Milky Way & Local Group PhD Projects
Research projects on offer in our Milky Way & Local Group Galaxies research group:
Testing the particle-nature of Dark Matter with "dark" microhaloes
The nature of dark matter (DM) is a mystery. The current paradigm assumes that DM is made of massive particles that only interact through gravity (the so-called Cold Dark Matter model). This scenario predicts an astounding number of substructures (N~10^15) within galaxies like the Milky Way, with masses that can be as small as that of the planet Earth. However, these objects are too small to have been able to accrete gas and form stars, thereby remaining "dark" throughout their history.
This project will investigate how DM substructures affect the motion of visible objects using N-body simulations and statistical/Monte-Carlo techniques. Student will model gravitational interactions of microhaloes with binary stars and planetary systems. Models will be applied to against astrometric data from the Gaia mission using Bayesian inference techniques.
Quantifying Photon Dominated Regions with ALMA & JWST
Photodissociation Regions (or PDRs) are the interface between the hot, ionised gas surrounding a massive star and its cooler, molecular surroundings. The shock physics and chemistry in these PDRs are so dynamic that it’s hard to figure out where to start understanding them. PDR models are still quite primitive because we haven’t had access to high resolution observations (spatial *and* spectral) at the relevant wavelength ranges (IR to sub-mm) where the interesting shock chemistry happens (which traces the physics).
In this project, the student will apply for and then lead an ALMA project to quantify the PDR and molecular gas in the Horsehead nebula. This region has been chosen because the ALMA project can act as a good compliment to the
JWST/MIRI Guaranteed time project observing the same target which the student will participate in.
Kinematic complexity and black holes in dense star clusters
Black holes of hundreds to a million solar masses are expected to form in dense star clusters, as a result of ‘fast’ (Portegies Zwart et al. 2004) or ‘slow’ (Giersz et al. 2015) stellar collisional processes. But existing scenarios describe the host clusters only as simple non-rotating, isotropic stellar systems, while all clusters that have been identified so far as promising candidates for harboring the - still elusive - ‘intermediate-mass’ black holes show complex kinematic features (e.g., see Anderson & van der Marel 2010). Nonetheless, the physical origin of this possible nexus between ‘kinematic complexity’ and black holes in collisional systems remains unexplored. The first step of the project will be to construct a novel family of rotating, anisotropic equilibria, defined by a distribution function in phase space which include a central massive black hole. The project will then explore, with the aid of direct N-body simulations, the long-term evolution of such rotating equilibria with a mass spectrum, focusing on the study of the dynamical interactions between the intermediate-mass black hole and the smaller (‘stellar-mass’) ones, which naturally form in dense clusters. Finally, there will be scope to estimate the merger rate of such interactions (e.g., see Haster et al. 2016) and to assess the detectability of the associated gravitational wave emission with LIGO, VIRGO, KAGRA, and, in the future, DECIGO and LISA (e.g., see Amaro Seoane 2018). For additional background and references, see Varri et al. 2018 (Sections 9, 10).
Low Mass Stellar Systems at the Star Cluster-Dwarf Galaxy Divide
The nature and origin of small stellar systems with ~10,000-100,000 solar luminosities and half-light radii of less than a few tens of parsecs presents a particular puzzle. Are these examples of the tiniest dwarf galaxies or unusually-extended star clusters? Either way, these enigmatic systems are likely to hold many clues into the nature of dark matter and the modes of early star formation in the Universe. Dynamical investigations of such objects are usually polarised around a sharp dichotomy: if they are approached as star clusters, they are studied as collisional, dark matter-free systems; if they are treated as dwarf galaxies, they are considered as collisionless and dark matter-dominated. But how many stellar systems actually fall into the regime at the interface between collisional and collisionless dynamics, and the implications for their dark matter content is hard to pin down. A PhD student is sought to lead an observational study into the detailed properties of a sample of these systems residing throughout the Local Group, including several recently-uncovered examples in the halos of M31 and NGC6822. The project will involve establishing star formation histories from deep HST and JWST data and measuring internal kinematics with facilities such as MUSE and WEAVE.
The VLT-MOONS Galactic survey: towards a complete chemo-dynamical characterisation inner bulge and bar
The understanding of galaxy formation and evolution is one of the fundamental goals of modern astronomical research. The Milky Way offers a one-of-a-kind opportunity to investigate the formation of a prototypical disc galaxy by looking at the individual ages, chemical abundances, and orbital movements of its stars. In recent years, we have witnessed remarkable progress towards characterising the stellar populations of the Milky Way thanks to large-scale spectroscopic surveys. However, the innermost regions of the Galaxy have remained mostly unreachable to them due to the very large amounts of dust obscuration. This presents a tremendous limitation, as simulations show us that the properties of the central, in-plane regions of disc galaxies hold unique fingerprints of the role that different processes such as dynamical instabilities, hierarchical merging, and dissipative collapse played across the history of the entire galaxy.
In this project, the student will join the leading team of the VLT-MOONS Galactic Survey. The student will work on the development of tools to derive radial velocities, stellar parameters and abundances for millions of stars to be observed with MOONS during its lifetime. The student will participate closely on the design and preparation of the survey, the analysis of commissioning data, science verification, and have a leading role in the analysis the first year of the GTO survey observations. A fraction of the time can be dedicated to the analysis of state-of-the-art simulations of bulge formation and VLT-MUSE observations of nearby bulges, in order to place the forthcoming MOONS results in a general context of bulge formation.
Under the Galaxy Formation & Evolution projects, see also:
- Galaxy Archaeology with the Subaru Near Field Cosmology Survey Annette Ferguson