Interface region between bars and spirals

Most barred galaxies have a spiral pattern in their outer regions. In several such cases, the outer spiral structure is likely to have a slower pattern speed than the bar. An example is our Galaxy where the bar rotates with a speed of around 40 km/s/kpc while the spiral probably has a rotational speed slower than 30 km/s/kpc. Strong interactions between bar and spiral are expected in the interface region of such systems.
To study these effects, N-body models of galaxies similar to our Galaxy were performed using a 2D log-polar grid. The models were initiated with different bar/spiral configurations to evaluate the stability and degree of interaction depending on pattern speeds and bar length. Test-particle models were used to map the expected velocity distribution for different bar/spiral configurations, while N-body models with an active disk showed the interplay between bar and spiral in the interface region.