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Astrophysics

This page lists all the PhD projects offered by Astrophysics group, separated according to the following research areas: Galaxies (including our own!), Massive Stars and Clusters, Low-mass Stars, Star Formation and Astrochemistry, Exoplanets, Cosmology;

Galaxies



Galaxy formation

I will be offering several projects on galaxy formation, involving the  study of classes of distant galaxies in order to determine their physical properties, such as mass, sizes, kinematics, and star formation properties. The molecular gas in these galaxies, its physical and chemical properties, is of particular interest as this governs the star formation (and thus the formation process) of galaxies.

Contact: Dr Thomas Greve (tgreve@star.ucl.ac.uk)


Cold gas as a probe of galaxy evolution

One of the biggest impediment in our understanding of galaxy evolution is our relatively poor knowledge of the cycling of gas in and out of galaxies: how gas is accreted onto galaxies, processed into stars, and then returned to the circumgalactic medium. Fortunately, it is now possible to directly observe cold gas in large samples of galaxies and therefore to overcome this difficulty. Cold gas also has the advandage of being a senstive probe of the different mechanisms that can affect the evolution of galaxies. In this project, you will use data from a new large multi-wavelength survey targeting low mass galaxies and robust statistical methods to understand the balance between gas and star formation in these systems. The project, mostly observational in nature, will also include observations at optical, millimeter and radio facilities, high resolution follow-up work with ALMA, and will link with current work in high redshift galaxies which share common properties (low masses and low metallicities).

Contact: Dr Amelie Saintonge (amelie AT star.ucl.ac.uk)

Studies of dust and molecules in supernova remnants

From Herschel Guaranteed Time observations of young supernova remnants
(SNRs), we have detected large quantities of cool dust in the remnants of
several young core-collapse supernovae (CCSNe), including the ejecta of SN 1987A in the LMC, and in our own galaxy the 330-yr old Cas A and the
960-yr old Crab Nebula. In each of these remnants between a tenth and
four-tenths of a solar mass of cold dust has been detected. This exceeds
the 0.1 Msun of dust per SN that has been estimated to be necessary if
supernovae are to influence the dust content of galaxies, particularly
those of galaxies at high redshifts, which are too young for low mass AGB stars to have produced the observed quantities of dust.

The PhD project will combine (1) a deep analysis of our Herschel
photometric and FTS spectral datasets on young CCSN remnants in order to
spatially map the coolest and most massive dust components present, along
with (2) detailed modelling of the ionic, molecular and dust emission from
the remnants using shock collision and radiative transfer modelling codes.
There may also be the opportunity to obtain complementary ground-based
optical and infrared observations of selected SNRs. The goal of the
project is to quantify and to understand the evolution of the dust and
molecular content of young core-collapse supernova remnants. 

Contact: Prof Mike Barlow (mjb AT star.ucl.ac.uk)


The origin and nature of molecular emission in galaxies

It is now well established that chemistry in our own galaxy as well as
in external galaxies can be complex and well-developed. In particular,
molecular emissions can be used to explore the physical conditions and the likely evolutionary status of near and far away galaxies. The project on offer will be a mixture of data analysis of nearby galaxies (taken with ALMA and JCMT) and astrochemical modelling with the aim of using multi-species
multi-transitions molecular emissions as a tool to
'disentangle' the multiple and  spatially unresolved gas components of different types of galaxies (e.g. starburst, AGN, ULIRGs),
with particular emphasis on tracing the dense star forming gas within a galaxy.

Contact: Prof Serena Viti (sv AT star.ucl.ac.uk)


Galaxy formation as a probe of fundamental physics

Galaxies are the fundamental building blocks of the universe. Their internal structure provides critical tests of the dark matter paradigm; they are responsible for the reionisation of the universe; and their distribution on cosmological scales is a key discriminant between competing theories of, for example, dark energy. But extracting the desired information requires a better understanding of the combined dynamics of dark matter, gas and stars in a cosmological setting. As part of an international collaboration, this project will explore the ever-shifting interface between theory, observation and computation. There are opportunities to focus on the galaxy formation physics, on metal enrichment of the intergalactic medium, or on the application of new ideas in these areas to galaxy survey design and exploitation. 

Contact: Dr Andrew Pontzen (a.pontzen AT ucl.ac.uk)

Searching for dust factories in the Milky Way

The Herschel Space Observatory operated from 2009 until 2013 observing the universe in the very far infrared part of the electromagnetic spectrum: 57-700 microns in wavelength. By observing at these wavelengths we werre sentive to the coldest material present in our own and neighbouring galaxies. One of the most extensive observing programmes undertaken by Herschel was the HiGAL survey of the plane of our own Milky Way galaxy. These survey data have been used to uncover the earliest phases of star formation and allowed us to view the delicate ribbons of cold dust that permeate the Interstellar Medium (ISM) between the stars. The origin of the dust in the ISM is thought to be mostly due to the formation of dust grains in the winds of highly evolved Asymptotic Giant Branch stars (AGBs). This project will use the data from HiGAL and other large surveys to search for AGB stars and provide observational evidence for AGBs being the prime source of galactic dust.



