We combine optical, X-ray (Einstein and ROSAT) and infrared (IRAS) data to investigate the evolution and spatial distribution of AGN with particular emphasis on the implications for the origin of the diffuse X-ray background. First, we derive the IRAS Seyfert luminosity function to test the continuity of properties between the Seyfert and the QSO population. The QSO luminosity function evolved back to z ~ 0, agrees well with the Seyfert luminosity function. In particular, the similarity of the faint parts of the two luminosity functions, suggests that the optical luminosity function is not severely affected by incompleteness due to reddening. We analyze the clustering properties of the IRAS Seyfert sample in order to probe the AGN clustering evolution. We detect clear clustering (5σ) at scales < 20 h(^-1). Comparing the Seyfert with the QSO clustering results at higher redshifts we find that a comoving model for AGN clustering evolution, where AGN clusters are expanding with the Hubble flow, is probably favoured by the data. Using new faint CCD observations we recalibrate the photometry of the Durham UVX catalogue of Boyle et al. (1990). We show that the luminosity function 'knee' feature claimed by Boyle et al. is not an artefact of photometric errors at faint magnitudes. We evaluate the contribution of Active Galactic Nuclei (AGN) to the X-ray background using this optical luminosity function and evolve it according to Pure Luminosity Evolution models. We estimate that AGN produce around half of the X-ray background at 2 keV. This contribution is consistent with the small scale (arcmin) fluctuations of the X-ray background for both the stable and comoving model of clustering evolution. If a large number of low luminosity AGN with high intrinsic absorption is missed by the optical surveys, AGN could produce all the 2 keV intensity. Although the uncertainty in the estimate of the AGN contribution is high, this work demonstrates, at least, that Pure Luminosity Evolution models are consistent with both the X-ray background intensity and anisotropy constraints. A recent deep ROSAT observation yields a high surface density of X-ray sources (> 100 deg(^-2). Spectroscopic follow up observations show that most of these sources are QSOs. The identified QSOs contribute ~ 30% at 1 keV and therefore this is the lower limit of the AGN contribution to the X-ray background. No other class of sources contributing substantially to the X-ray background has been yet identified.

Blazars are a subclass of active galactic nuclei whose observable characteristics are generated by relativistic jets of high-energy plasma with trajectories closely aligned to the line of sight. This orientation results in extreme observed phenomena, such as ultraluminous emission, high amplitudes of variability, and high degrees of optical linear polarization. Furthermore, blazars are the most common extragalactic sources of γ-ray photons and have been proposed as sources of high-energy neutrinos. Long-timescale monitoring of blazars has revealed relatively quiescent states interspersed with active states featuring dramatic brightening events, with timescales ranging from months to years. New, high-time-resolution observations of blazars are revealing dramatic variability on timescales as short as several minutes, the physical drivers of which are not well understood. In this dissertation, I focus on observational signatures that can potentially identify these mechanisms. To characterize this variability, I combine observations of blazars from many telescopes, obtaining a comprehensive view of events occurring in the jets. Using the Very Long Baseline Array, I investigate moving and quasi-stationary features in the parsec-scale jets of 38 blazars. I find that the flow speeds, orientation, brightness temperatures, and opening angles of the jets in flat-spectrum radio quasars (FSRQs), BL Lacertae type objects (BL Lac objects), and radio galaxies (RGs) are statistically different, with FSRQs having the highest speeds and smallest viewing angles. Focusing on a typical source of each subclass, I characterize the optical variability observed at 2-min cadence (with the Transiting Exoplanet Survey Satellite), at gamma-ray energies (Fermi Large Area Telescope), X-ray energies (NICER, NuSTAR, and Swift satellites), and optical (ground-based instruments, especially, the Perkins telescope), including linear polarization measurements. I find that the minimum timescale of RG variability is longer than those of the FSRQ and BL Lac object, and is likely caused by changes in the accretion disk. In contrast, the variability in the FSRQ and BL Lac object can be associated with shocks, magnetic reconnections, and turbulence in the jet. The unprecedented availability of data, which promises to expand in the future, represents a new phase of observational astronomy that provides valuable information on changes in the jets of blazars.

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.

