Bars are thought to play a crucial role in the fueling of AGN (see e.g., Mundell et al., in these proceedings and references therein), and as part of a project to investigate this, we have studied the neutral hydrogen structure in the bar of the Seyfert 1.5 galaxy NGC 4151.
High-sensitivity VLA observations have enabled us to image the neutral hydrogen emission from the bar of NGC 4151 in unprecedented detail, and is a continuation of the work by Pedlar et al. (1992).
Figure 1 shows images of integrated neutral hydrogen emission. The large scale emission extends over approximately 20 kpc and the outer part consists of a well-defined two-armed spiral which originates from a fat bar at a radius of about 5 kpc. The bar shows complex structure, including two sharp features which are reminiscent of the shocks seen in many simulations, e.g., Athanassoula (1992). These features appear to join the central 1-kpc ring discovered by Vila-Vilaró et al. (1994), and for which there appears a partial counterpart in neutral hydrogen emission.