1998ApJ...508..657M

We have performed a careful decomposition of the broad Hα line profile of the bright, nearby Seyfert 1.5 galaxy NGC 4151 into multiple line-of-sight velocity components, in order to understand its polarization structure. Using the Stokes fluxes, QxF and UxF, we then extracted the polarization properties of each fitted component. Assuming a simple scattering geometry, we can associate several components of the broad-line profile with specific large-scale morphological structures in the host galaxy, such as the radio jet, the central bar, and the dynamical axis. This implies that the broad-line region (BLR) of NGC 4151 is scattered along preferential axes defined by these structures, and suggests the existence of bulk flows along these directions. We propose that NGC 4151 is the result of a merger event. This provides a natural mechanism for coupling the BLR to the host galaxy, for example by streaming of material along the bar from the surrounding regions to the nucleus.