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Dissertations / Theses on the topic 'Nuclei-quasars'

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Published: 14 March 2023

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1

Haehnelt, Martin. "Quasars and the formation of galactic nuclei." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319491.

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2

Fernandes, Gomes da Costa Tiago André. "The interaction between quasars and their cosmic environment." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709197.

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3

Schindler, Jan-Torge, Xiaohui Fan, Ian D. McGreer, et al. "The Extremely Luminous Quasar Survey in the SDSS Footprint. I. Infrared-based Candidate Selection." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/627103.

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Studies of the most luminous quasars at high redshift directly probe the evolution of the most massive black holes in the early universe and their connection to massive galaxy formation. However, extremely luminous quasars at high redshift are very rare objects. Only wide-area surveys have a chance to constrain their population. The Sloan Digital Sky Survey (SDSS) has so far provided the most widely adopted measurements of the quasar luminosity function at z > 3. However, a careful re-examination of the SDSS quasar sample revealed that the SDSS quasar selection is in fact missing a significant
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4

Grier, C. J., J. R. Trump, Yue Shen та ін. "The Sloan Digital Sky Survey Reverberation Mapping Project: Hα and Hβ Reverberation Measurements from First-year Spectroscopy and Photometry". IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/627102.

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We present reverberation mapping results from the first year of combined spectroscopic and photometric observations of the Sloan Digital Sky Survey Reverberation Mapping Project. We successfully recover reverberation time delays between the g+i band emission and the broad H beta emission line for a total of 44 quasars, and for the broad Ha emission line in 18 quasars. Time delays are computed using the JAVELIN and CREAM software and the traditional interpolated cross-correlation function (ICCF): using well-defined criteria, we report measurements of 32 H beta and 13 Ha lags with JAVELIN, 42 H
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5

Coatman, Liam. "A near-infrared view of luminous quasars : black hole masses, outflows and hot dust." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/269406.

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Supermassive black holes (BHs) and their host-galaxies are thought to evolve in tandem, with the energy output from the rapidly-accreting BH regulating star formation and the growth of the BH itself. The goal of better understanding this process has led to much work focussing on the properties of quasars at high redshifts, $z\gtrsim 2$, when cosmic star formation and BH accretion both peaked. At these redshifts, however, ground-based statistical studies of the quasar population generally have no access to the rest-frame optical spectral region, which is needed to measure H$\beta$-based BH mass
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6

Constantin, Anca. "Linking the Power Sources of Emission-Line Galaxy Nuclei from the Highest to the Lowest Redshifts." Ohio University / OhioLINK, 2004. http://www.ohiolink.edu/etd/view.cgi?ohiou1097611827.

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7

Down, Emily. "The orientation of accretion disks and jets in quasars." Thesis, University of Oxford, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.572597.

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All massive nearby galaxies, including our own, host supermassive black holes. Active galactic nuclei (AGN) are seen when such black holes accrete, and when they produce powerful jets of synchrotron-emitting plasma, they are termed radio-loud AGN. The close correlation between black hole mass and galaxy bulge mass in elliptical galaxies indicates that AGN feedback may be the key to the regulation of galaxy formation. It is thus necessary to fully understand the structure of AGN, the way that they are fuelled, and their duty cycle, in order to study the feedback processes and get a clear pictur
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8

Bouffet, Romuald. "Evolution de la structure VLBI des sources de l'ICRF : lien entre astrométrie et astrophysique." Thesis, Bordeaux, 2015. http://www.theses.fr/2015BORD0083/document.

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Les Noyaux Actifs de Galaxies (AGN) se situent au centre de galaxies extrêmement lointainesdont la luminosité provient de l’interaction d’un trou noir central supermassif et d’undisque d’accrétion. Il en résulte l’éjection à des vitesses relativistes de jets de matière collimatés.L’interférométrie à très longue base (VLBI) permet, grâce aux très grandes résolutionsatteintes, d’observer finement la structure de ces jets et de déterminer très précisément laposition astrométrique des objets. En raison de leur distance, les AGN ne présentent pas demouvements propres, ce qui les rend idéaux pour la
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9

Blank, Marvin, and Wolfgang J. Duschl. "Viscous time lags between starburst and AGN activity." OXFORD UNIV PRESS, 2016. http://hdl.handle.net/10150/621734.

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There is strong observational evidence indicating a time lag of order of some 100 Myr between the onset of starburst and AGN activity in galaxies. Dynamical time lags have been invoked to explain this. We extend this approach by introducing a viscous time lag the gas additionally needs to flow through the AGN's accretion disc before it reaches the central black hole. Our calculations reproduce the observed time lags and are in accordance with the observed correlation between black hole mass and stellar velocity dispersion.
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10

Draper, Aden R. "Understanding the connection between active galactic nuclei and host star formation through multi-wavelength population synthesis modeling." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45748.

