Dissertations / Theses on the topic 'Nuclei-quasars'

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 picture of galaxy formation. In this thesis, independent methods are developed to constrain the accretion disk and radio jet angles to the line of sight. H IX emission from a sub-sample of high-redshift quasars is measured from near-infrared spectroscopy and modelled as sums of different components, including the characteristic double-peaked profile which results from a thin, rotating accretion disk. Comparing the models using Bayesian evidence, almost all quasars were found to have infrared spectra consistent with the presence of a disk. The jet inclination angles of the same set of quasars were constrained by fitting a model, including the effect of Doppler boosting and the receding torus model for dust obscuration, to the radio \ spectral energy distribution. The fitted disk and jet angles correlate strongly, and are consistent with a model in which the radio jets are launched orthogonally to the plane of the accretion disk, as expected if the jet is powered by energy drawn from the spin of the black hole. Both disk and jet angles correlate with the observed linear source size, which is a projection effect; when deprojected using the fitted angles, the distribution of source sizes agrees with a scenario in which the sources expand into the surrounding medium at a constant rate up to ~ 1 Mpc and then shut off, probably as the nuclei become quiescent. The accretion disk angle was found to correlate weakly with the low-frequency radio luminosity, which provides direct, albeit tenuous, evidence for the receding torus model.

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 construction de systèmes de référenceultra-précis et très stables.Des instabilités en position de quelques centaines de microsecondes d’arc, généralementimputées aux variations de la structure des jets, sont toutefois souvent observées sur des échellesde temps de quelques mois à quelques années. Le travail présenté ici étudie le lien entre les deuxphénomènes de façon statistique. Sur la base d’observations VLBI régulières conduites entre1994 et 2003, nous comparons l’évolution de la position astrométrique et de la structure des jetspour un échantillon de 68 AGN sur une période de 10 ans. Les résultats de l’étude indiquent quela corrélation entre les deux phénomènes existe mais n’est pas aussi forte qu’attendue. Le travailest complété par une simulation des effets causés sur la trajectoire des jets par la précessiondu disque d’accrétion ainsi que par la présence d’un système binaire de trous noirs. Appliquéeau cas de la source 1308+326, l’étude montre que l’amplitude de ces effets est compatible avecles oscillations de la trajectoire observées en VLBI<br>Active Galactic Nuclei (AGN) are located in the center of extremely distant and bright galaxies. Their luminosity comes from the interaction between a super-massive central blackhole and an accretion disk, producing a relativistic collimated jet of matter. Thanks to the extremely high resolution achieved by Very Long Base line Interferometry (VLBI), the jet structure may be studied in detail, while the astrometric position of the AGN is determined with ahigh accuracy. Because of their location at cosmological distances, no proper motions are detected for those objects, making them ideal fiducial points for building highly-precise celestial reference frames.Instabilities up to a few hundreds of micro arc seconds are yet often observed in astrometricpositions on time scales from months to years. This is generally thought to be caused by theevolution of source structure. The study presented here investigates the correlation between the two phenomena on a statistical basis. Based on regular VLBI observations conducted between1994 and 2003, astrometric position variations and source structure evolution are compared fora sample of 68 AGN over a period of 10 years. The results indicate that a correlation between the two phenomena does exist but it is not as strong as expected. Additionally, a simulation of the effects caused by the precession of the accretion disc and the potential presence of abinary black hole in the center of the AGN is presented. Applied to the source 1308+326, the simulation shows that the magnitude of the effects is consistent with the oscillations of the jet trajectory observed on VLBI scale

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.

