Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 1975
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1975apj...197....5s&link_type=abstract
Astrophysical Journal, vol. 197, Apr. 1, 1975, pt. 1, p. 5-16.
Astronomy and Astrophysics
Astronomy
106
Astronomical Photometry, Emission Spectra, Galactic Nuclei, Line Spectra, Seyfert Galaxies, Abundance, Continuous Spectra, Diffuse Radiation, Electrophotometry, Forbidden Bands, Ionizing Radiation, Nonthermal Radiation, Photoionization, Radio Sources (Astronomy), Time Dependence
Scientific paper
Photoelectric observations are reported for the nucleus of NGC 1068, and an analysis of the emission-line intensities is presented. The line intensities are found to indicate a filamentary geometry characterized by two densities, and a UV continuum sufficient to ionize the emission-line region is exponentially extrapolated from the optical nonthermal continuum. Detailed models are constructed, which attribute many of the observed line intensities to steady-state photoionization, and a time-dependent model is used to show that strong O II and S II emissions can result from time-dependent ionization due to continuum variability or the motion of photoionized gas into shadows of condensations. Chemical abundances are estimated, and a high nitrogen abundance is found, which is similar to the value of normal galactic nuclei. The results support the hypothesis that the emission-line region of NGC 1068 is ionized by UV radiation rather than by cloud collisions.
Oke Bev J.
Shields Gregory A.
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