site. This fits in very well with the guidelines for the Paul Instrument fund. These RRL lines are very narrow and we should be able to extract them with such a sophisticated system.

The PhD project would involve development of the spectrometer system for the Lovell. This will either involve our own system, a National Instruments system from the MSc course or even use of the pulsar backend system depending on funding. The student would then go on to survey both on and off the galactic plane for RRLs. Further studies may involve more wide band observations for redshifted hydrogen where mitigation of interference would be developed towards HI detections.

I have established the condition of the L-Band multi beam and its LO and 8 downverters. Also the filters and further amplifiers have been rescued. Help from JBCA, hopefully funded as I say, with getting the Caspar output into a computer at JBO for data acquisition. There are 8 signal paths down the telescope unless they come down digitally and are multiplexed

The study and the accurate knowledge of optics characterisation in the radio to sub-millimetre spectral range (10 GHz to few THz) are becoming crucial in several branches of Astrophysics. All projects in Cosmic Microwave Background research in this region of the spectrum (Planck Surveyor - ESA space mission, Clover, ...) are in need of accurate knowledge of the beams of the instrument. The beam characteristics are not only resulting from the reflectors of the telescope but will also depend strongly of the instrument (detectors, cold optics) coupled to these mirrors. The instrument will introduce some systematic effects that have to be modelled and predicted to allow an accurate data analysis.

The project will be based on the use of optical software complemented with experimental data in order to build a reliable model. The student will also take part in the experimental activities in the laboratory and in real astronomical instruments. The results will be applicable on several present and future astronomical experiments in which our group is already involved.

The FAST (Five hundred meter Aperture Spherical Telescope) project will lead to the largest single dish telescope in the world. Its illuminated aperture in normal operation mode will be 300m in diameter and with special feeding mechanism, the whole 500m aperture could be used. FAST will cover frequencies from 70MHz to 3GHz, and observe at zenith angle of up to 40 degrees without a notable gain loss. As the most sensitive single dish radio telescope, FAST will be a powerful tool for several research domains such as the search for mega-masers and pulsar timing measurements. China has started to build this new telescope with a commission date of 2014 and is planning for the instruments that will be installed at its focus. While the ultimate instrument will probably be based on phased arrays, technology which is not mature enough yet, the first instrument will be based on known and proven technology. Together with NAO (China) and CSIRO (Australia), our group at JBCA (Jodrell Bank Centre for Astrophysics) is starting the study of a 19 pixels receiver array which will form the first focal instrument of FAST.

The project will consist of:

• Define the overall concept of the first receiver system and contribute to the design of the components.
• Prototyping of component and manufacture of one pixel
• Performing the characterisation of the prototype pixel
• Developing the full receiver system

The RadioTechnology group at JBCA is involved in an international collaboration working on a new concept of bolometric interferometer. It is well known that cooled bolometers are the most sensitive detectors for frequency range 90 GHz to 600 GHz. Up to 1 THz they are still largely competitive if not more sensitive than heterodyne detectors. Most, if not all, present bolometric instruments make use of re-imaging optics (such as reflector systems). While these bolometric imagers form the most sensitive CMB experiments, they suffer from instrumental systematic effects, in particular for subtle polarisation effects, which potentially limit their performance. Another approach is to apply interferometric techniques (without reflectors) to this type of detector, making a very “clean” and sensitive instrument.

After the first demonstrator concept already developed (MBI), the QUBIC collaboration (http://www.qubic.org/) is working on the definition of a full instrument which could be developed for the Dome C – Concordia Antarctica base. This experiment will be dedicated to the detection of the Cosmic Microwave Background B-mode polarisation (http://www.jodrellbank.manchester.ac.uk/research/cosmos/cmb.html). If proven successful this concept could also be applied to the future ESA/NASA space mission devoted to the B-mode polarisation.

The PhD project will consist of:

• Contribution to the overall instrumental design
• Focusing on the detailed design of the focal plane, in particular the optics optimisation using Electromagnetic software packages.
• Development of prototypes
• Components and systems experimental characterisation in conjunction with our international collaborators.

Micro electrical mechanical systems (MEMS) devices are used in a number of applications within physics and industry, the emphasis of this project is the applications a device like this can have within astrophysics, and more specifically, integration into experiments that aim to measure the polarization of the Cosmic Microwave Background (CMB) in search of primordial gravitational waves.

