Coherent Stellar Motion in Galactic Spiral Arms by Swing Amplification

Abstract

We perform local $N$-body simulations of disk galaxies and investigate the evolution of spiral arms. We calculate the time autocorrelation of the surface density of spiral arms and find that the typical evolution timescale is described by the epicycle period. We investigate the distribution of the orbital elements of stars and find that in spiral arms the epicycle motions of stars are in phase while the spatial distribution of the guiding center is nearly uniform. These facts clearly show that the phase synchronization of the epicycle motion takes place, which is theoretically predicted by the swing amplification.

arXiv comment13 pages, 10 figures, accepted for publication in ApJ

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• Spirals in galaxies
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• Bar instability and formation timescale across Toomre's $Q$ parameter and central mass concentration: slow bar formation or true stability
• Morphological evolution of disk galaxies and their concentration, asymmetry and clumpiness (CAS) properties in simulations across Toomre's $Q$ parameter