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Supermassive black holes, black holes with masses <106 Msun, are found at the centers of all massive galaxies. These massive black holes grew from smaller seed black holes through accretion events. Accreting black holes are very bright in the radio through very hard X-ray spectral regimes. Due to the location of these accreting black holes at the centers of galaxies, they are referred to as active galactic nuclei (AGN). It is understood that AGN are an important phase of galaxy evolution; however, the role of AGN in massive galaxy formation is very poorly constrained. Here, the unique tool
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11

Krumpe, Mirko. "X-ray and optical properties of X-ray luminous active galactic nuclei." Phd thesis, Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1699/.

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Giacconi et al. (1962) discovered a diffuse cosmic X-ray background with rocket experiments when they searched for lunar X-ray emission. Later satellite missions found a spectral peak in the cosmic X-ray background at ~30 keV. Imaging X-ray satellites such as ROSAT (1990-1999) were able to resolve up to 80% of the background below 2 keV into single point sources, mainly active galaxies. The cosmic X-ray background is the integration of all accreting super-massive (several million solar masses) black holes in the centre of active galaxies over cosmic time. Synthesis models need further populat
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12

Georgakakis, A., M. Salvato, Z. Liu, et al. "X-ray constraints on the fraction of obscured active galactic nuclei at high accretion luminosities." OXFORD UNIV PRESS, 2017. http://hdl.handle.net/10150/625530.

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The wide-area XMM-XXL X-ray survey is used to explore the fraction of obscured active galactic nuclei (AGNs) at high accretion luminosities, L-X(2-10 keV) greater than or similar to 10(44) erg s(-1), and out to redshift z approximate to 1.5. The sample covers an area of about 14 deg(2) and provides constraints on the space density of powerful AGNs over a wide range of neutral hydrogen column densities extending beyond the Compton-thick limit, N-H approximate to 10(24) cm(-2). The fraction of obscured Compton-thin (N-H = 10(22) - 10(24) cm(-2)) AGNs is estimated to be approximate to 0.35 for lu
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13

Pacholczyk, A. G., T. F. Stepinski, and W. R. Stoeger. "Active Galactic Nuclei. III. Accretion Flow in an Externally Supplied Cluster of Black Holes." Steward Observatory, The University of Arizona (Tucson, Arizona), 1988. http://hdl.handle.net/10150/623896.

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This third paper in the series modeling QSOs and AGN as clusters of accreting black holes studies the accretion flow within an externally supplied cluster. Significant radiation will be emitted by the cluster core, but the black holes in the outer halo, where the flow is considered spherically symmetric, will not contribute much to the overall luminosity of the source because of their large velocities relative to the infalling gas, and therefore their small accretion radii. As a result the scenario discussed in Paper I will refer to the cluster cores, rather than to entire clusters. This
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14

Trupia, Denise. "Variability of quasars at the dawn of Universe." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/22212/.

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I buchi neri supermassicci sono onnipresenti al centro della maggior parte delle galassie. Se si verificano eventi di accrescimento, il materiale che cade nel BH si riscalda e diventa molto luminoso: questi oggetti sono chiamati nuclei galattici attivi. A causa della loro elevata luminosità, gli AGN possono essere studiati anche se molto distanti. Un grande enigma dell’astrofisica moderna deriva dalla presenza di buchi neri supermassicci completamente formati ad altissimo redshift (z>6). Questo fatto implica che alcuni di questi oggetti erano simili a quelli che osserviamo al giorno d’oggi qu
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15

Xu, Xinfeng. "How Do Quasars Impact Their Host Galaxies? From the Studies of Quasar Outflows in Absorption and Emission." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/98572.

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``Quasar-mode feedback'' occurs when momentum and energy from the environment of accreting supermassive black hole couple to the host galaxy. One mechanism for such a coupling is by high-velocity (up to $sim$ 0.2c) quasar-driven ionized outflows, appearing as blue-shifted absorption and emission lines in quasar spectra. Given enough energy and momentum, these outflows are capable of affecting the evolution of their host galaxies. This dissertation presents the studies of emission and absorption quasar outflows from different perspectives. (1). By conducting large broad absorption line (BAL)
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16

TURRIZIANI, SARA. "Studying the spectral shape and the X-ray/UV: variability of active galactic nuclei with data from swift and XMM archives." Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2010. http://hdl.handle.net/2108/202327.

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I Nuclei Galattici Attivi (AGN) hanno variazioni di flusso in tutte le bande dello spettro elettromagnetico. In effetti, la variabilità è stata una delle prime proprietà dei quasar ad essere riconosciuta. Sebbene la variabilità giochi un ruolo fondamentale nel dare una stima della grandezza del nucleo centrale degli AGN, la sua origine fisica rimane tuttora sconosciuta. Per spiegare le osservazioni ottiche spno stati proposti diversi meccanismi, ad esempio esplosioni di supernove, cattura di stelle, microlenti gravitazionali o instabilità del disco. La variabilità rapida nella banda X è dunque
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17

Nigro, Cosimo. "Study of Persistent and Flaring Gamma-Ray Emission from Active Galactic Nuclei with the MAGIC Telescopes and Prospects for Future Open Data Formats in Gamma-Ray Astronomy." Doctoral thesis, Humboldt-Universität zu Berlin, 2019. http://dx.doi.org/10.18452/20582.

