Mathematics – Logic
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt........25h&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF CALIFORNIA, BERKELEY, 1995.Source: Dissertation Abstracts International, Volume: 57-03, Section: B
Mathematics
Logic
3
Starbursts, Quasars
Scientific paper
This dissertation undertakes a systematic investigation of nonstellar activity and star formation in galactic nuclei. Moderate -resolution optical spectra of exceptionally high quality were obtained for nearly 500 bright, northern galaxies, yielding a rich data base that can be used for a number of statistical studies of nearby galaxies. After decomposition of the stellar and nebular components of the integrated spectra, measurements of spectroscopic parameters are presented for the emission-line nuclei, which are classified according to the dominant excitation mechanism of the line-emitting gas. The first part of the dissertation applies the galaxy survey to three specific problems. These address (1) the fraction of galaxies hosting low-luminosity Seyfert 1 nuclei, (2) the influence of bars in the fueling of active galactic nuclei and star formation in the central regions of galaxies, and (3) the spectroscopic properties of star -forming nuclei, their variation as a function of morphological type, as well as their statistical differences compared to those of sites of star formation located in galaxy disks. The rest of the work focuses on the use of emission lines as diagnostic tools to study the physical conditions in emission-line nuclei, with particular emphasis on understanding the origin of low-ionization nuclear emission-line regions (LINERs). LINERs may be the weakest and most common manifestation of the active galactic nucleus phenomenon, although viable alternatives to this interpretation cannot be excluded at the present time. An analysis of recent ultraviolet and X-ray data on the nucleus of the galaxy M81 yields important insights into the properties of the emission -line regions of this prototypical LINER, providing strong support for a genuine link with "classical" Seyfert nuclei. Less direct evidence for a nonstellar origin of LINERs comes from an extensive comparison between their optical/near -infrared spectra and those predicted from a set of new photoionization models.
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