MSc projects
Projects can be designed and agreed at the interview stage through discussion with staff. Below are examples of projects already proposed.
The Behaviour of Cold Gas in Galaxy Mergers
Nicky Brassington and Elias Brinks
It is widely believed that very few galaxies exist today that have not been formed or shaped in some way by an interaction with another galaxy. These interactions play a major role in the evolution of galaxies by triggering star formation and nuclear activity. However the parameters that influence the star forming activity in interacting galaxies are poorly understood.
In this project the student will work with HI data of up to 10 galaxy pairs, which have been selected from the the Spitzer Interacting Galaxies Survey (SIGS), a large international collaboration studying a large sample of 110 galaxies in different stages of interaction with the Spitzer Space Telescope. These ten systems have been selected to contain one gas-rich and one gas-poor galaxy over a range of merger stages.
These data are all currently in the VLA archive and the student will be involved with using the newly implemented pipeline to reduce these observations. From this analysis the effect of galaxy interactions on the cold gas content of these systems can be observed and compared to the properties of HI gas in interacting systems containing two gas rich galaxies.
Using GANDALF the resolve star formation history of nearby galaxies
Marc Sarzi
Gandalf is a Gas and Absorption Line Fitting code that is now widely used to match in detail both the stellar and nebular contribution to the optical and near infrared spectra of galaxies. It is mostly used to derive the gas kinematics and to clean from the nebular emission the underlying stellar spectrum of galaxies, allowing to infer the mean age and metallicity of a galaxy stellar population by measuring the strength of various absorption-line features that form in the photosphere of stars.
When astronomers do not dispose of optical spectra they rely instead on broad- or narrow-band images to infer the stellar content of galaxies, which is much cheaper in terms of exposure times. In fact, even though the detailed photospheric information is lost in such coarse observations, such an imaging allows to cover a longer wavelength range from the ultra-violet to the far infrared, which are extreme regimes that are sensitive to the presence of very young stars or cold interstellar dust, respectively.
So far, only rather simplistic attempts have been made to combine the information carried by both the optical spectra and the more extended broad-band imaging, but the result of these experiments were already very promising.
In this MSc project, a student will work to modify Gandalf so that it can deal with both spectra and broad- or narrow band photometric data, thus building for the first time a tool that can fully and rigorously extract the information of the stellar population content of galaxies that is carried by both optical spectra and imaging at both shorter and longer wavelengths.
The student will then apply this tool to the SAURON sample galaxies, for which integral-field spectroscopic observation provide spectra across the entire optical regions of this objects, which, once combined to near-UV and Infrared images, will allow to constrain – for the first time - the star-formation history of these galaxies in different galactic regions.
Extra-Galactic PNe with Integral-Field Spectroscopy
Marc Sarzi
In extra-galactic astronomy, Planetary Nebulae (PNe) are generally regarded as useful indicators for the distance or dark-matter content of their galactic hosts. Yet, PNe can also be powerful probes for the properties of their parent stellar population and are key to our understanding of how much stellar mass is returned to the interstellar medium, a crucial element in the life-cycle of galaxies.
As of today, most known extra-galactic PNe have been found in the outskirts of their host galaxies, because they were observed with narrow-band imaging or slit-less spectroscopy that find it hard to detect PNe against a star-light background. Yet, it is in the central regions of galaxies that the age and metallicity of stellar populations show the largest variations within a single galaxy or between different objects.
Integral-field spectroscopy (a young and fast growing technique in astronomy) can overcome such instrumental limitation since it allows for a careful subtraction of the galaxy spectrum, as demonstrated by Sarzi, Mamon et al. (2010) and Pastorello, Sarzi et al. (2012) in the case of our closest companions M31 and M32, respectively, using SAURON data.