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Angetrieben durch die Akkretion von Materie in ein super massives Schwarzes Loch in ihrem Zentrum, stellen aktive Galaxien die stärksten und beständigsten Strahlungsquellen im Universum dar. Ihre elektromagnetische Emission kann sich bis in den Gammastrahlenbereich ausbreiten. Das Ziel dieser Arbeit ist, diese Mechanismen und die Orte jenseits der hoch energetischen Emission zu charakterisieren. Dafür werden die Observationen von zwei Aktiven Galaxien im Bereich von hunderten von GeV verwendet, welche mit den Cherenkov Teleskopen MAGIC aufgenommen wurden. Die physikalische Interpretation wird
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18

Gavignaud, Isabelle. "Propriétés statistiques des AGN de faibles luminositées." Phd thesis, Université Paul Sabatier - Toulouse III, 2006. http://tel.archives-ouvertes.fr/tel-00123824.

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Ces dernières années les principaux relevés cosmologiques ont collectés plusieurs dizaines de milliers de spectres de noyaux actifs de galaxies (connus aussi sous l'abréviation anglaise AGN), illustrant ainsi la grande éfficacité des techniques de pré-sélections optiques de candidat AGN. Ils ont ainsi permis une étude statistique détaillée de la population d'AGN.<br />Le revers de ces techniques de pré-sélection est que certaines catégories de la population globale des AGN optiques sont peut-être sous-représentées dans ces échantillons, biaisant notre compréhension actuelle de l'évolution de c
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19

Richards, Gordon Todd. "Intrinsic absorption lines in radio-selected quasars /." 2000. 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:9965146.

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20

Hough, David Hans. "Parsec-Scale Structure in the Nuclei of Double-Lobed Radio Quasars." Thesis, 1986. https://thesis.library.caltech.edu/3434/1/Hough_dh_1986.pdf.

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<p>A complete sample of double-lobed quasars is defined, which is believed to be randomly oriented and which contains many objects with central components accessible to very-long-baseline interferometry (VLSI). The purpose of defining the sample in this way is to facilitate tests of physical models proposed to explain both the compact and extended structures in extragalactic radio sources. Statistical studies of the properties of these objects on the &gt;~ kiloparsec scale are consistent with the assumption of random orientations and the simple relativistic beaming theory.</p> <p>The centra
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21

Chajet, Laura S. "Infrared identification of z > 5.5 quasar candidates /." 2007. 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.

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Thesis (M.Sc.)--York University, 2007. Graduate Programme in Physics and Astronomy.<br>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
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22

Salviander, Sarah Triplett 1971. "Demographics and evolution of super massive black holes in quasars and galaxies." 2008. http://hdl.handle.net/2152/17748.

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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. Fo
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23

BISOGNI, SUSANNA. "The inner structure of Active Galactic Nuclei from spectroscopy of large samples of quasars." Doctoral thesis, 2017. http://hdl.handle.net/2158/1090117.

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Active Galaxies are peculiar galaxies, characterized by non-stellar emission from the central regions of their nuclei (Active Galactic Nuclei, AGN), with luminosities from 10^40 to 10^48 erg s^-1. The energy source for this radiation is the accretion onto a SuperMassive Black Hole (10^6-10^10 Msun ). The discovery that Supermassive Black Holes are present in quiescent galaxies as well as in active ones, along with the finding that AGN activity peaks at z~2-3, suggests that this phase is common to all galaxies and likely influences their evolution. The study of AGN is therefore crucial to unde
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24

VIETRI, GIUSTINA. "The most luminous quasars of the universe: probing the AGN/galaxy co-evolution at its extremes." Doctoral thesis, 2018. http://hdl.handle.net/11573/1051847.

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The systematic, multi-frequency investigation of hyper-luminous quasars shining at the golden epoch of AGN activity offers the unique opportunity of studying the power and the effect of AGN feedback at its extreme. The WISE/SDSS- selected hyper-luminous quasar (WISSH) survey is an extensive multi-band observing program to investigate the role of nuclear activity in SMBH-galaxy self-regulated growth via extended outflows. We found that WISSH AGN are typically powered by highly accreting (0.3-3 Ledd), ten billion solar masses SMBHs, demonstrating that WISSH provides a simple and valuable tool to
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25

Gaspar, Gaia. "Caracterización del entorno de agujeros negros supermasivos en el infrarrojo cercano." Doctoral thesis, 2020. http://hdl.handle.net/11086/22116.

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Tesis (Doctor en Astronomía)--Universidad Nacional de Córdoba, Facultad de Matemática, Astronomía, Física y Computación, 2020.<br>Los núcleos galácticos activos son lugares violentos y misteriosos, en general se presentan oscurecidos por el polvo circundante lo que dificulta su observación directa. El rango espectral del infrarrojo cercano se presenta entonces como una herramienta clave a la hora de caracterizar morfológica y cinemáticamente estas regiones. En esta tesis se presenta un estudio espectroscópico y de imágenes con resoluciones por debajo del segundo de arco de 20 galaxias. Los dat
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26

Coudé, Simon. "Étude sous-millimétrique de l’interaction entre le magnétisme et la turbulence dans les milieux interstellaires." Thèse, 2017. http://hdl.handle.net/1866/20601.

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