Vertical extensions of galactic spiral arms
Abstract
The vertical structure of the large scale galactic shock along spiral arms is studied in order to understand the extended features or the wings of spiral arms observed by Kepner (1970) and recently checked by Soukup (1979). Numerical calculations of twodimensional gas flow were performed for two models of the gas. The results show that the shock front, standing perfectly perpendicular to the galactic plane, extends impressively above the scale height of the interstellar gas. In the extreme case of isothermal gas, the shock solution exists at any distance from the plane. In a realistic model in which the kinetic temperature of the gas is stratified, increasing with height, the shock can extend up to 700 pc. For both models, although the velocity component perpendicular to the galactic plane is small, the solutions corresponding to layered onedimensional flow contain no shocks at such heights. In order to study the geometry of the shock front and the flow pattern near it, a simplified model is adopted, in which the Coriolis force is neglected. However, estimates show that including it will enhance the shock strength. The compression at the shock front makes the gas observable at high latitudes.
 Publication:

The Astrophysical Journal
 Pub Date:
 June 1981
 DOI:
 10.1086/158935
 Bibcode:
 1981ApJ...246..376S
 Keywords:

 Galactic Structure;
 Gas Flow;
 Hydrodynamic Equations;
 Interstellar Gas;
 Shock Waves;
 Spiral Galaxies;
 Computational Fluid Dynamics;
 Coriolis Effect;
 Flow Geometry;
 Flow Velocity;
 Gas Temperature;
 Gravitational Effects;
 Ideal Gas;
 Mathematical Models;
 Shock Fronts;
 Three Dimensional Flow;
 Time Dependence;
 Two Dimensional Flow;
 Astrophysics