                                         

Contact: Prof Bruce Swinyard (b.swinyard AT ucl.ac.uk)

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Low-Mass Stars


Molecular line lists for exoplanets and Cool Stars
UCL has been at the forefront of the effort to characterise some of the many extrasolar planets that have been discovered over the last decade. This work requires extensive sets of molecular data to both model observed spectra and as input to model atmosphere codes. Given that many exoplanets are "hot Jupiters" this data must work over extended temperature ranges. At the hot end (T = 1500 - 3000 K) molecular data is also essential for studies of the atmospheres of cool stars and brown dwarfs. The calculation of very extensive line lists using first principles quantum mechanics has been pioneered at UCL were successful datasets have calculated for a number of important molecules (eg water, HCN and H3+) and used for high profile astronomical studies. However there are a number of key systems for which little or no data is available. In particular the hydrogen sulphide (H2S) is thought to be an important constituent of some exoplanets and acetylene (HCCH) molecule is known to be an important constituent of carbon stars. A comprehensive treatment of the spectrum of one of these species at elevated temperatures will be attempted using first principles quantum mechanical methods developed in the group.

Contact: Prof. Jonathan Tennyson (j.tennyson AT ucl.ac.uk)

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Star formation and Astrochemistry


How do brown dwarfs form?

Eight out of 10 stars in our stellar neighbourhood are low-mass stars (LMSs). The astrophysical importance of brown dwarfs and low-mass stars comes from the fields of cosmology (are some of these stars primordial?) and Galactic dynamics (how much mass is stored in faint, low-mass stars?), from the field of star formation (does the initial mass function vary among star formation regions, and is there a lower mass limit below which no "stars" form?) as well as from an area of great current interest, that of extrasolar planets (what distinguishes a brown dwarf from a low-mass star, and an extrasolar planet from a brown dwarf?). And yet, the formation of such 'failed' stars is still under debate. This project involves the use of a star formation model to investigate the different proposed scenario for the formation of brown dwarfs. The project is theoretical but can involve an observational component.


Contact: Prof Serena Viti (sv AT star.ucl.ac.uk);


The formation of low mass metal-poor stars

Very recently,  an extremely metal poor low mass star has been discovered (Caffau et al., 2011, Nature), implying the possibility of forming low mass stars in an almost zero metallicity environment, something that until not long ago was thought not to be possible as the star formation timescale, among other things, would have been impossibly long (see Banerji et al. 2009).   This project will adapt and make use of a suite of chemical models simulating the formation of low mass stars to determine the parameter space of densities, gas:dust ratios, metallicities etc within which primordial low mass stars can form.

Contact: Prof Serena Viti (sv AT star.ucl.ac.uk)


The Elusive Progenitors of Dwarf Carbon Stars

Since their discovery in 1977, very little is known about dwarf carbon stars -- main-sequence stars like the sun dominated by carbon instead of oxygen.  While researchers have hypothesized that a carbon-rich star can give birth to carbon chemistry planetary systems, the working hypothesis is that the dwarf carbon stars are the product of binary star evolution.  However, few such binaries  are known and their properties are poorly constrained.  Furthermore, a significant fraction of dwarf carbon stars appear to belong to the ancient Galactic halo population and thus hold clues to the earliest stages of star formation and binary evolution.  This field is wide open and the project could entail many aspects: establishing a standard classification system, investigating their chemistry with spectral models, establishing kinematical (halo, thick and thin disk) populations, and searching for and measuring their binary fraction, orbital periods, and mass transfer modes.  One might investigate ways to probe for carbon-rich planets in these systems.


Contact: Dr Jay Farihi (jfarihi AT star.ucl.ac.uk)

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Exoplanetary systems

Terrestrial Exoplanets via Asteroid Archaeology

We now stand firmly in the era of solid exoplanet detection via Kepler and other state of the art facilities. Yet the empirical characterization of these most intriguing planets is extremely challenging.  Transit plus radial velocity information can yield density, but the bulk composition remains model−dependent.  An increasing body of evidence demonstrates that polluted white dwarfs can provide the bulk composition of rocky minor planets  (i.e. exo−asteroids), the building blocks of solid exoplanets.  The white dwarf distills the planetary fragments, and provides powerful insight into the mass and chemical structure of the  parent body.  In the Solar System, the asteroids (or minor planets) are leftover building blocks of the terrestrial planets, and we obtain their compositions -- and hence that of the terrestrial planets -- by studying meteorites. Similarly, one can infer the composition of exo-terrestrial planets by studying tidally destroyed and accreted asteroids at polluted white dwarfs.  The project will explore this relatively new and innovative technique and a variety of projects are available. 