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 of multi-wavelength population synthesis modeling is used to study the average properties of AGN and their host galaxies with a focus on host galaxy star formation and the role of black hole growth in galaxy evolution. Knowledge of the AGN population from deep X-ray surveys is combined with theoretical AGN spectral energy distributions to predict various observables of the AGN population in wavelength regions from the far infrared to very hard X-rays. Comparison of the model predictions to observations constrains the model input parameters and allows for the determination of average properties of the AGN population. Particular attention is paid to a special class of AGN known as Compton thick AGN. These AGN are deeply embedded in gas and dust such that the column density obscuring the line of sight to the central engine of the AGN exceeds 1/σT ~ 10²⁴ cm⁻², where σT is the Thomson cross-section of the electron---a column density comparable to that of the human chest. Theoretical and simulational evidence suggest that these Compton thick AGN may be recently triggered, rapidly accreting AGN, making them of special interest to researchers. I found that Compton thick AGN are likely to contribute ~20% of the peak of the cosmic X-ray background (XRB) at ~30 keV and demonstrated that a significant portion of Compton thick AGN may be accreting very rapidly. Moreover, Compton thick AGN do not appear to follow the orientation based unified model of AGN. According to the unified model, AGN exhibit a range of obscuration levels due to a dusty 'torus' which, depending on the orientation of the torus to the observer's line of sight, may obscure the central engine of the AGN. Upon further investigation into the stellar populations of AGN host galaxies, it appears that the unified model holds in general at z < 1, but not at z > 1. I found that this is likely due to the dominant triggering mechanism of AGN switching from major mergers at z > 1.5 to secular processes by z ~ 1.

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 populations of X-ray absorbed active galaxy nuclei (AGN) in order to explain the cosmic X-ray background peak at ~30 keV. Current X-ray missions such as XMM-Newton and Chandra offer the possibility of studying these additional populations. This Ph.D. thesis studies the populations that dominate the X-ray sky. For this purpose the 120 ksec XMM-Newton Marano field survey, named for an earlier optical quasar survey in the southern hemisphere, is analysed. Based on the optical follow-up observations the X-ray sources are spectroscopically classified. Optical and X-ray properties of the different X-ray source populations are studied and differences are derived. The amount of absorption in the X-ray spectra of type II AGN, which are considered as a main contributor to the X-ray background at ~30 keV, is determined. In order to extend the sample size of the rare type II AGN, this study also includes objects from another survey, the XMM-Newton Serendipitous Medium Sample. In addition, the dependence of the absorption in type II AGN with redshift and X-ray luminosity is analysed. We detected 328 X-ray sources in the Marano field. 140 sources were spectroscopically classified. We found 89 type I AGN, 36 type II AGN, 6 galaxies, and 9 stars. AGN, galaxies, and stars are clearly distinguishable by their optical and X-ray properties. Type I and II AGN do not separate clearly. They have a significant overlap in all studied properties. In a few cases the X-ray properties are in contradiction to the observed optical properties for type I and type II AGN. For example we find type II AGN that show evidence for optical absorption but are not absorbed in X-rays. Based on the additional use of near infra-red imaging (K-band), we were able to identify several of the rare type II AGN. The X-ray spectra of type II AGN from the XMM-Newton Marano field survey and the XMM-Newton Serendipitous Medium Sample were analysed. Since most of the sources have only ~40 X-ray counts in the XMM-Newton PN-detector, I carefully studied the fit results of simulated X-ray spectra as a function of fit statistic and binning method. The objects revealed only moderate absorption. In particular, I do not find any Compton-thick sources (absorbed by column densities of NH > 1.5 x 10^24 cm^−2). This gives evidence that type II AGN are not the main contributor of the X-ray background around 30 keV. Although bias effects may occur, type II AGN show no noticeable trend of the amount of absorption with redshift or X-ray luminosity.<br>Giacconi et al. (1962) entdeckten mit Hilfe von Raketenexperimenten auf der Suche nach Röntgenstrahlung vom Mond eine scheinbar diffuse extragalaktische Röntgenhintergrundstrahlung. Spätere Satellitenmissionen detektierten ein Maximum dieser Strahlung bei ~30 keV. Abbildenden Röntgensatelliten wie ROSAT (1990-1999) gelang es, bis zu 80% des diffusen Hintergrundes unter 2 keV in einzelne Punktquellen aufzulösen, von denen die überwiegende Mehrheit aktive Galaxienkerne waren. Der Röntgenhintergrund ist somit wahrscheinlich als die Emission der Gesamtheit aller akkretierenden superschweren (mehrere Millionen Sonnenmassen) schwarzen Löcher in den Zentren von Galaxien in der kosmischen Geschichte zu verstehen. Zur Erklärung des Maximums der spektralen Energieverteilung der Röntgenhintergrundstrahlung bei ~30 keV benötigen theoretische Modelle jedoch zusätzliche Populationen von röntgenabsorbierenden aktiven Galaxienkernen (AGN). Derzeitige Röntgenmissionen wie XMM-Newton und Chandra ermöglichen die Untersuchung dieser Quellklassen. Die vorliegende Arbeit untersucht die Quellpopulationen, die den Röntgenhimmel dominieren. Dazu wird die 120 ksec XMM-Newton Beobachtung im Marano Feld, Ziel einer früheren optischen AGN-Durchmusterung am Südhimmel, ausgewertet. Die optischen und Röntgeneigenschaften der unterschiedlichen Quellpopulationen werden untersucht und Unterschiede erarbeitet. Für die röntgenabsorbierende Objektklasse der Typ II AGN, die man als möglichen Erzeuger der Röntgenstrahlung um 30 keV betrachtet, wird aus den Röntgenspektren das Ausmaß der Absorption ermittelt. Um die Anzahl dieser selten gefundenen Objekte zu erhöhen, werden in dieser Arbeit zusätzliche Objekte aus der Röntgendurchmusterung des “XMM-Newton Serendipitous Medium Sample” einbezogen. Die Abhängigkeit der Absorption von der Rotverschiebung und der Röntgenleuchtkraft wird untersucht. Von 328 Röntgenquellen im Marano Feld konnten 140 spektroskopisch klassifiziert werden. Es wurden 89 Typ I AGN, 36 Typ II AGN, 6 Galaxien und 9 Sterne gefunden. Nur basierend auf den optischen und Röntgeneigenschaften können AGN, Galaxien und Sterne unterschieden werden. Typ I und II AGN lassen sich nicht klar trennen und zeigen große Gemeinsamkeiten in den untersuchten Eigenschaften. Mit Hilfe von zusätzlichen Aufnahmen im nahen Infraroten (K-Band) konnten erfolgreich mehrere seltene Typ II AGN identifiziert werden. Die Röntgenspektren von Typ II AGN aus dem XMM-Newton Marano Feld und dem “XMM-Newton Serendipitous Medium Sample” wurden ausgewertet. Die Objekte weisen nur eine mäßige Absorption auf und scheinen somit nicht einen Hauptbestandteil des Röntgenstrahlungshintergrundes um 30 keV zu erzeugen. Obwohl Selektionseffekte nicht vollständig verstanden sind, zeigen Typ II AGN keine erkennbare Abhängigkeit der Absorption von der Rotverschiebung oder der Röntgenleuchtkraft.

