The Fine Structure of the Spiral‐arms

An explanation for filaments inclined to the galactic plane observed in the next‐inner spiral‐arm is sought in terms of self‐consistent z ‐oscillations. These filaments or „shingles” are observed to be ˜ 1.4 kpc long, 70 pc thick and inclined to the plane by ˜ 12°. In a collisionless axi‐symmetric stellar system we simplify the BOLTZMANN and POISSON equations by assuming a constant density normal to the galactic plane up to z ≈ 200 pc and by assuming a constant radial component of the spatial coordinates. The condition for selfconsistency in the linear approximation results in shingles 1.3 kpc long, inclined to the plane by 17°. The length of the shingles is independent of the radial distance R from the centre and the inclination depends inversely on R as is observed.