The polarisation of the CMB is caused by the Thompson scattering of photons by electrons near the last scattering surface during recombination and the polarization exists in two components E-mode and B-mode. The origin of the B-mode is entirely by primordial gravitational waves and could provide a valuable insight into the inflationary period of the big bang; however the B-mode polarization is predicted to have a small amplitude and requiring sensitive instruments to be able to detect it.

The MEMS radio frequency (RF) Membrane Bridge will make up a phase switch that will be used to separate the polarisations, then used to calculate the Stokes’ parameters which characterise the polarisation of the B-mode. Noise and other sources of interference need to be minimised as the device must be sensitive in order to measure B-mode polarization. The devices typically used in this type of RF experimentation are complex devices that usually involve cryogenics and rely on a great deal of precision. MEMS switches have already demonstrated lower insertion loss and low parasitic and represent a good option for RF research.

This project is to fabricate and characterize the polymer MEMS membrane switch and other similar devices. These devices will be fabricated using high tech nano technologies such as electron beam lithography and new state of the art materials that have been developed at JBCA.

The properties of the materials in nature are determined by how the atoms respond to electric and magnetic fields. Their average behaviour is summarised in the permittivity and permeability values associated with them. However, in principle it is possible to create artificial materials building periodic three-dimesional structures where the sub-wavelength unit elements are designed to respond strongly to the electromagnetic radiation. These 'metamaterials' can be made using planar metallic grids deposided on dielectric substrates stacked together to form three-dimensional structures.

In this project we propose to develop quasi-optical devices for application in millimetre and sub-millimetre astronomy polarimetry. Artificial birefringent materials will be investigated to build quasi-optical retarders such as half-wave plates. The devices requirements will depend on the specific astronomical application under study.

The 'metamaterials' modelling will be done using electromagnetic finite element analysis software such as Ansoft HFSS. Additional codes will be developed to design the quasi-optical devices. These will be manufactured within the group facilities and then tested using coherent detection with a Vector Network Analyser.

An EPSRC grant has been awarded to carry out this development and to investigate also other novel devices. The applications of this work range from mm and sub-mm astronomy (such as future space mission dedicated to CMB B-mode polarisation) to telecommunications, radar systems, etc..

The PhD research project will consist in:

• Electromagnetic modelling using finite-element analysis
• Design of novel half-wave plates and other retarders
• Clean room processing and manufacture of the devices
• Millimetre wave Vector Network Analyser testing and characterisation

In this project we propose to develop high performance systems based on waveguide and microstrip devices for application in millimetre and sub-millimetre astronomy with particular focus on polarimeter components. Devices like ortho-mode transducers, phase-shifters, polarisation modulators and filters can be developed using both waveguide or planar technologies. The electromagnetic requirements of the devices will depend on the specific astronomical application under study.

The modelling and the design of the devices will be done mainly using electromagnetic finite element analysis software such as Ansoft HFSS. The devices will be manufactured and then tested using coherent detection with a Vector Network Analyser.

Particular emphasis will be spent in designing devices suitable for focal plane arrays that require high level of integration and the possibility to be mass produced at reduced costs. This development find applications in the future space mission dedicated to CMB B-mode polarisation or in large format arrays that will be used in radio telescopes.

The PhD research project will consist of:

• EM modelling with finite-element analysis
• Design of novel waveguide/microstrip components
• Optimisation for large arrays
• Vector Analyser testing

The next generation of CMB polarisation B-Mode experiments require very high sensitivity. Developing very large (and expensive) focal plane arrays is a natural way to proceed although other possible solutions could be adopted using multi-mode antennas: they allow to collect more photons than a conventional single-mode antenna. The development of these devices goes in parallel with the development of multi-mode detectors and optics. Even if multi-mode horns antennas have been adopted in the past for intensity measurements (as in the Planck satellite mission), they have not been used for polarisation measurements. The polarisation behaviour of these devices and their detectors still needs to be investigated in details: this field is at its early stages of study.

In this project we propose to study and develop new multi-moded horn antennas and associated bolometric detectors to be used in polarisation measurements. Successfull devices of this kind will find immediate application in next generation of experiments dedicated to CMB B-mode polarisation. A new balloon-borne experiment (LSPE) is being developed by Italy with JBCA as a collaborator. This experiment will make use of multi-mode pixlels.

This PhD research project will consist in:

• EM modelling with finite-element analysis and physical optics
• Design of new multi-mode systems
• Development of dedicated testing facility
• Vector Analyser and cryogenic testing