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Thesis (Ph. D.)--University of Wisconsin--Madison, 1972. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

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We present near-infrared images of nearly 100 host galaxies of Active Galactic Nuclei (AGN). Our quasar sample is comprised of the 50 quasars from the Palomar Green Bright Quasar Survey with redshifts z ≤ 0.3. We have restricted the redshift range to ensure adequate spatial resolution, galaxy detectability, and minimal distance-dependent effects, while still giving a large sample of objects. For lower-luminosity AGN we have chosen to image the CfA Seyfert sample. This sample is composed of 48 Seyferts, roughly equally divided among types 1, 1.5-1.9, and 2. This sample was spectroscopically selected, and, therefore, is not biased towards Seyferts with significant star formation. Taken together, these samples allow a statistical look at the continuity of host galaxy properties over a factor of 10,000 in nuclear luminosity. We find the near-infrared light to be a good tracer of luminous mass in these galaxies. The Seyferts are found in galaxies of type S0 to Sc. The radio quiet quasars live in similar kinds of galaxies spanning the same range of mass centered around L*. However, for the most luminous quasars, there is a correlation between the minimum host galaxy mass and the luminosity of the active nucleus. Radio-loud quasars are generally found in hosts more massive than an L* galaxy. We also detect a population of low mass host galaxies with very low luminosity Seyfert nuclei. The low luminosity quasars and the Seyferts both tend to lie in host galaxies seen preferentially face-on, which suggests there is a substantial amount of obscuration coplanar with the galaxian disk. The obscuration must be geometrically thick (thickness-to-radius ∼ 1) and must cover a significant fraction of the narrow line region (r >100 pc). We have examined our images for signs of perturbations that could drive fuel toward the galaxy nucleus, but there are none we can identify at a significant level. The critical element for fueling is evidently not reflected clearly in the large scale distribution of luminous mass in the galaxy. We also present an infrared image of the jet of 3C 273 and compare it to optical and radio images from the literature.

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The efficiency of the Bowen fluorescence mechanism in models of planetary nebulae and Seyfert galaxy nuclei has been calculated by solving the equation of transfer for He II Ly -o( and the Bowen lines using the Feautrier method. The calculated efficiencies, which do not show significant differences between planetary nebulae and Seyfert galaxies, range from about 40% to 50% for realistic models. These values are somewhat higher than recent empirical determinations of Bowen conversion in planetary nebulae. Certain discrepancies between theoretical and observed line ratios are noted, however, which make the comparison with observation ambiguous. The efficiencies are shown to be rather insensitive to changes in various parameters. It is also noted that observations do not necessarily show that the Bowen lines are systematically weaker in Seyfert galaxy nuclei than in planetary nebulae.

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Recent research has lead to the possible discovery of a new class of gamma-ray emitting ac- tive galactic nuclei (AGN). These objects – the very radio-loud narrow-line Seyfert 1 galaxies (NLSy1s)– demonstrate observational features suggesting that they are similar to blazars. One of the key characteristics of blazars is the presence of high-amplitude optical microvariability. While this phenomenon has been investigated in individual objects, no study of the intra-night variability of radio-loud NLSy1s as a class has previously been available. This dissertation presents a sys- tematic search for optical variability in a sample of 33 radio-loud NLSy1s. It was found that 26 objects demonstrated microvariations. However, only 9 objects did so with duty cycles comparable to blazars, and only 7 of these 9 objects — J0706+3901, J0849+5108, J0948+0022, J1246+0238, PKS 1502+036, J1644+2619, and IRAS 20181-2244 — demonstrated microvariability at compa- rable amplitudes. Two objects stand out as exceptional sources. J0849+5108 was found to have a duty cycle of ~90% and was observed to undergo an enormous 4-magnitude optical flare in a two-month time span. The object has not been reported to have undergone such an event since 1975. The second object, J0948+0022, is the class prototype. High cadence data indicates that J0948+0022 has a remarkably rapid doubling time scale of ~40 minutes, and it was seen to vary by over 0.9 magnitudes within an individual night. Attempts to correlate microvariability to radio loudness, gamma-ray loudness, and other parameters were largely unsuccessful. However, it was found that only radio-loud NLSy1s that were detected at gamma-ray energies demonstrated microvariability at blazar-like duty cycles. Additionally, an analysis of the frequency of microvariations at various amplitudes suggests that the sample of radio-loud NLSy1s presented in this study share a parent population identical to low energy peaked BL Lac-type (LBL) blazars. This is in agreement with the work of astronomers such as Abdo et al. 2009, who have created spectral energy distributions for a few radio-loud NLSy1s and found them to resemble those of LBLs. Blazar-like variability was found in multiple objects with radio loudnesses of log(R) < 2, suggesting that even moderately radio-loud NLSy1s may be blazar-like objects.