Extended ionized nebulosities in seyfert galaxies

Abstract

Many Seyfert galaxies exhibit extended emission line regions on the hundreds of pc to kpc scale. Three disctinct types of nebulosity are found. The first type represents the classical narrow line region (NLR) and comprises gas with high velocity radial motions which is ionized by a central power law continum source. Outside the NLR is found gas which is apparently kinematically undisturbed by the nuclear activity, and follows normal rotational motions, but is ionized by the same central power law continuum. The third type is HII regions ionized by hot stars; in some cases the rate of formation of massive stars is sufficiently high to qualify as a circumnuclear “starburst”. In this paper, I summarize some recent observations of the first and third types of nebulosity. New high resolution images (obtained in collaboration with C. A. Haniff and M. J. Ward) of the NLR in Seyferts with double or triple radio morphology confirm the relation between radio and [OIII] λ5007 axes. These directions agree to within the measurement errors in many cases. Despite this aligment, much of the line emission is not spatially coindcident with the outer radio lobes. The relationship may reflect preferential escape of ionizing photons along the axis of the disk which collimates the radio ejects. If so, limits on the rate precession of this disk are implied. Long slit spectroscopy by Whittle et al. has velocities of these hgh excitation components confirm that the radio clouds are moving outwards. Some recent studies of star formation regions near Seyfert nuclei arre described.