Ionization Structure and Emission Line Intensities of Seyfert Galaxy Nuclei

Author: Shields, Gregory Alan

Year: 1973

Degree: Dissertation (Ph.D.)

Advisor: Oke, J. Beverley

Committee Member: Unknown, Unknown

Option: Astronomy

DOI: 10.7907/DAZ1-4251

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.

The ionizing radiation spectrum, geometry, and chemical abundances of the nuclei of the Seyfert galaxies NGC 1068 and 3C 120 are studied with the aid of detailed computer models. These objects represent opposite extremes of the Seyfert galaxy spectral types, but analysis indicates that they are similar in ionizing radiation and nebular geometry. The quantitative success of the models for the high excitation lines supports the idea that photoionization by a central continuum source is the ionization mechanism. However, the low excitation lines may indicate the importance of another process. The most attractive explanation of the observations of both 3C 120 and NGC 1068 involves ionizing radiation similar to that from a black body at 175,000° K with a radius of about 1 a.u, rather than an exponential or power law continuum. Most of the mass ([...]) is contained in a region of gaseous filaments with densities up to about [...] and a radius near 50 pc, which constitutes the entire emission line region of NGC 1068 and the narrow line region of 3C 120. The broad permitted emission lines of 3C 120 come from an additional region of dense, narrow filaments with velocities up to [...] km s-1 located about a parsec from the continuum source. 3C 120 probably has the abnormally large helium abundance N(He)/N(H) = 0.22, but observations are suggested to test an alternative hypothesis involving X-ray ionization. Important constraints provided by existing radio, infrared, and X-ray observations are discussed, and the importance of ultraviolet measurements is emphasized.

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