Driving a Gaseous Nuclear Spiral Inside the Inner LindBlad Resonance

We model grand-design two-arm spiral structure, recently detected in a number of disc galaxies in the near infrared. We explain the observed continuity between the nuclear and kpc-scale spiral structures and the low arm–interarm contrast, using density-wave theory. We find that nuclear spiral arms form within a range of central mass concentrations and sound speeds in the gas and investigate the allowed parameter space. This revised version was published online in July 2006 with corrections to the Cover Date.