Astron. Astrophys. Suppl. Ser. 135, 437-466

AGNs with composite spectra

II. Additional data

A.C. Gonçalves - M.-P. Véron-Cetty - P. Véron

Send offprint request: A.C. Gonçalves, anabela@obs-hp.fr

Observatoire de Haute-Provence, CNRS, F-04870 Saint Michel l'Observatoire, France

Received August 11; accepted November 17, 1998

Abstract:

In a previous paper (Véron et al. 1997) we presented medium resolution (3.4 Å FWHM) spectroscopic observations of 15 "transition objects'', selected for having an ambiguous location in the Veilleux & Osterbrock (1987) diagnostic diagrams, and showed that most of them were in fact "composite'', this being due to the simultaneous presence on the slit of both a Seyfert or Liner nucleus and a H II region. Here, we report new spectroscopic observations of 53 emission-line galaxies with a "transition'' spectrum, bringing up to 61 the total number of observed objects in an unbiased sample of 88 "transition objects''. Almost all of the observed galaxies have a "composite" nature, confirming the finding that true "transition'' spectra may not exist at all.

By eliminating "composite objects'' from the diagnostic diagrams, a clear separation between the different classes of nuclear emission-line regions (Seyfert 2s, Liners and H II regions) becomes apparent; by restricting the volume occupied by the different line-emitting regions in the 3-dimensional diagnostic diagrams, we are also restricting the range of possible physical parameters in these regions. There seems to be no continuity between Seyfert 2s and Liners, the two classes occupying distinct volumes in the 3-dimensional space defined by $\lambda 5007/{\rm H}\beta$, $\lambda 6583/{\rm H}\alpha$, and $\lambda 6300/{\rm H}\alpha$.

Key words: galaxies: active -- galaxies: nuclei -- galaxies: seyfert