PROFILES OF EMISSION-LINES IN ACTIVE GALACTIC NUCLEI .4. ANALYSIS OF A LOW-IONIZATION LINE-PROFILE SAMPLE

A sample of high-resolution AGN narrow spectral line profiles is statistically analysed. Lines included are narrow H-alpha and H-beta, [N II] lambda-6583, [S II] lambda-lambda-6717, 6731, [O III] lambda-5007 and [O I] lambda-6300. Although not very large, differences in width and shape between these lines, seen in the same object, are found to be significant. The range spanned by these differences is the same in Seyfert 1 (Sy 1), Seyfert 2 (Sy 2) and LINER objects. Width and shape profile parameters show systematic dependences with ionization potential and critical density of each forbidden emission fine. These dependences are significantly different in nature between the Sy 1 and 2 classes. In Sy 1, there is clear evidence that regions with larger internal velocities emit preferentially lines of higher ionization conditions. There is also evidence that regions of higher electron density are associated with larger internal velocities. There is marginal evidence that the linewidths of forbidden lines in Sy 1 objects correlate better with critical density than with ionization potential. Sy 2 objects, on the contrary, do not show the same correlations of linewidths and shape with ionization conditions. In a particular object, forbidden fines of higher ionization can be wider or narrower than fines of low ionization. The results indicate that in Sy 1 objects the central ionization source plays a fundamental role in shaping the narrow-line region structure. The same is not necessarily true in Sy 2 galaxies, in which the narrow-line region fine profiles seem to depend on other factors besides the central location of the ionization source.