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Ionization structure and emission line intensities of Seyfert galaxy nuclei


Shields, Gregory Alan (1973) Ionization structure and emission line intensities of Seyfert galaxy nuclei. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/DAZ1-4251.


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.

Item Type:Thesis (Dissertation (Ph.D.))
Degree Grantor:California Institute of Technology
Major Option:Astronomy
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Oke, J. Beverley
Group:Astronomy Department
Thesis Committee:
  • Unknown, Unknown (chair)
Defense Date:16 October 1972
Record Number:CaltechETD:etd-05272008-083324
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:2167
Deposited By: Imported from ETD-db
Deposited On:27 May 2008
Last Modified:21 Dec 2019 02:22

Thesis Files

PDF (Shields_ga_1973.pdf) - Final Version
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