A Hubble Space Telescope Survey of Extended [O III] λ5007 Å Emission in a Far-Infrared-Selected Sample of Seyfert Galaxies: Results^*

We present the results of a Hubble Space Telescope (HST) survey of extended [O III] emission in a sample of 60 nearby Seyfert galaxies (22 Seyfert 1's and 38 Seyfert 2's), selected by mostly isotropic properties. The comparison between the semimajor axis size of their [O III] emitting regions (R_maj) shows that Seyfert 1's and Seyfert 2's have similar distributions, which seems to contradict unified model predictions. We discuss possible ways to explain this result, which could be due to either observational limitations or the models used for the comparison with our data. We show that Seyfert 1 narrow-line regions (NLRs) are more circular and concentrated than Seyfert 2's, which can be attributed to foreshortening in the former. We find a good correlation between the NLR size and luminosity, following the relation R_maj ∝ L([O III])^{0.33 ± 0.04}, which is flatter than a previous one found for QSOs and Seyfert 2's. We discuss possible reasons for the different results, and their implications to photoionization models. We confirm previous results that show that the [O III] and radio emission are well aligned and also find no correlation between the orientation of the extended [O III] emission and the host galaxy major axis. This agrees with results showing that the torus axis and radio jet are not aligned with the host galaxy rotation axis, indicating that the orientation of the gas in the torus, and not the spin of the black hole, determines the orientation of the accretion disk, and consequently, the orientation of the radio jet.