Edinburgh PhD Projects 2003

The following is a brief list of PhD Project proposals for October 2003. See the home pages of relevant staff, plus the research pages, for background detail.

All our studentships for 2003 are now allocated, so students wishing to work on these projects would need to bring their own funding.

Title: Coupled black-hole and spheroid formation in the young universe.
Supervisors: James Dunlop, Ross McLure, Marek Kukula

Over the past few years we at Edinburgh have undertaken a major Hubble Space Telescope (HST) study of nearby quasars in an effort to determine both the nature of their host galaxies, and the masses of the central black holes which power these most luminous of active galactic nuclei. This work has shown that quasars appear to display the same linear relation between black-hole mass and host spheroid mass as inactive ellipticals, namely

M(black hole) = 0.001 M(host spheroid).

This remarkably simple relation now appears to apply over a wide range (6 orders of magnitude) of spheroid/black-hole masses, and consequently many astronomers now believe that the formation of supermassive black holes and the spheroidal component of their host galaxies must be intimately connected.

However, at present very basic questions about the nature of this connection remain unanswered - for example it is not known if black-hole and host-galaxy growth proceed in tandem, or if one precedes the other. To remedy this situation we now propose to determine the relationship between black-hole and host-galaxy mass at high redshift, z > 2, which many lines of argument now indicate corresponds to the epoch of spheroid formation.

At such redshifts it is utterly impossible to measure the mass of a central black hole within a quiescent galaxy from stellar dynamics (as has now been done for ~30 nearby galaxies). However, we have recently shown that it CAN be done for quasars using the observed widths of their optical/UV emission lines. Thus, if we can also determine the masses of the hosts of high-redshift quasars we will be able to determine how the relationship between black-hole mass and host spheroid mass depends on cosmic epoch. We thus propose a two-pronged PhD project which aims to combine

1) estimates of the black-hole masses in high-z quasars derived from optical/near-infrared spectroscopy

2) estimates of the host galaxy masses of high-z quasars derived from detailed modelling of deep, high-resolution, multi-colour imaging.

With the advent of deep, high-resolution optical/near-infrared imaging/spectroscopy on 8-m class telescopes this project is now technically feasible, and so the time is right for a PhD student to commence work in this area. Moreover, with the UK joining ESO and thus gaining access to the four 8-m telescopes of the VLT in Chile from Spring 2003, we anticipate being able to undertake the necessary deep observations for a statistically significant sample of objects.

Title: The Fanaroff & Riley class I/II divide in radio-loud Active Galactic Nuclei
Supervisors: Ignas Snellen & Philip Best

A small fraction of galaxies exhibit strong activity at radio wavelengths, believed to be associated with matter accreting onto a supermassive black hole in the centre of the galaxy. These radio-loud active galaxies exhibit a very distinct morphological difference between low and high radio power sources - the Fanaroff & Riley (FR) type I and II. It is unclear whether this is caused by fundamental structural differences in their central engines, such as the rate or type of accretion, or the spin of the massive central black hole. Several observational differences have been claimed to be found, including the properties of the host galaxy, their optical emission lines, and cosmological evolution. However, most of these results have recently been brought into doubt.

This PhD project will be centered around a new deep radio survey conducted with the Very Large Array designed to address these issues by determining for the first time directly the cosmological evolution of FR I radio galaxies, and by comparing the properties of the FR I/II divide at high redshift with that in the local universe.

Title: Mapping the Distribution of Dark Matter with Gravitational Lensing
Supervisors: Andy Taylor, Alan Heavens

The question of what is Dark Matter remains one of the major problems of physics. Ultimately we can hope that its detection in a laboratory will reveal its true nature and place in physics. At the moment our only guide to its properties is from Cosmology. Gravitational lensing, where light is bent by the gravitational field of matter, provides us with a direct probe of where Dark Matter is in the Universe. Edinburgh has long been at the forefront of developing and applying methods to image the distribution of Dark Matter from lensing and studying its properties.

Gravitational lensing is traditionally studied by looking at the alignments of galaxy images on the sky, ignoring the distances of the individual galaxies. With photometric redshifts, one has some distance information, which can be used, for example, to measure cosmological parameters more accurately, such as constraining the equation of state of vacuum energy. We are looking for someone to develop the 3D lensing techniques which we are pioneering in Edinburgh, and to apply them to COMBO-17 and other datasets.

Title: Modelling galaxy formation & clustering
Supervisors: Will Percival & John Peacock

Although galaxies provide one of the key tracers of cosmological structure, the processes which control galaxy formation and evolution are complicated, and are not fully understood. There are many different types of galaxy, and these different types have different evolutionary histories and clustering properties. The most common way to model galaxy formation is through complex numerical simulations, which try to model all of the important processes at once. However, insight into which are the key processes often comes instead from simple analytic models. Additionally, analytic calculations provide exact solutions rather than noisy approximations, and these models can often be folded into the numerical simulations to increase their speed and accuracy. This project aims to create and test analytic models of aspects of galaxy formation.

