Mathematics – Logic
Scientific paper
Jun 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009phdt.........3r&link_type=abstract
Proquest Dissertations And Theses 2009. Section 0267, Part 0606 287 pages; [Ph.D. dissertation].Canada: York University (Canada
Mathematics
Logic
Seyfert Galaxies, Galaxy Interactions, Active Galactic Nuclei
Scientific paper
It has been suggested that galaxy interactions may be the principal mechanism responsible for triggering non-thermal activity in galactic nuclei. This thesis investigates the possible role of interactions in the local Universe by searching for evidence of a causal relationship between major interactions and the initiation of activity in Seyfert galaxies using high-quality, multiwavelength imaging data.
The connection between interacting galaxies and Seyferts is explored by comparing the clustering properties of their environments, as quantified by the spatial cross-correlation function amplitude. If a direct evolutionary relationship exists, the objects should be located in environments that are statistically similar. It was previously demonstrated that Seyferts are found in fields comparable to isolated galaxies. The analysis presented in this work reveals that interacting galaxies are preferentially situated in regions consistent with Abell Richness Classes of 0 to 1. The apparent dissimilarity of their environments provides a strong argument against a link between major interactions and Seyfert galaxies. An examination of the photometric and morphological properties of the interacting systems does not uncover any trends that could be associated with the initiation of nuclear activity.
The role of major interactions in triggering low-redshift AGNs is then assessed using near-infrared imagery of a sample of Narrow-Line Seyfert 1 galaxies. It has been postulated that these objects are evolutionarily young AGNs, powered by accretion onto supermassive black holes that are considerably lower in mass than those found in typical broad-line Seyferts. By employing the correlation between black hole mass and host galaxy bulge luminosity, the mean black hole mass, [Special characters omitted.] BH , in solar units for the sample is found to be [left angle bracket]log [Special characters omitted.] ( BH )[right angle bracket] = 7.7 ± 0.1, consistent with typical broad-line Seyferts. Using the correlation between the size of the broad line region and the monochromatic continuum luminosity, the mean mass is [left angle bracket]log ([Special characters omitted.] BH )[right angle bracket] = 6.3 ± 0.2. Possible causes for this discrepancy are examined. Furthermore, no evidence is found for asymmetries or extra stellar components that would indicate NLS1s are young objects.
Taken together, these results clearly indicate that major interactions are not a likely source for the initiation of Seyfert activity in the local Universe.
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