No description available.

No description available.

No description available.

No description available.

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.

Galactic nuclei are important for studies of galaxy evolution, stellar dynamics and general relativity. Many have Supermassive Black Holes (SMBHs) (with one million to one billion times the mass of the sun) that affect the large scale properties of their hosts. They are also the densest known stellar systems, and produce unique electromagnetic and gravitational wave sources via close encounters between stars and compact objects. For example, stars that wander too close to an SMBH are tidally disrupted, producing a bright flare known as a TDE. This thesis investigates the gas and stellar environments in galactic nuclei. In Chapters 2 and 3, we develop an analytic model for the gas environment around quiescent SMBHs. In the absence of large scale inflows, winds from the local stellar population will supply most of the gas. The gas density on parsec scales depends strongly on the star formation history, and can plausibly vary by four orders of magnitude. In Chapter 3, we use this model to constrain the presence of jets in a large sample of TDE candidates. In Chapter 4 we construct observationally motivated models for the distributions of stars and stellar remnants in our Galactic Center. We then calculate rates of various collisional stellar interactions, including the tidal capture of stars by stellar mass black holes. This process produces ~100 black hole LMXBs in the central parsec of the Galaxy (comparable to the number inferred from recent X-ray studies).

During the close approach of two galaxies in a merger, tidally induced gas inflows can trigger simultaneous black hole accretion which are observed as dual active galactic nuclei (dAGNs). Merger simulations predict that the resulting increased nuclear gas reservoirs will obscure the X-ray emissions from the AGNs. We investigate whether dAGNs in mergers are observed to be more obscured than their isolated counterparts by combining the results of previous radio and optical spectroscopy studies with new Chandra X-ray observations for a sample of 4 dAGN systems in the Stripe 82 field. For the 6 detected components, we find the rest-frame X-ray luminosities range between 39.8 < log LX /erg s-1 < 42.0. The sources have redshifts between 0.04 < z < 0.22 and projected separations between 4.3 and 9.2 kpc, as well as multi-wavelength properties most closely resembling low-luminosity AGNs. However, we determine that the X-ray emissions for 2 of the sources likely has strong contributions from hot interstellar medium, and star-formation and X-ray binaries may contribute to the X-ray luminosities of several sources. We do not find evidence of enhanced obscuration through our analysis of X-ray hardness ratios, optical [O III] emission line luminosities, and mid-infrared luminosities. Therefore, we suggest that the unobscured low-level accretion observed for the AGNs in this sample is driven through stochastic processes rather than the massive gas inflows predicted for a merger-driven scenario.

Thesis (M.Sc.)--York University, 2007. Graduate Programme in Physics and Astronomy. / Typescript. Includes bibliographical references (leaves 67-69) Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR38756

This dissertation addresses the co-evolutionary relationship between central super-massive black holes and host galaxies. This relationship is suggested by observed correlations between black hole mass (M[subscript BH]) and properties of the host galaxy bulge. We first discuss investigation of the relationship between MBH and host galaxy velocity dispersion, [sigma subscript asterisk], for quasars in the Sloan Digital Sky Survey (SDSS). We derive MBH from the broad emission line width and continuum luminosity, and [sigma subscript asterisk] from the width of narrow forbidden emission lines. For redshifts z < 0.5, our results agree with the locally-observed M[subscript BH]- [sigma subscript asterisk] relationship. For 0.5 < z < 1.2, the M[subscript BH]- [sigma subscript asterisk] relationship appears to evolve with redshift in the sense that bulges are too small for their black holes. Part of this apparent trend can be attributed to observational biases, including a Malmquist bias involving the quasar luminosity. Accounting for these biases, we find approximately a factor of two evolution in the M[subscript BH]- [sigma subscript asterisk] relationship between the present and redshift z [approximately equal] 1. The second topic involves a search for the largest velocity dispersion galaxies in the SDSS. Black holes in quasars can have M[subscript BH]exceeding 5 billion M[mass compared to the sun], implying [sigma subscript asterisk] > 500 km s−1 by the local M[subscript BH]- [sigma subscript asterisk] relationship. We present high signal-to-noise HET observations for eight galaxies at redshift z < 0.3 from the SDSS showing large [sigma subscript asterisk] while appearing to be single galaxies in HST images. The maximum velocity dispersion we find is [sigma subscript asterisk] = 444 km s−1, suggesting either that quasar black hole masses are overestimated or that the black hole - bulge relationship changes at high black hole mass. The third topic involves work contributed to co-authored papers, including: (1) evidence for recoiling black holes in SDSS quasars, (2) the [sigma][O III] - [sigma subscript asterisk] relationship in active galactic nuclei (AGN), and (3) accretion disk temperatures and continuum colors in quasars. Lastly, we discuss research in progress, including: (1) possible physical influences on the width of narrow emission lines of SDSS AGN, including the gravitational effect of the black hole, and (2) a search for binary AGN in the SDSS using double-peaked [O III] emission lines. / text

No description available.