Dynamical evolution in galactic disks

Astronomy and Astrophysics – Astrophysics

Scientific paper

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Disk Galaxies, Galactic Evolution, Galactic Structure, Gravitational Effects, Gravitational Fields, Spiral Galaxies, Cooling, Gas Heating, Molecular Clouds, Perturbation Theory, Radial Velocity, Stellar Evolution

Scientific paper

An expression is derived for changes induced in the phase-space distribution function when a galactic disk's dynamical structure is changed by fluctuations in its gravitational potential field. The changes are found to be second-order in the perturbing potential, and of the form of a diffusion in phase space. This result is evaluated for the case of a model transient spiral. The radial velocity dispersion of the stars increases in response to a steady sequence of perturbations as t to the 1/2-power for low velocity stars, declining to t to the 1/5-power as the radial excursions of stars become large by comparison with the spirals' spatial wavelength. The present predictions are in agreement with the age/velocity dispersion relation observed in N-body experiments. It is concluded that recurrent transient spirals naturally account for the velocity-dispersion relation observed for the solar neighborhood stars.

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