Contact: Dr Jay Farihi (jfarihi AT star.ucl.ac.uk)


Molecular line lists for characterising extrasolar planets
The number of extrasolar planets detected is increasing rapidly and attention is turning to determining what they are made of. To do this requires very significant quantities of spectroscopic data which is largely unavailable. A major new project is being launched at UCL to calculated a comprehensive set of molecular line lists that will allow scientists to model the atmospheres of hot exoplanets, brown dwarf and cools stars (see www.exomol.com).

One (or possibly two) PhD students are sort to work in a team of about 6 people on this project. Interested students should have a good understanding of quantum mechanincs and be interested in computational work. The studentships are available to both UK and EU nationals.

Contact: Prof Jonathan Tennyson
web-page: www.ucl.ac.uk/phys/amopp/people/jonathan_tennyson/
e-mail: j.tennyson@ucl.ac.uk

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Cosmology


Imaging and spectroscopic galaxy surveys and their combination as cosmological probes

Galaxy surveys serve as probes of Dark Matter, Dark Energy and other cosmological properties. The Dark Energy Survey (DES), in which UCL is heavily involved has started imaging 5000 sq. deg. of the sky to probe Dark Energy using multiple techniques: galaxy clustering, clusters, weak gravitational lensing and Supernovae Ia. On the other hand the Dark Energy Spectroscopic Instrument (DESI) will measure galaxy spectra over nearly half the sky. The PhD project will focus on the interplay of spectroscopy and imaging of DES, DESI and other future projects such as Euclid and LSST. In particular the project will explore how the above probes can distinguish between Dark Energy models and modifications to General Relativity. The student will be part of TESTDE, supported by an Advanced European Research Council Grant. 

Contact: Prof Ofer Lahav (o.lahav AT ucl.ac.uk)


The 21cm neutral hydrogen radiation from the first stars and quasars

The LOFAR array has been now comisioned and is currently producing data on its shallow Million Source Sky Survey, the MSSS. Shortly after it will start producing data for the individual Key science projects one of which is hunting for the epoch of reionisation. This project will be hunting for the signal imprinted onto the 21cm neutral hydrogen radiation from the first stars and quasars formed in the Universe. An example project would use data from this survey to look for statistical significant detection of this signal in the radio part of the spectrum.

Contact: Dr Filipe Abdalla (fba AT star.ucl.ac.uk)


Understanding the origin of structure in the Universe

The early universe is a “laboratory” for testing physics at very high energies, up to a trillion times greater than the energies reached by the Large Hadron Collider. The origin of structure in the universe is deeply tied to this extreme physics, which is imprinted in the primordial ripples seen in the cosmic microwave background (the leftover heat of the Big Bang), and the large scale structure of the universe traced by galaxies. The main purpose of the project is to understand the physics of the early universe, creating innovative algorithms to exploit novel observables, and applying them to next generation CMB data from Planck and large scale structure data, especially DES. The student will be part of the European Research Council Starting Grant Project CosmicDawn. More information about early universe cosmology at UCL can be found here

Contact: Dr Hiranya Peiris (h.peiris AT ucl.ac.uk)


Galaxy formation as a probe of fundamental physics

Galaxies are the fundamental building blocks of the universe. Their internal structure provides critical tests of the dark matter paradigm; they are responsible for the reionisation of the universe; and their distribution on cosmological scales is a key discriminant between competing theories of, for example, dark energy. But extracting the desired information requires a better understanding of the combined dynamics of dark matter, gas and stars in a cosmological setting. As part of an international collaboration, this project will explore the ever-shifting interface between theory, observation and computation. There are opportunities to focus on the galaxy formation physics, on metal enrichment of the intergalactic medium, or on the application of new ideas in these areas to galaxy survey design and exploitation.

Contact: Dr Andrew Pontzen (a.pontzen AT ucl.ac.uk)


Pinning down the properties of gravity on cosmological scales

Powerful probes of the large-scale structure of the Universe are now routinely used to constrain models of dark matter, dark energy, and other 'dark' physics. By combining techniques like the clustering of galaxies, redshift-space distortions, and gravitational lensing by the large-scale structure in co-spatial surveys, we will be able to measure the growth of structures and the geometry of space simultaneously, and thereby improve the constraints on dark physics, as well as test the validity of Einsteinian gravity on large scales. Projects could involve the analysis of data from on-going ground-based surveys such as the Kilo-Degree Survey (KiDS), or the development and testing of new analysis techniques for the forthcoming ESA space mission Euclid.

Contact: Dr Benjamin Joachimi (b.joachimi AT ucl.ac.uk)

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Page last modified on 17 dec 13 08:41 by Serena Viti