An example area which could be studied is the small scale clustering of galaxies. We know that, on large scales, clustering only depends on the average mass of halo within which the galaxies reside. On small scales there are two further complications. Two or more galaxies may exist within a larger mass object increasing the pair counts on small scales. Additionally, the clustering properties of the average halo within which the galaxies reside may depend on halo properties (and consequently galaxy properties) other than the halo mass. By combining high resolution simulations with analytic models of cosmological mass growth it should be possible to determine the relative importance of these two effects.

Title: SCUBA-2: A "CCD-style" camera for submillimetre astronomy
Supervisor: Wayne Holland

SCUBA-2 is a new camera under development for the 15-m James Clerk Maxwell Telescope in Hawaii. It will incorporate new generation superconducting detector arrays with a innovative multiplexed signal readout scheme, to produce what is effectively the world's first "CCD camera" for submillimetre astronomy. SCUBA-2 will image the sky some 1000 times faster than any other instrument. Scientifically, SCUBA-2 will address some of most fundamental 'origins' questions: how galaxies, stars and planets form.

By October 2003 the project will have demonstrated the performance of prototype arrays. Early in 2004 the final instrument will be assembled and tested in the lab in Edinburgh, before delivery to the telescope in late 2005. The student will be closely involved in this work gaining experience in detector technology, low-noise analogue and digital electronics, cryogenics and instrument evaluation techniques. The student will also have the opportunity to become involved in the science programme definition.

Title: MIRI: a mid-infrared spectrometer for the James Webb Space Telescope
Supervisor: Gillian Wright

We seek a student to work on instrumentation for the James Webb Space Telescope (JWST), the successor to the Hubble Space Telescope. Scheduled for launch in 2011, the JWST's primary science objectives are detecting the first generation of starts (first light), formation of stars and planetary systems, and evolution of planets and the conditions for life. To achieve these goals, the JWST will require much more light-gathering capability than Hubble, and will be equipped with near and mid-IR instruments. At approximately 6 meters in diameter, JWST's primary mirror will be more than two-and-a-half times as large as the Hubble telescope, and it will be the largest space telescope ever flown.

Gillian Wright is leading an international partnership to provide the European Optics Module for the mid-infrared instrument, MIRI. Here in Edinburgh we will be responsible for designing and building a spectrometer pre-optics unit containing a set of four image slicers. Image slicers are a relatively new technique in spectrometers which enable the study of spatial and spectral information simultaneously. The image slicers will be based on ones developed at the ATC for the UIST instrument, but no image slicer has ever been shown to work at mid-IR wavelengths.

The student will work closely with the JWST team at the ATC on the design and testing of a mid-IR image slicer. In the process you will learn about the techniques for building astronomical instruments in space, optical design, diffraction, cryogenics and instrument evaluation techniques. You will also take part in research at Gemini and UKIRT on science that lays the foundations for future research with the JWST, using the UIST image slicer to study nearby galaxies in infrared absorption lines, coupled with mid-IR spectroscopy using Michelle on Gemini.

Title: The development of galaxy clustering
Supervisors: John Peacock, Stefanie Phleps, Andy Taylor

Redshift surveys of the local galaxy distribution, such as the 2dF Galaxy Redshift Survey have given an accurate picture of the distribution of galaxies out to redshift 0.2. The results are consistent with a universe dominated by "cold" collisionless dark matter, with a density of approximately 30% of critical. This progress poses a set of new questions, which will be addressed by future work at Edinburgh. There is scope for a PhD student to be involved in a number of the following elements:

Title: Where are the baryons now? - the detectability of the warm/hot intergalactic medium with Planck
Supervisors: Bob Mann, Alan Heavens, John Peacock

Models for Big Bang Nucleosynthesis predict the amount of normal, baryonic matter that should exist in the Universe today. Observations at high redshift (z>2) indicate the presence of roughly the predicted baryon density, mainly in the form of diffuse, ionized gas in the intergalactic medium. By contrast, a corresponding census at redshift zero reveals a deficit; summing the baryon density in known systems of stars and galaxies yields a result some 30-40% lower than predicted. So, where are these missing baryons?

Hydrodynamical simulations of the formation of large-scale structure may have the answer. They predict that roughly the correct density of baryons should be found in a "warm/hot intergalactic medium" at temperatures of 105 - 107 K that traces the same filamentary pattern of large-scale structure as the galaxy distribution. Such gas is very difficult to detect: it's too hot to have condensed into stars, and too cool and diffuse to emit significant X-ray radiation. It might, however, be detectable through the effect it would have in scattering cosmic background radiation (CBR), via the Sunyaev-Zel'dovich effect. The signal of this effect would be weak, but initial studies suggest that it might be detectable by cross-correlating galaxy clustering data furnished by the coming generation of optical/near-IR sky surveys with CBR data from Planck, a European Space Agency mission to be launched in 2007.

