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PhD projects offered

I am not offering any specific projects at the moment, but I’m open to discussing ideas related to my present research. If you are interested in working with me please do get in touch and complete an official application, ideally before the end of January.

See here for the full list of PhD projects offered by the University of Nottingham astronomy group.

Previously offered projects

These were offered in previous years, but are no longer available (sometimes because I now have a student working on them).

Beyond the morphology-density relation

It has been known for almost a century that passive, red, early-type galaxies (ellipticals and lenticulars) preferentially inhabit denser regions of the universe. The proportion of star-forming, blue, spiral galaxies in such regions is correspondingly suppressed. Various lines of evidence indicate that many spirals must have been transformed into early-types over the past few Gyrs. However, identifying indicators of that transition within the spiral galaxy population has been surprisingly elusive. One of the clearest signs is the presence of red spirals, galaxies which possess spiral morphology but are no longer forming stars at the rates typical of most spirals. The existence of this class of galaxies indicates that morphology and recent star-formation history are partly independent characteristics. However, it is not clear whether this independence is simply a result of different timescales, or whether the morphological and star-formation rate transformations are caused by disparate physical processes. Population statistics seem to require that red spirals become early-types eventually, but is this a consequence of the decline in star-formation rate, or brought about by subsequent interactions? Studying the variation in spiral structure (e.g., prominence, number, pitch angle and length of the spiral arms) with environment and star-formation history offers an opportunity to answer this question. This project will draw on a unique combination of data at low and intermediate redshifts, provided by both Galaxy Zoo and automated methods.

The most extreme galaxies in the Universe

Some varieties of galaxies, that are nowadays rare and possess seemingly extreme properties, were common at high redshift. Identifying examples of these galaxies, at sufficiently low redshift that they can be studied in detail, allows us to gain an understanding of processes which were important in the early Universe, but are currently extremely difficult, or even impossible, to directly observe. An excellent example is the `Pea’ galaxies, identified by Galaxy Zoo and subsequently studied by several groups. For their mass, which is typical of galaxies at high-redshift, these are the most extremely star-forming objects in the Universe. We have pioneered techniques to detect these objects both at low and intermediate redshifts, in an attempt to characterise their properties and trace back their relationship to early star-forming galaxies. This project will continue this investigation, using statistical analyses to determine the link between populations at different epochs and direct observations to better understand the nature of these systems.

Unravelling galaxy components

The majority of galaxies comprise two basic stellar components, a bulge and a disk, with contrasting properties and origins. This distinction between spheroid and disk stellar components is at the heart of our models of galaxy formation. In these, galaxies grow through two principle mechanisms: the gradual accretion of gas, which cools and settles into a thin disk in which stars form; and the merging of existing stellar systems, which result in a spheroid. These two components therefore represent disjoint periods in a galaxy’s history. Observationally distinguishing the physical properties of bulges and disks, and measuring their separate dependence on mass, environment and cosmic time, is fundamental to a full understanding of galaxies.

We have recently developed a revolutionary method (MegaMorph) for decomposing spheroids and disks using data from modern surveys. This PhD project will involve applying this new technique to the latest high-resolution, multi-wavelength surveys at both low- and high-redshift, in order to uncover how the assembly histories of galaxy components depend on one another and their wider environment. This will enable a deeper appreciation of how the standard scaling relations and distributions of galaxy properties arise.

At low redshift this project will use data from the GAMA survey, particularly imaging from VISTA-VIKING and VST-KIDS. At high redshift, it will utilise a variety of HST surveys, including CANDELS. It will also draw on visual classifications from Galaxy Zoo to support the quantitative morphological decompositions.

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