| Abstract | Context: .Spatially resolved emission-line spectroscopy is a powerful tool for determining the physical conditions in the narrow-line region (NLR) of active galactic nuclei (AGNs). We recently used optical long-slit spectroscopy to study the NLRs of a sample of six Seyfert-2 galaxies. We have shown that such an approach, in comparison to the commonly used [O III] narrow-band imaging alone, allows us to probe the size of the NLR in terms of AGN photoionisation. Moreover, several physical parameters of the NLR can be directly accessed.
Aims: .We here apply the same methods to study the NLR of six Seyfert-1 galaxies and compare our results to those of Seyfert-2 galaxies.
Methods: .We employ diagnostically valuable emission-line ratios to determine the physical properties of the NLR, including the core values and radial dependencies of density, ionisation parameter, and reddening. Tracking the radial change of emission-line ratios in diagnostic diagrams allows us to measure the transition between AGN-like and H II-like line excitation, and thus to measure the size of the NLR.
Results: .In the diagnostic diagrams, we find a transition between line ratios falling in the AGN regime and those typical of H II regions in two Seyfert-1 galaxies, thereby determining the size of the NLR. The central electron temperature and ionisation parameter are, in general, higher in type-1 Seyferts than in type 2s. In almost all cases, both electron density and ionisation parameter decrease with radius and the decrease is faster in Seyfert-1 galaxies than in Sy 2s. In several objects, the gaseous velocity distribution is characteristic of rotational motion in an (inclined) emission-line disk in the centre. We give estimates of the black-hole masses and discuss our findings in detail for each object.
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