We seek a student to study the feasibility of detecting this signal in detail. This will involve running large-scale numerical simulations,and developing new techniques for the efficient computation of cross-correlation statistics to analyse results from them. This project would make use of the exceptional computational resources available in Edinburgh, and would suit a student comfortable with both computational and mathematical work.

Title: Projects with the Sloan Digital Sky Survey
Supervisor: Avery Meiksin

Principal topics related to the Sloan Digital Sky Survey are galaxy formation and evolution, and the spectra of quasars, the latter primarily in connection with probing the evolution of the intergalactic medium (the Lyman-Alpha forest).

Galaxy formation projects would involve the comparison of the Sloan galaxy spectra with the predictions of semi-numerical models of the evolution of galaxies in order to constrain the star formation history of galaxies in the context of cosmological models for structure formation. Topics to explore include the relation of galaxy types to environment, the role of metal recycling within galaxies, and the evolution and environmental dependence of the initial stellar mass function of galaxies. Most of my interest currently focusses on the spectra of the galaxies, but making a connection to galaxy morphology would be possible as well.

A second area involving the Sloan is the spectra of quasars. The Sloan has detected QSOs out to a redshift of over 6. The spectra of these QSOs provide an excellent opportunity to trace the evolution of the gas between galaxies, the so-called intergalactic medium (IGM). This is the gas that falls into galaxies as they form, and in turn is affected by the galaxies through the winds they generate during bursts of star formation by returning some of the gaseous content of the galaxies back into the IGM. It is possible the galaxies also maintain the ionization of the IGM, though QSOs will also contribute substantially to this. A topic of great current interest in the subject is the era of reionization of the gas. Current evidence suggests the IGM was reionized near a redshift of 6, an epoch the Sloan probes. Much of the work would entail estimating the continuum flux of the QSOs, which act like beacons, the light of which is absorbed by the intergalactic gas and so enabling the IGM to be `seen' in absorption (the Lyman-Alpha forest). The key is to know how much of the continuum light of the QSO is absorbed in order to trace the behaviour of the intervening IGM gas. At the same time, learning how the continua of QSOs change with redshift tells us about the evolution of the QSOs themselves. Depending on the interest of the student, this project could also have a substantial theoretical component involving the numerical simulation of the evolution of the intergalactic medium.

Title: Galactic structure from stellar proper motions
Supervisors: N Hambly & J Cooke

Stellar proper motions measured to faint limits over wide angles enable detailed studies of the structure of our Galaxy. Luminosity functions (and hence mass functions) of various kinematic populations and different luminosity types can provide clues as to the contribution to total mass made by different populations, and also to the possible contribution of stellar remnants to dark matter problems. We have a number of wide field datasets available at Edinburgh that can be employed in such work. Example topics to be studied may include:

i) There is some evidence for a population of cool white dwarf stars in the halo of our Galaxy. This has important implications for halo dark matter models, disk rotation curves and the evolution and structure of spiral galaxies. White dwarfs provide a natural candidate for the MAssive Compact Halo Objects (MACHOs) that are observed in microlensing experiments. The wide field datasets will be used to measure the space density of these stars. It will then be possible to measure to what extent cool white dwarfs contribute to the total halo mass density required to explain the MACHO and rotation curve results.

ii) The hypothesis detailed in i) is naturally controversial. It is currently uncertain as to the contribution of the old disk and thick disk components to the population of high velocity, cool white dwarfs. The same wide field datasets can be used to examine the cool stellar members of these respective populations.

It will be possible to draw some conclusions as to the star formation history of the distinct kinematic components of the Galaxy, and to refine their age estimates, for example by removing thick disk and halo contamination from the disk WD luminosity function.

This project will involve extensive use of computers to process large catalogue datasets. It is probable that some experience will also be gained in follow-up observations of stellar objects using large aperture telescopes.

Title: RAVE: the radial velocity experiment
Supervisor: Mike Hawkins

Starting in April, the UK is spear-heading an international collaboration to measure the radial velocities of some 50 million stars with the idea of mapping out the detailed velocity structure and chemical make-up of the Galaxy. The scientific pay-off of this project will influence many areas of astrophysics and cosmology, including new insights into the formation of the Galaxy, its subsequent history and pesent day structure, limits on the presence and distribution of dark matter, and a better understanding of merging processes. Edinburgh will be playing a leading role in the project, starting with a pilot survey of 100,000 starts which is already scheduled for the coming year and will be used to map the structure of the thick disc, as well as providing a template for the all sky survey.