Galactic astronomy, which studies of our Milky Way Galaxy, is experiencing a revolutionary increase in available data. These surveys are mapping the positions, motions, and properties (e.g. age and composition, which tell us when and where a star was born) of Milky Way stars. This allows us to reveal the structure, dynamics and history of our Milky Way, and infer how disc/spiral galaxies work in general. At the centre of this effort is the Gaia satellite mission, which is mapping the positions and motions of more than a billion stars in an area covering a whole quadrant of the Milky Way. To illustrate this progress: the predecessor of Gaia, Hipparcos, mapped about 100k stars in a region that covers only about one 50th of our distance to the Galactic Centre. In short, right now we can for the first time really map a major part of our galaxy. In addition, ground-based follow-up missions are taking millions of stellar spectra to help us get very precise elemental compositions and parameters for a subset of these stars.
This flood of data requires a lot of models to understand what we are measuring. The MSSL/UCL galaxy group has unique competence in these models and their use in interpreting the data. We have experience in simulations, analytical modelling, and Bayesian/machine learning inference. With these we can map the dark matter content of the Milky Way, constrain the nature of dark matter by mapping the resonances of the Galactic bar in the disc, and build chemo-dynamical models that explore the history of the Milky Way, e.g. for mergers. Particular innovations that this group has pioneered are unbiased stellar distances and parameters. These have allowed us to constrain models for the slowing of the Milky Way’s galactic bar, which have for the first time provided strong evidence for the present inertial mass of dark matter in the Galactic halo; further the first measurement of radial migration, the determination of the solar motion (I.e. where we are moving), and explorations of the warp in the Milky Way disc. In the past years, the research has focused on mostly stellar motions alone, but similar to the use of Hipparcos data, we can expect that in the next years, the focus will shift to combining chemistry with stellar motions.
The focus of the project is on making use of the combined chemical and kinematic data from these missions. The project is to refine existing chemo-dynamical models for the Milky Way by directly challenging them with the new data. The first background models can be used to explore the migration of stars in the Galactic disc and then use those (consistent models) to map the gravitational potential of the Milky Way and (by comparison) map out the dark matter content of the Galaxy. As we found in the past years, these models need to be modified by the expected perturbation from the Milky Way’s galactic bar and spiral arms, which create resonances in the Galactic disc that can be quantified by stream-like structures observed in the stellar motions in the disc. A particular focus is on exploring the interaction of these structures: so far the (slowing) galactic bar, and radial migration of stars driven mainly by the spiral patterns have been modelled separately. However, we know that the bar’s presence will affect the spiral patterns in the Milky Way, imposing limitations on their effects on the Galactic disc, as well as their effects are altered by the superposition of different resonances created by the coexisting patterns. As a benefit, we will obtain i) corrected maps of the Galactic potential, ii) independent constraints from the resonant structure, iii) an improved history of the Galactic disc and origin of the Sun, iv) more precise information on the nature of dark matter residing in the Galaxy.
To achieve this, we use tailored N-body simulations, analytical models, and advanced data analysis. Depending on the skills and preferences of the student, the project can be taken more in a direction of data analysis, refining the stellar parameters, to more theory-dominated studies of resonant dynamics in the disc, or more balanced combinations of both.
Desired Knowledge and Skills
- Undergraduate studies in physics, astrophysics, or related fields
- Strong analytical skills, programming skills desirable (but not required)
For details of how to apply please refer to our website: PhD Opportunities | UCL Department of Space and Climate Physics - UCL – University College London.
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