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Using a linear, finite difference hydrodynamic code, we have investigated the stability of gas flow within the spiral arms of disk galaxies. Assuming a shock to be present, we have tested the post-shock stability of the flow in the presence of rapidly varying shear, which is characteristic of the region adjacent to shocks in spiral arms. We did this by carrying out a linearized perturbation analysis on the post-shock flow. The perturbations had a simple plane wave form in the azimuthal direction. We included both radial and circular velocities in the background flow, taking into account gradients in the density and velocity profiles. In this sense our simulations differed from previous local analyses. The region under consideration extended from the shock front to the point at which the velocity becomes supersonic. The method could be classified as `semi-global' in the sense that this region encompasses post-shock flow structure, but is small on a galactic scale. We did not consider self-gravity.
Our results indicated that the flow was linearly stable. Any perturbations induced in the flow died out on a rotation time scale. The addition of self-gravity could presumably alter this result. Our simulations also seemed to indicate that in the presence of radial flow, the destabilizing character of the corotation point was overcome. This was true even in the presence of rigid shock boundary conditions.
Electronic Abstract Submitted to the AAS for Jan 94 meeting at Washington DC.
