The evolution of pitch angles of spiral arms

Abstract

In spiral galaxies, the pitch angle, $\alpha$, 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, $\alpha$ stays constant in time, being simply a property of the underlying galaxy. In other theories (e.g tidal interaction, 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 2018) is broadly consistent with this expectation.

4 pages, 3 figures, accepted for publication in MNRAS

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• Exciting spiral arms in protoplanetary discs from flybys
• How the bar properties affect the induced spiral structure
• Evolution of the spiral structure of galaxies from the HST COSMOS field
• Galaxy And Mass Assembly: Galaxy Zoo spiral arms and star formation rates
• Less Wound and More Asymmetric: JWST Confirms the Evolution of Spiral Structure in Galaxies at $z\lesssim 3$
• Bar-driven Leading Spiral Arms in a Counter-rotating Dark Matter Halo
• The Observed Age Gradient in the Milky Way -- as a Test for theories of spiral arm structure
• Identification of Intermediate-mass Black Hole Candidates Among a Sample of Sd Galaxies