The existence and shapes of dust lanes in galactic bars

Abstract

The flow of gas in and around the bars or ovals of modeled barred galaxies is studied, and it is shown that it is intimately linked to the properties of the periodic orbits. Simulations show that the density of the gas in and around the bar region is slow, except for the center and two narrow lanes which are the loci of shocks. Such shocks form if the x1 periodic orbits have either loops or large curvature values at their apocenters. The form of the shock loci depends on the number of parameters characterizing the bar and disk potential. In order for shocks to be offset from the bar major axis toward its leading side, the x2 and x3 families must not only exist but also cover a sufficient extent along the bar major axis. The existence of offset shock loci of the observed shape puts strict constraints on the values the various model parameters may take. For low values of the bar axial ratio or the bar quadrupole moment the shock loci are curved, with their concave sides towards the bar major axis. Substantial inflow is found in models with strong shocks.