Active Galactic Nuclei (AGN) are some of the most extreme objects in the universe. They output copious amounts of energy spanning the entire electromagnetic spectrum. There are many different subclasses of AGN depending on your viewing angle. Blazars, viewing down the relativistic jet, are the most variable class of AGN known. They exhibit extreme variability in all wavelengths on timescales as short as minutes. In this thesis I will consider the extreme faintness of 3C279 with respect to the long-term light curve as well as recent observations of microvariability. I am able to confirm small amplitude events using simultaneous observations from two telescopes and cross correlation analysis. Transitory quasi-periodic oscillations are observed during two of the nights with confirmed microvariability.

Thesis (Ph.D.). / Written for the Dept. of Physics. Title from title page of PDF (viewed 2008/02/12). Includes bibliographical references.

Thesis (Ph.D.)--Michigan State University. Astrophysics and Astronomy, 2008. / Title from PDF t.p. (viewed on July 6, 2009) Includes bibliographical references (p. 137-141). Also issued in print.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 139-146).

When we look throughout the Universe, we can see the stages of galaxy evolution across cosmic time; however there are still many unanswered questions about the details of galaxy evolution. How did galaxies like our Milky Way assemble? Do the first galaxies look different than our own? What makes galaxies stop forming stars? Many of these questions can be addressed by studying the detailed chemistry of gas located in and around galaxies. Absorption lines imprinted on quasar spectra probe this hard-to-see gas within and surrounding galaxies, giving an luminosity-unbiased census of gas from z~0 to the epoch of the most distant quasars. In this thesis, I present two samples of high resolution spectra of quasars obtained from both ground- and space-based observatories to study the evolution of galaxies through their gas-phase absorption lines. The first of the two samples presented in this thesis consists of the 100 quasar sightlines from the XQ-100 legacy survey completed with the X-Shooter spectrograph on the Very Large Telescope in Chile. The XQ-100 survey provides a blind sample of over 350 HI absorption line systems associated with galaxies with column densities 18.8<=logN(HI)<=21.5. Using this sample, I investigated the evolution of neutral gas reservoirs from z~4.5 to z~2.0. I demonstrate that the lower column density sub-damped Lyman alpha systems (with column densities 19.0<=logN(HI)<20.3) contribute ~20% of the HI observed in galaxy gas reservoirs compared to the rarer but high column density damped Lyman alpha systems (DLAs; logN(HI)>=20.3). Furthermore, I show that using the presence of metal lines (particularly MgII absorption) to identify and select absorbing systems can potentially bias the properties of the sample; absorbers selected to contain strong metal line absorbers tend to exclude low metallicity and low HI column density systems. I demonstrate that the systems missed by metal-selected searches can have a significant impact on the study of the cosmic evolution of neutral gas reservoirs. In addition to the HI content, the metal abundances for 13 elements in the 41 DLAs of the XQ-100 sample are presented. In concert with my literature compilation of 280 DLA metal abundance measurements, I studied the dust-corrected [Zn/Fe]. This work emphasizes that near-IR coverage of X-Shooter provides unprecedented access to MgII, CaII and TiII lines (at redshifts 3-4) to provide additional evidence for subsolar [Zn/Fe] ratio in DLAs, a chemical signature that DLAs can be high-redshift dwarf galaxy analogues. Furthermore, the XQ-100 DLA sample consists of several unique systems that probe the effects of environment on the chemical evolution of the Universe, as well as the chemical makeup of the first generations of stars. I demonstrate that DLAs close to their background quasar (within 5000 km/s) with logN(HI)<21.0 show lower [S/H] and [Fe/H] (relative to intervening systems with similar redshift and N(HI)), whilst higher [S/H] and [Si/H] are seen in these proximate systems with logN(HI)>21.0. Contrary to previous studies, DLAs within 10,000 km/s of another DLA show no difference in [alpha/Fe] relative to single DLAs matched in metallicity and redshift. In addition, I present follow-up high-resolution data of J0034+1639, a sightline containing three DLAs, including a metal-poor DLA with [Fe/H]=-2.82 (the third lowest [Fe/H] in DLAs identified to date) at z=4.25. In the latter part of this thesis, I study the circumgalactic medium (CGM) of galaxies that host an active galactic nucleus (AGN). AGN are thought to play a critical role in shaping galaxies, but their effect on the gaseous reservoirs surrounding galaxies is not well studied. I present results from the COS-AGN survey: 19 quasar sightlines that probe the gas surrounding 20 optically-selected AGN host galaxies observed over 65 hours with the Hubble Space Telescope. Absorption lines from a variety of species are measured and compared to a stellar mass and impact parameter matched sample of sightlines through non-AGN galaxies. Amongst the observed species in the COS-AGN sample (HI, CII, SiII, SiIII, CIV, SiIV, NV), only HI shows a high covering fraction whilst many of the metal ions are not detected in individual sightlines. A sightline-by-sightline comparison between COS-AGN and the control sample yields no significant difference in equivalent width distribution. However, stacked spectra of the COS-AGN and control samples show significant enhancements in the equivalent width of both Lya and SiIII at high impact parameters (>164 kpc) by a factor of +0.45+/-0.05 dex and >+0.75 dex respectively. The lack of detections of both high-ionization species near the AGN and strong kinematic offsets between the absorption systemic galaxy redshifts indicates that neither the AGN's ionization nor its outflows are the origin of these differences. Instead, I suggest the observed differences could result from either AGN hosts residing in haloes with intrinsically distinct gas properties, or that their CGM has been affected by a previous event, such as a starburst, which may also have fuelled the nuclear activity. / Graduate

Active galactic nuclei (AGN) ubiquitously show outflows. It is now widely recognized that these outflows are key components in the evolution of super-massive black holes and their host galaxies. As important as these outflows are, we still lack sufficient understanding of their structure and energetics. The majority of the work presented in this thesis involved photoionization modeling of AGN outflows along with analysis of density diagnostics in order to determine the distances and energetics of observed outflows. The main findings of these analyses are that 1) outflows are often at distances of hundreds to thousands of parsecs from the central supermassive black hole and 2) quasars outflows can be sufficiently powerful to provide feedback in galactic evolution scenarios. We also find in some cases that the recombination timescales of metal ions are long compared with the flux variability timescales. The large distances we find provide a challenge to current outflow models. For example, these outflows cannot be connected with an accretion disk surrounding the supermassive black hole as assumed in some models. Furthermore, the outflows may be out of equilibrium as we find in Mrk 509. In this case, a thorough understanding of time-dependent photoionization effects is necessary. In this thesis, I include early steps toward understanding time-dependent photoionization as well as ionization studies of accretion disk winds. The main results of these theoretical studies is that 1) the appearance of multiple ionization components in an outflow can be an artifact of the incorrect assumption that the outflow is in ionization equilibrium and 2) the shielding gas required in accretion-disk-wind models should have a clear signature in UV spectra, but none has been observed to date. / Ph. D.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18080号 / 理博第3958号 / 新制||理||1570(附属図書館) / 30938 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 上田 佳宏, 准教授 岩室 史英, 教授 長田 哲也 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

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京都大学 / 新制・課程博士 / 博士(理学) / 甲第23707号 / 理博第4797号 / 新制||理||1687(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 上田 佳宏, 教授 嶺重 慎, 准教授 岩室 史英 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM