HUBBLE SPACE TELESCOPZ/FAINT OBJECT SPECTROGRAPH SPECTROSCOPY OF SPATIALLY RESOLVED NARROW-LINE REGIONS IN THE SEYFERT 2 GALAXIES NGC 2110 AND NGC 5929

摘要

We present the results of UV and optical Hubble Space Telescope/Faint Object Spectrograph spectros- copy of bright, extranuclear regions of line emission in the Seyfert galaxies NGC 2110 and NGC 5929. We have obtained spectra of the brightest region of the "nuclear jet" of NGC 2110 (75 pc from the nucleus) and of the southwest emission-line cloud of NGC 5929 (90 pc from the nucleus), in the G130H (1090-1605 A), G190H (1570-2310 A), G400H (3235-4780 A), and G570H (4570-6820 A) configurations. The observed line ratios are compared with the predictions of the two component (matter- and ionization-bounded, MB-IB), central source photoionization models of Binette, Wilson, & Storchi- Bergmann and of the fast, photoionizing ("autoionizing") shock models of Dopita & Sutherland. In both objects, the significant reddening inferred from the Balmer line ratios and/or its uncertainty limit the utility of the ultraviolet carbon lines C iv λ1549 and C III] λ1909 for discrimination between the central source and shock-induced photoionization mechanisms. In NGC 2110, shock + precursor models with a shock velocity of approx=400 km s~(-1) provide a better match to the data than the MB-IB models. However, given the simplifying assumptions made in the latter models, photoionization by a central source cannot be ruled out. We investigate whether photoionizing shocks in the emission-line region of NGC 2110 can power the extended, soft X-ray emission north of the nucleus and find that shock veloci- ties higher than 500 km s~(-1) are required. In NGC 5929, the MB-IB models have problems reproduci