Michael Hayden

Research

I work on Galactic Archaeology, which is the study of the structure, formation, and evolution of the Milky Way. I study the stars and stellar populations of the Galaxy. Stars contain the chemical imprint of the gas cloud from which they formed, acting as our fossil record of the Milky Way and allowing us to trace back the history of the Galaxy through time. I use large-scale spectroscopic surveys which take spectra of millions of stars throughout the Galaxy to map out its chemodynamic structure and model how the Galaxy has evolved to what we observe today.

Abundance ratios of different elements are key diagnostics to unravelling the history of the Galaxy. This is because different elements are produced from different sources: supernovae, merging neutron stars, and at the end of the life of solar type stars. All of these processes occur on different timescales, so measuring the abundance of different elements can allow us trace the history of the Galaxy even without an age estimate for a star. I made the first complete map of the chemical structure of the disk, from the bulge out to the edge of the disk, comparing how the fraction of alpha elements and overall metallicity varies with location in the Galaxy. These kinds of studies allow us to understand how star formation has proceeded in the Milky Way, and how important different dynamical processes such as radial migration are important in redistributing stars throughout the Galaxy.

I'm currently focused on estimating ages for as many stars as possible throughout the Galaxy. We have found that ages can be directly determined from a stars chemical abundances , allowing us to measure accurate ages for nearly every star observed in spectroscopic surveys. This will give us an unprecedented picture of not only the current structure of the Galaxy, but how it has changed with time.

One other aspect of my research is comparing the Milky Way to external galaxies and simulations. While we can observe individual stars in the Milky Way, which is often not possible in external galaxies, it is still only one Galaxy among countless others. It is important to place the Milky Way in the context of other galaxies to help inform our knowledge and understanding of galaxy evolution in general. I am working on several projects comparing the Milky Way to galaxies of similar mass with MUSE, attempting to map the chemical structure of other galactic disks in a similar manner to what I have done with the Milky Way. I am also comparing observations of the Milky Way to simulations, using machine learning techniques to best identify Milky Way analogues and determine what evolutionary histories commonly lead to Milky Way type galaxies.

CV

Publications

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Elements

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