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
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:
- Cooper et al. (2023) https://ui.adsabs.harvard.edu/abs/2023ApJ...944....1D/abstract
- Dey et al. (2023) https://ui.adsabs.harvard.edu/abs/2023ApJ...944....1D/abstract
- Ibata et al. (2014) https://ui.adsabs.harvard.edu/abs/2014ApJ...780..128I/abstract
Under the Computational Astrophysics projects, see also:
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Instabilities in rotating stellar systems - Prof Steve Tobias, Dr Anna Lisa Varri