Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999apj...523..147f&link_type=abstract
The Astrophysical Journal, Volume 523, Issue 1, pp. 147-162.
Astronomy and Astrophysics
Astronomy
18
Galaxies: Individual: Ngc Number: Ngc 2110, Galaxies: Individual: Ngc Number: Ngc 5929, Galaxies: Jets, Galaxies: Seyfert, Ultraviolet: Galaxies, X-Rays: Galaxies
Scientific paper
We present the results of UV and optical Hubble Space Telescope/Faint Object Spectrograph spectroscopy 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 Å), G190H (1570-2310 Å), G400H (3235-4780 Å), and G570H (4570-6820 Å) 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 lambda1549 and C III] lambda1909 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 find that shock velocities 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 (n_0) and magnetic parameter (B_0/n^1/2_0) must be relatively high (n_0>10 cm^-3 B_0/n1/20~=4 muG cm^3/2) for the photoionizing shock models to be viable.
Ferland Gary J.
Ferruit Pierre
Mulchaey John S.
Simpson Chris
Whittle Mark
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