MSc: What are Spiral Arms?

Master Thesis

Job Code: MSc Spiral Arms

Job Offer from September 28, 2021

Time frame

This M.Sc. project is on offer until Christmas 2021.

Project description

Disk galaxies like our Milky Way are famous for the spiral arms made from stars, gas and dust that thread their galactic disks. While it is easy to visually identify the spiral arms on galaxy photographs or simulation pictures, it is very hard to define *dynamically* what spiral arms are. In other words: On what kinds of orbits are the stars moving, that together create the visual impression of a spiral arm? What creates these spiral arms? And is there a fundamental difference between spiral arms in galaxies with strong central bars and those without a bar?

Different spiral theories suggest different kinematic signatures, but we have no idea which of them applies to the spiral arms in our own Milky Way. Is the famous and still unexplained kinematic substructure in the Galactic disk - which was observed by the Gaia satellite in 2018 - caused by the bar, or dwarf galaxy interactions, or are we maybe seeing the spiral arms? This puzzling question will see its exciting next chapter in 2022 with the 3rd Gaia data release.

Given the complexity of the mechanisms at play in the Milky Way, it is crucial to study them in realistic galaxy simulations. The "Auriga" simulations are a suite of Milky-Way-like disk galaxies with a full cosmological context, and the "Superstar" simulations are a very new high-resolution re-run with 10^8 star particles. This amount of "stars" within a fully self-consistent and realistic galaxy formation history is unprecedented and allows us to understand bar and spiral arm signatures in incredible detail.

Auriga Halo 18 has a prominent central bar and spiral arms. A dynamic study in action-angle space has revealed the expected signatures of the bar - and interesting structures beyond that. The next step would be to perform a similar analysis of the Auriga Halo 6, which has no bar, but strong spiral arms. A comparison between both halos might give insights into the orbital characteristics of spiral arms.

This proposed M.Sc. project... available immediately, as the simulation data, Python code for the data analysis, and the analysis of Halo 18 exist already.

...has a lot of scientific potential, because if we find a dynamic description of spiral arms in action-angle space based on simulations, this would result no doubt in an important publication. extremely timely, as understanding Galactic spiral arms will become even more important with Gaia’s 3rd data release next year. Also, the "Superstars" simulations are so new and cool and need to be studied *now*!

...allows the student to connect not only with scientists at MPA, but also with the international collaborators of the "Superstars" team. With respect to applying for PhD positions this might be very interesting for the student.

...would provide valuable experience including "Python programming", "big data" and "data analysis", which are sought after in industry.

...will definitely be fun, because our 7-person "Superstars" team is so nice! :-)


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