This MSc project will extend such first experiments to the entire SAURON sample of 48 early-type galaxies (de Zeeuw et al. 2001). Since the stellar population properties of these galaxies are already known (Kuntschner et al. 2010) this work will be the first systematic investigation of the link between the PNe content and the stellar populations of early-type galaxies. Following this work, the student may be then be in an optimal position to further investigate extra-galactic PNe by exploiting - in the context of a possible PhD - the next generation integral-field spectrograph MUSE, which will be mounted on VLT by late 2013.
AGN-driven Outflows in Nearby Galaxies
Marc Sarzi
Over the course of the last two decades the detections of almost 50 supermassive black holes (SMBHs) has established that these objects must be an integral part of most galaxies. In fact, most models for the hierarchical formation of galaxies now invoke SMBHs in order to match the observed luminosity function of galaxies and avoid over-predicting the number of bright object, by requiring SMBHs to quench star formation. Such feedback mechanism is supposed to happen when SMBHs accrete gas and become active nuclei (AGNs), but in practice there not much direct evidence for AGN feedback playing a significant role in galaxy evolution.
The goal of this MSc project is to directly test whether AGN feedback is actively shutting star formation in nearby massive early-type galaxies, by seeking evidence of gas being evacuated from the galaxy.
When outflows occurs in galaxies, for instance in star-bursting systems such as M82, neutral material can also be entrained in the flow and can be observed against the stellar background of the galaxy by detecting characteristic absorption lines corresponding to the wavelengths at which some specific elements absorb light. In the optical spectrum the strongest of such interstellar absorption lines are due to the sodium NaD doublet at 5890,5896 Angstrom. If AGN feedback is shutting down star formation in ETGs by driving gas outflows we should observe an excess of NaD absorption compared to what observed normally in stellar photospheres, which should be generally blue- or redshifted compared to the position of the stellar NaD absorption line.
The student will use the GalaxyZoo database to select a large sample of morphologically selected ETGs and use the emission-line fitting code Gandalf (Sarzi et al. 2006) to not only fit the stellar continuum and the nebular emission, but also to match the NaD region by adding negative Gaussian components and thus assess the presence and position of a possible NaD interstellar component.
Probing the formation of OB associations from their current structures
Nick Wright
It is currently heavily debated as to whether stars only form in dense groups known as star clusters or whether they can also form in low density groups or even in isolation. This is an important question for theories of star formation as well as for our understanding of how high-mass stars influence their surroundings, including the evolution of low-mass stars. To address this question we are studying low density groups of young stars known as OB associations to search for evidence that they formed in a more clustered distribution or whether they have always existed in a low density form.
This project will involve studying nearby young OB associations using existing catalogs compiled from the astrometric space mission Hipparcos. This data will be used to study the spatial structure of the OB associations using a number of mathematical algorithms. This will provide an indication of the dynamical state of these groups of stars, which in turn will provide clues to their origin as either dense clusters or as diffuse, low density sites of star formation.
Surface Chemistry of Asymptotic Giant Branch (AGB) Stars in IPHAS
Nick Wright
The late stages of stellar evolution of solar and intermediate mass stars are characterised by dramatic changes in luminosity, effective temperature and surface abundances. These changes are induced by the switch from stable core hydrogen burning to unstable shell burning of hydrogen and helium when the core supply of hydrogen and helium has been exhausted. During this asymptotic giant branch (AGB) phase the products of nuclear burning are brought to the surface of the star in dredge-up events, therefore changing the surface composition and influencing the products of nuclear burning that are returned to the interstellar medium at the end of the star's life.
This project will involve studying optical spectra of a large sample of AGB stars gathered as part of the IPHAS survey and classifying them on an existing classification system. The spectra include both oxygen-rich and carbon-rich stars, as well as the intermediate S-type stars. Once the sample of stars has been classified the spectral properties of the stars can be compared with their photometric properties from the IPHAS survey. Previous work has suggested a correlation between the photometric properties of a star and its surface chemistry. If this can be confirmed it will allow surface chemistries to be estimated for millions of stars in our Galaxy from photometric information alone, a more efficient method than obtaining spectra for all of these stars. This has a number of possible benefits, including acting as a met.