The question as to whether the distribution of radio loudness in active galactic nuclei (AGN) is actually bimodal has been discussed extensively in the literature. Furthermore, there have been claims that radio loudness depends on black hole mass and Eddington ratio. We investigate these claims using the low redshift broad line AGN sample of Greene & Ho 2007, which consists of 8434 objects at z < 0.35 from the Sloan Digital Sky Survey (SDSS) Fourth Data Release. We obtained radio fluxes from the Very Large Array Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) survey for the SDSS AGN. Out of the 8434 SDSS AGN, 846 have radio emission within 4" of the optical counterpart and are considered to be core emission. We also perform a systematic search for extended emission in FIRST that can be positively associated with the optical counterparts and find 51 out of the 846 previously detected core sources have extended emission that must be taken into account when calculating the total radio luminosity. Further, we find an additional 12 objects that have extended radio emission but no detectable radio core and have classic FR II type morphologies. Using these data, the question of radio bimodality and the dependence of radio-loudness on physical parameters are investigated for different subsets of the total sample. We find modest trends in the radio-loud fraction as a function of black hole mass and Eddington ratio, where the fraction of RL AGN increases for the largest black hole mass group and decreases with increasing Eddington ratio. With extended emission taken into account, we find strong evidence for a bimodal distribution in radio-loudness, where the lower radio luminosity core-only sources appear as a population separate from the extended sources with a dividing line at log(R) = 1.75. This dividing line is interesting in that it requires the radio luminosity to be 50 times the optical luminosity, ensuring that these are indeed the most RL AGN, which may have different or extreme physical conditions in their central engines when compared to the more numerous radio quiet AGN in this sample.

Thesis (Ph. D.)--Rutgers University, 2009. / "Graduate Program in Physics and Astronomy." Includes bibliographical references.

The relation between central or mean metallicity and luminosity in elliptical galaxies is a well observed phenomenon. Theoretical explanations proposed for this relation include scenarios in which peak metallicities are determined either by the epoch at which the remaining gas is expelled from the galaxy by supernova-driven winds, or by the efficiency of star formation following a series of mergers by small stellar/gaseous subsystems. These explanations suggest that an investigation of the metallicity-luminosity relation for spiral galaxies might have implications for galaxy formation models and for the origin of SO galaxies. The existing evidence concerning SO's points to a relation between mean metallicity and total luminosity. The problem of measuring metal abundances in the nuclei of spiral galaxies is that the line strength variations due to metallicity changes must be distinguished from those due to a filling in of the lines by the continuum from a young population. This was accomplished by measuring absorption line indices for Mg b and for a CN band at λ3880. Nuclear spectra of twenty ellipticals, obtained with a reticon detector, show these two indices to be well correlated for pure old populations; models including the effects of young stars show a very different trajectory for age effects. A procedure is thus defined for determining the metallicity of the population and the fraction of light coming from the young component, and this procedure is applied to observations of 25 spiral galaxies. A comparison of the results of this analysis with detailed population syntheses for six galaxies confirms the correctness of the procedure. In order to obtain bulge luminosities and bulge-to-disk ratios, photographic plates of twenty-two of the spirals were obtained. This material was digitized and reduced to a series of radial luminosity profiles for each galaxy. A procedure was established for decomposing the profiles into disk and bulge contributions. In addition to the desired gross parameters of the bulge and disk, the inclinations and true bulge flattenings for some of the galaxies are accurately determined. A discussion of the results of this analysis deals with the nature of departures from the exponential fitting function for some disks, a decomposition of the Hubble sequence into quantitative parameters, and the implication of the distribution of true bulge flattenings. The metallicities and luminosities are then combined, and two tests indicate that in spiral galaxies, central metallicity and bulge luminosity follow the same relation seen in ellipticals. The implications of this result are twofold. First, galaxy formation models in which the disk material can affect the processes which determine the central metallicity in the bulge are ruled out. Specifically, it is likely that the disks of spiral galaxies are not undergoing vigorous star formation at the time the bulge ceases forming stars. A picture in which the disk material has not yet accreted on to the galaxy at this time is also quite consistent. A somewhat more straightforward implication comes from a comparison of the results of this study with similar studies of SO galaxies. It is concluded that, aside from the uncertain effects of radial gradients, the evidence is inconsistent with the theory that most SO's were at one time spiral galaxies.

No description available.

No description available.

No description available.

Thesis (Ph. D.)--George Mason University, 2007. / Title from PDF t.p. (viewed Jan. 17, 2008). Thesis director: Shobita Satyapal. Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Physical Sciences. Vita: p. 217. Includes bibliographical references (p. 202-216). Also available in print.

Thesis (Ph.D.)--McMaster University (Canada), 1996. / Source: Dissertation Abstracts International, Volume: 58-06, Section: B, page: 3088. Adviser: W. E. Harris.

Thesis (Ph. D. in Physics)--Vanderbilt University, May 2010. / Title from title screen. Includes bibliographical references.

Thesis (Ph. D.)--University of Hawaii at Manoa, 2004. / Includes bibliographical references (leaves 180-192).