Institute for Astronomy
Institute for Astronomy
Contact us

Milky Way & Local Group PhD Projects

Research projects on offer in our Milky Way & Local Group Galaxies research group.

Probing the stellar and dark matter halos of the Andromeda galaxy

Prof Sergey Koposov

One of the remarkable results in astrophysics of the last 20 years has been the direct observation of the hierarchical nature of galaxy formation through the detection of tens of dwarf galaxies orbiting the Milky Way and stellar streams from multiple disrupted star clusters and dwarf galaxies. These discoveries were enabled by data from photometric surveys of the Milky Way, as well as spectroscopic and astrometric surveys like Gaia.

The study of stars in the stellar halo of the Milky Way has revealed a wealth of information about the galaxies that were accreted. For example, 5 years ago it was learned that most of the inner stellar halo of the Milky Way was contributed by a single galaxy accreted about 10 Gyr ago. In addition to understanding individual accretion events in the halo, the stellar streams produced by disrupted systems allow us to probe the distribution of dark matter in the Milky Way.  Some early results suggest that the Milky Way dark matter halo may be triaxial and is currently deforming due to its interaction with the Large Magellanic Cloud.  While the measurements of the Milky Way have been ongoing successfully, they represent only one galaxy. Our nearest large neighbour, the Andromeda galaxy (M31), is about twice as massive as the Milky Way, but comparatively little is known about its halo. Because it is much further away, studies of M31 have been limited.  There was an imaging PANDAS survey of Andromeda that showed a vast amount of substructure in the M31 halo, but very little spectroscopic data was available for M31, mostly obtained with the Keck telescope. This has completely changed with the arrival of the Dark Energy Spectroscopic Instrument (DESI), which is a spectrograph that can simultaneously obtain 5000 spectra covering a 50 kpc diameter area in a single exposure. We have made some early observations of M31 with DESI, measuring the large stellar stream in M31, but by now DESI has observed significantly more fields, and there is an ongoing program targeting a large fraction of the M31 stellar halo. With the existing and upcoming data, we are approaching a full view of the stellar halo of M31. In some respects, this external view is better than what we have of the Milky Way, as we are restricted to an internal vantage point within the Galaxy.

In this project, you will be working with the exciting new DESI observations of Andromeda, characterising its merger history and measuring the distribution of dark matter in its halo. With this data, we will learn much more about how Andromeda differs from the Milky Way and will better understand galaxy formation processes happening in both systems.

This project will be conducted within the international DESI collaboration and the Milky Way Survey working group.

The project will primarily involve data analysis, with the potential to incorporate numerical simulations.

The key papers:

Dynamics of Non-Equilibrium Galaxies and the Distribution of Dark Matter

Prof Jorge Peñarrubia and Dr Mike Petersen

Understanding the distribution of dark matter in the Milky Way and its satellite galaxies requires accurate dynamical models of their stellar components. However, in a cosmological environment, galaxies are continuously perturbed by mergers, tidal interactions, and the presence of dark matter substructure. As a result, most galaxies are not in dynamical equilibrium — a fact that is often ignored in standard mass-modelling techniques.

This PhD project will develop and apply new dynamical methods that explicitly account for the non-equilibrium nature of galaxies. The student will study:

  • The response of the Milky Way to the gravitational influence of the Large Magellanic Cloud (LMC).
  • The evolution of satellite galaxies orbiting within a clumpy dark matter halo, including perturbations from subhaloes.
  • The internal kinematics of individual dwarf spheroidal galaxies, many of which show signs of tidal disturbance.

The ultimate goal is to obtain improved constraints on the distribution and properties of dark matter in the local Universe.

Data and Methodology

The student will combine state-of-the-art observational datasets with numerical and statistical modelling:

  • Astrometry: Gaia DR3 and later releases
  • Spectroscopy: 4MOST, WEAVE, and complementary follow-up data
  • Photometry: LSST, Roman Space Telescope, and ESA Euclid

They will develop and use:

  • N-body simulations to model galaxy interactions
  • Bayesian inference methods to extract dynamical parameters and quantify uncertainties
  • Novel techniques analyse stellar phase-space structures and non-equilibrium signatures

Training and Skills Development

The student will gain expertise in:

  • Computational astrophysics and high-performance computing
  • Dynamical modelling and gravitational theory
  • Statistical inference and Bayesian methods
  • Analysis of large-scale astrometric and spectroscopic surveys

This project is ideally suited for a student interested in galaxy dynamics, cosmology, and the nature of dark matter. Prior experience in astrophysics, physics, or applied mathematics is beneficial, and familiarity with Python/C/Fortran will be an advantage.

Under the Computational Astrophysics projects, see also:

This article was published on