Studies of central black holes (BHs) in nearby galaxies revealed tight correlation between the BH mass the host galaxy bulge mass, indicating a link between BH and star formation (SF) in the host galaxy. Luminous active galactic nuclei (AGN) are powered by mass accretion onto supermassive BHs. Observations of the AGNs and the SF in their host galaxies are required to understand their relation and how they establish this BH mass-galaxy bulge mass correlation over a wide range of cosmic lookback times. This thesis presents a survey of 24 μm-selected luminous AGN and their host galaxies up to z ~ 3.2. It focuses on the foreground and background broad line (Type-1) and narrow line (Type-2) AGNs of 30 massive galaxy cluster fields with total survey area of 5.2 deg², using the multi-wavelength dataset from the ultraviolet (UV) to far infrared (FIR) from the Local Cluster Substructure Survey. The AGN sample is nearly complete to a 1 mJy flux cutoff at 24 μm, and is optical-spectroscopically identified. With this dataset and the accompanying MMT/Hectospec spectroscopy survey, the properties of AGNs such as BH masses, BH accretion rates, and total luminosities, can be readily determined. Particularly, the Herschel data (100, 160, 250, 350, and 500 μm) sample the FIR peak of sources in our sample, and provide constraints on the star formation rates (SFR) in the host galaxies. For the Type 1 AGN sample, most of the systems are at z > 0.6 with luminosities > 10^45 ergs/s. Out of the 205 Type-1 AGNs, 107 are detected in at least two Herschel bands. We use AGN, stellar, and SF galaxy templates to decompose their spectral energy distributions (SEDs) from the UV to the FIR, and estimate their IR SF luminosities, AGN luminosities, and their host galaxy stellar masses. The SED decomposition reveals that a high level of SF is ubiquitous for our 24 μm-selected Type-1 AGN sample. For sources at z < 1, the stellar components from SED decomposition provide direct constraints on the stellar mass. For sources at z > 1, the BH mass-bulge stellar mass correlation is used for indirect constraints on the stellar mass. We carried out a similar analysis on the 85 Type-2 AGNs and their host galaxies up to z ~ 0.8, out of which 55 are detected in at least two Herschel bands. We reach the same conclusion as for the Type 1 AGN sample. That is, 1) These AGN host galaxies are very massive, and the vast majority of these galaxies have specific star formation rates (SSFR) consistent with those of main-sequence, star-forming galaxies rather than starbursting galaxies; 2) Most of these AGNs accrete at a rate close to 10% of Eddington; 3) We also find a strong correlation between the IR luminosity of the SF component and the AGN total luminosity, for both Type 1 and Type 2 AGNs. However, we show that the correlation could arise just because the BH mass (and hence AGN total luminosity) and the SF are both correlated with the galaxy mass, rather than requiring a causal connection between the observed rates of SF and the nuclear activity.

This thesis is concerned with very high energy γ-ray observations of blazars observable from the southern hemisphere. The data presented were obtained using the recently deployed University of Durham Mark 6 high sensitivity Čerenkov telescope. Chapters 1 and 2 are introductory; the subjects of γ-ray astronomy, extensive air showers, Čerenkov light production, the development of the atmospheric Čerenkov technique and the current status of TeV astronomy are discussed. Chapter 3 introduces the telescopes operated by the University of Durham. The Mark 6 telescope, designed to have a low threshold energy and a high resolution imaging system, is discussed in detail. Chapter 4 presents the calibration and analysis techniques routinely applied to data obtained with the Mark 6 telescope. The chapter concludes with a set of moment parameter selections designed to reject a significant fraction of the cosmic ray cascades, while retaining the majority of γ-rays cascades. These selections have resulted in a 5σ detection of PSR 1706-44. Chapter 5 discusses active galactic nuclei and in particular blazars. Topics included are recent high energy observations; the differences between the radio/X-ray selected BL Lacs and flat spectrum radio quasars; the infrared background; high energy flux variability and γ-ray production mechanisms within these objects. The chapter concludes with a list of possible very high energy γ-ray emitting blazars observable with the Mark 6 Čerenkov telescope. Chapter 6 presents the results from four of these very high-energy γ-ray blazar candidates; PKS 0548-322, PKS 1514-24, PKS 2005-489 and PKS 2155-304. There is no evidence for γ-ray emission from these sources, either in the form of a steady flux or variable activity. Three sigma integral flux upper limits above 300 GeV are produced for these objects and the implications of these observations are discussed. The conclusions are presented in Chapter 7 as well as ideas for future work.

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Thesis (M.Sc.)--York University, 2004. Graduate Programme in Physics and Astronomy. / Typescript. Includes bibliographical references (leaves 86-89). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url%5Fver=Z39.88-2004&res%5Fdat=xri:pqdiss &rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR11775