We have used the TAURUS technique to study the morphology and velocity field of spatially extended emission–line gas in a number of active galaxies. This paper describes our results for NGC 1275 and NGC 4151. The emission line maps of NGC 1275 are the first scientific data from the new 4.2-m William Herschel Telescope, and show that the morphology of the foreground galaxy falling into the Perseus cluster bears a close relationship to that of NGC 1275 itself, implying that the two galaxies are physically associated.
In the case of NGC 4151, we find the emission line region is elongated along the same axis as the nuclear radio source. This cannot be due to emission-line gas being accelerated by radio ejecta, since the emission-line gas rotates with the galactic disk. We suggest that the emission-line gas is being ionized by a highly anisotropic nuclear continuum source, UV photons escaping from the nucleus preferentially along the radio axis.