University of Oulu

Investigating resonance detection methods in disc galaxies

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Author: Mahmoudi Kouch, Pouya1
Organizations: 1University of Oulu, Faculty of Science, Astronomy
Format: ebook
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 14.3 MB)
Pages: 160
Persistent link:
Language: English
Published: Oulu : P. Mahmoudi Kouch, 2020
Publish Date: 2020-05-25
Thesis type: Master's thesis
Tutor: Comerón Limbourg, Sébastien
Reviewer: Salo, Heikki
Comerón Limbourg, Sébastien


In this thesis the reliability of the Font-Beckman (FB) method in locating resonances in disc galaxies is investigated. In the first section of this thesis a general overview about galaxies is provided before moving on to the more specific topics. The literature review heavily focuses on resonance detection methods in disc galaxies, where a number them is used for comparisons with the FB method. The FB method attempts to locate resonances of a disc galaxy by finding zeros in its residual velocity map, which is a map of the galaxy’s non-circular line-of-sight velocity. These zeros are then counted and averaged radially; if a radius shows a clear peak in the number of these zeros, then it is taken as a FB resonance radius. The FB method was fully re-coded for the purposes of this thesis and is put to test in various ways, resulting in a lot of findings although only the main ones are mentioned in this abstract for brevity. The FB method’s reliability is tested via two approaches. The first approach is a simulation-based comparison, in which galaxies with theoretically-known resonances are simulated (using Wada simulations) and the FB method is applied to them. This allows for a direct comparison between FB and theoretical resonances. The main finding is that the FB method can reliably locate outer Lindblad resonances (success rate of 84%±16%), somewhat reliably locate inner Lindblad resonances (47%±27%) as well as inner 4:1 resonances (43%±16%), while it struggles to successfully locate the corotation resonances (17%±17%), which contradicts Font-Beckman’s claim that their method can reliably find corotation resonances. The simulated galaxies were coded such that some of the galactic parameters were adjustable, which allowed us to discover that the FB method works best when the inclination of the galaxy is around 45° as well as other minor findings. The second approach is based on a number of Monte Carlo simulations, where the results from the FB method’s application to real galaxies are used. A number of random resonances are generated and then compared to a number of RI (resonance indicator: a method that detects resonances) resonances. Simultaneously, the FB resonances are compared to the same RI resonances. If FB resonances correlate more closely with the RI resonances as compared to the random resonances with the RI resonances, then it is a positive sign for the reliability of the FB method. Naturally, this depends on how truly reliable the RI are themselves, which is beyond the scope of this study albeit worthy of further investigation. The RIs used are such methods as Tremaine-Weinberg, simulation-based, surface-brightness truncations, Buta-Zhang, rings, etc. In general, we find that the correlation between FB and RI resonances is weaker in barred galaxies. Furthermore, it is found that FB and RI resonances show the strongest correlation when rings are used as RI. Finally, it is concluded that although the FB method is somewhat successful, it is not perfect and further investigation is welcomed.

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Copyright information: © Pouya Mahmoudi Kouch, 2020. This publication is copyrighted. You may download, display and print it for your own personal use. Commercial use is prohibited.