Niklas Falstad will present his master's thesis entitled "Gravitational Instability of Two-Component Galactic Discs".

Supervisor/examiner: Alessandro Romeo

Opponent: Annika Franeck

Abstract

The gravitational instability of galactic discs has been investigated for over 50 years, and several stability criteria have been proposed. A common approach is to consider a two-component disc of stars and gas, where both components are treated as fluids. A more realistic, but mathematically more complex, approach is to treat the stellar component as collisionless, using kinetic theory. In recent years, sensitive and high-resolution observations of nearby galaxies have provided data of unprecedented value. It is then important to assess the accuracy of those stability criteria when used for analysing such data. We therefore perform a rigorous comparative analysis, using a full set of stability diagnostics, of stability criteria based on the two approaches mentioned above. We find that the fluid-fluid stability criterion has almost the same accuracy as the kinetic-fluid criterion. We also find that, except in a small region of the parameter plane, the fluid-fluid approximation can be reliably used for finding the wavenumber at which the disc is most unstable. Under certain conditions, the contributions of stars and gas to the gravitational instability of the disc can decouple. We find that these conditions only change slightly when using the fluid-fluid approximation.