The narrow line region of active galaxies - I. Nuclear O III profiles.

A parameter scheme based on area measurements is developed which characterizes the width, asymmetry and kurtosis of different parts of each of the high dispersion O III forbidden line profiles presented for 42 Southern Hemisphere active and H II galaxies. A comparison with parameters defined by a cut at constant height indicates that the area parameters are less sensitive to noise, more stable to the effects of poor resolution, and more sensitive to information contained in the base and wings of the profile. The data thus obtained are combined with most of the previously published O III forbidden line profile information to form a large sample of line width, asymmetry and kurtosis measurements for Seyfert galaxies. No correlations are found between forbidden O III line width and either the nuclear nonthermal luminosity, the relative strength of the Broad Line Region, or the ionization and physical state of the Narrow Line Region gas. Previous results suggesting that Seyfert 2 galaxies on average possess broader O III forbidden line profiles than Seyfert 1 galaxies are shown to be a consequence of selection effects.