GalaHAD: Galaxy Formation With High Accuracy Dynamics

Large star-forming disc galaxies like the Milky Way are some of the most striking and beautiful objects in the Universe, often characterised by their breathtaking spiral arms. Understanding how these fascinating systems arranged themselves into their present state is one of the central aims of modern astrophysics. In my proposed research I will create and analyse simulations with unprecedented resolution within the larger cosmological environment in order to understand how the formation of our Galaxy unfolded.

Our home, the Milky Way galaxy, contains about 100 billion stars. The majority of these stars are in the middle of a large "halo" of dark matter, the crucibles in which galaxies are forged. These haloes are connected to the large-scale filamentary structure of the Universe, dubbed the Cosmic Web, from which haloes acquire gas and smaller galaxies known as satellites. Galaxies grow by accreting this material from their haloes over more than 13 billion years, transforming gas into stars which then move around in response to many complex, highly dynamical processes like gas accretion, mergers and spiral arms. We cannot observe this evolution directly, but astronomers are now able to measure the locations, chemical composition, motions, and ages for a large number of stars to a high degree of accuracy. This "fossil record" information provides vital clues to the birth conditions of stars, which can be very different depending on their origin and age, and how they evolved over Cosmic time. By mapping out this information for many stars, astronomers can piece together how galaxies like the Milky Way formed like a cosmic jigsaw.

The complexity of this great challenge demands sophisticated theoretical models to interpret these observations - the final snapshot in our Cosmic story. However, it is now an enormous challenge for simulations to model both the larger cosmological environment and the central spiral galaxy at the high level of detail necessary to resolve the intricate Galactic structure and its stellar populations that telescopes are now seeing. To get around this roadblock, I will employ new modelling techniques to dramatically enhance the resolution of the stellar and dark matter components of the galaxy to unprecedented levels. These simulations will resolve detailed, highly dynamical structures that were previously inaccessible, and will allow us to follow the many complex physical processes that have occurred since the Big Bang in more detail than ever before. In particular, we will learn how our beautiful spiral arms formed, how they shuffled stars around our Galaxy over Cosmic time, and how epic galaxy collisions that occurred in the ancient Milky Way shaped how it looks today. Additionally, these simulations will open a new window into the formation of very small, low-mass galaxies that lurk in the surroundings of the Milky Way, pushing our current knowledge to new horizons.

Observations require these simulations for their interpretation. Because we currently live in a golden era of large observational surveys which will provide increasing amounts of information, it is essential to carry out this project now in order to maximise our return from these observations. By making mock observations from my simulations, we can compare the simulations directly to observations to provide a holistic view of how the Milky Way formed. We will also learn how the motions of stars can inform us about the nature of the dark matter particle. Answers to these profound questions will greatly benefit mankind's curiosity of the Universe and its mysteries, and inspire future generations of scientists within society. These simulations will be made publicly available and will become a valuable resource for other astronomers, and produce the most detailed images and movies currently available of the origin and formation of our cosmic home.