The evolution of pitch angles of spiral arms

In spiral galaxies, the pitch angle, α, of the spiral arms is often proposed as a discriminator between theories for the formation of the spiral structure. In Lin–Shu density wave theory, α stays constant in time, being simply a property of the underlying galaxy. In other theories (e.g. tidal intera...

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Bibliographic Details
Published in:Monthly notices of the Royal Astronomical Society 2019-11, Vol.490 (1), p.1470-1473
Main Authors: Pringle, J E, Dobbs, C L
Format: Article
Language:English
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Summary:In spiral galaxies, the pitch angle, α, of the spiral arms is often proposed as a discriminator between theories for the formation of the spiral structure. In Lin–Shu density wave theory, α stays constant in time, being simply a property of the underlying galaxy. In other theories (e.g. tidal interaction, and self-gravity), it is expected that the arms wind up in time, so that to a first approximation $\cot \alpha \propto t$. For these theories, it would be expected that a sample of galaxies observed at random times should show a uniform distribution of $\cot \alpha$. We show that a recent set of measurements of spiral pitch angles (Yu & Ho) is broadly consistent with this expectation.
ISSN:0035-8711
1365-2966
DOI:10.1093/mnras/stz2694