Hubble Space Telescope/Faint Object Spectrograph Spectroscopy of Spatially Resolved Narrow‐Line Regions in the Seyfert 2 Galaxies NGC 2110 and NGC 5929

Abstract

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 ii nuclear jet ˇˇ 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 G190H (1570¨2310 G400H and G570H (4570¨6820 con—gurations. Ae ), Ae ), (3235¨4780 Ae ), Ae ) 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 (ii autoionizing ˇˇ) shock models of Dopita & Sutherland. In both objects, the signi—cant reddening inferred from the Balmer line ratios and/or its uncertainty limit the utility of the ultraviolet carbon lines C IV j1549 and C III) j1909 for discrimination between the central source and shock-induced photoionization mechanisms. In NGC 2110, shock)precursor models with a shock velocity of ^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 —nd that shock veloci- ties higher than 500 km s~1 are required. In NGC 5929, the MB-IB models have problems reproducing the strengths of the neon lines, while shock)precursor models with a velocity ^300 km s~1 provide a good match to the data. For both galaxies, the emission-line powers and volumes of the ionized gas inferred from observations imply that both the preshock density and magnetic parameter