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 luminosities L-X(2-10 keV) > 10(44) erg s(-1), independent of redshift. For less luminous sources, the fraction of obscured Compton-thin AGNs increases from 0.45 +/- 0.10 at z = 0.25 to 0.75 +/- 0.05 at z = 1.25. Studies that select AGNs in the infrared via template fits to the observed spectral energy distribution of extragalactic sources estimate space densities at high accretion luminosities consistent with the XMM-XXL constraints. There is no evidence for a large population of AGNs (e.g. heavily obscured) identified in the infrared and missed at X-ray wavelengths. We further explore the mid-infrared colours of XMM-XXL AGNs as a function of accretion luminosity, column density and redshift. The fraction of XMM-XXL sources that lie within the mid-infrared colour wedges defined in the literature to select AGNs is primarily a function of redshift. This fraction increases from about 20-30 per cent at z = 0.25 to about 50-70 per cent at z = 1.5.

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 will steepen the high frequency region of the spectrum unless inverse Compton scattering is effective. In many cases accretion flow in the central part of the cluster will be optically thick to electron scattering resulting in a spectrum featuring optically thick radiative component in addition to power -law regimes. The fitting of these spectra to QSO and AGN observations is discussed, and application to 3C 273 is worked out as an example.

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 quando l’Universo aveva meno di 1 miliardo di anni. Come si sono formati e che tipo di meccanismo ha agito sulla loro crescita in così poco tempo? Per aumentare la sua massa, l’accrescimento di gas deve aver proceduto quasi continuamente vicino al limite di Eddington. Rompendo la condizione di equilibrio tra la forza di gravità e la pressione di radiazione, ci si potrebbe aspettare una variabilità più pronunciata nell’accrescimento dei quasar con il redshift più alto, quindi nella loro luminosità. La maggior parte dei quasar attualmente noti a z≈6 sono stati scoperti grazie a survey profonde e su larga scala. Ad oggi, a distanza di 20 anni dalle prime rilevazioni, siamo in grado di ricercare qualsiasi indicazione di variabilità anche per quasar ad alto redshift. In questo lavoro di tesi, utilizzando il Telescopio Cassini da 152 cm di Loiano, ho osservato un piccolo campione di quasar luminosi con magnitudine ≈18−20 nella banda z a redshift z>5.5. Dopo la riduzione e l’analisi dei dati, ho ottenuto la magnitudine delle sorgenti osservate per confrontarle con i risultati di SDSS, Pan-STARRS e DECaLS. Come risultato, ho riscontrato una diversità nel comportamento di queste sorgenti: alcuni oggetti non mostrano evidenza di variabilità, mentre per altri sembra esserci un andamento consistente nell’aumento o diminuzione del flusso osservato rispetto alle osservazioni con le altre survey

``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) quasar surveys in both Sloan Digital Sky Survey and Very Large Telescopes (VLT), we determined various physics properties of quasar absorption outflows, e.g., the electron number density (ne), the distance of outflows to the central quasar ($R$), and the kinetic energy carried by the outflow ($dot{E}_{k}$). We demonstrated that half of the typical BAL outflows are situated at $R$ $>$ 100 pc, i.e., having the potential to affect the host galaxies. (2). Our group carried out a Hubble Space Telescope program (PI: Arav) for studying the outflows in the Extreme-UV, collaborating with Dr. Gerard Kriss from Space Telescope Science Institute (STScI). We developed a novel method to fit the multitude of quasar absorption troughs efficiently and accurately. We have identified the most energetic quasar-driven outflows on record and discovered the largest acceleration and velocity-shift for a quasar absorption outflow. (3). By using the VLT data, Xu led the project to study the relationships between BAL outflows and emission line outflows. We found possible connections between these two types of quasar outflows, e.g., the luminosity of the [oiii] ly 5007 emission profile decreases with increasing ne derived from the BAL outflow in the same quasar. These findings are consistent with BAL and emission outflows being different manifestations of the same wind, and the observed relationships are likely a reflection of the outflow density distribution.<br>Doctor of Philosophy<br>Super massive black holes (SMBHs) are believed to exist in the center of almost all massive galaxies, where the brightest accreting ones are named ``quasars''. ``Quasar-mode feedback'' occurs when momentum and energy from the environment of accreting SMBHs 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. Such quasar outflows are invoked to explain a variety of observations, e.g., the chemical enrichment of the intergalactic medium (IGM), the shape of the observed quasar luminosity function, and the self-regulation of the growth of the SMBHs. In this dissertation, I focus on studying the emission and absorption outflows observed in quasars spectra, collected with the largest telescopes and most powerful instruments in the world. (1). By conducting large broad absorption line (BAL) quasar surveys in both Sloan Digital Sky Survey and Very Large Telescopes (VLT), we determined various physics properties of quasar absorption outflows, e.g., the electron number density (ne), the distance of outflows to the central quasar ($R$), and the kinetic energy carried by the outflow ($dot{E}_{k}$). We demonstrated that half of the typical BAL outflows are situated at $R$ $>$ 100 pc, i.e., having the potential to affect the host galaxies. (2). Our group carried out a Hubble Space Telescope program (PI: Arav) for studying the outflows in the Extreme-UV, collaborating with Dr. Gerard Kriss from Space Telescope Science Institute (STScI). We developed a novel method to fit the multitude of quasar absorption troughs efficiently and accurately. We have identified the most energetic quasar-driven outflows on record and discovered the largest acceleration and velocity-shift for a quasar absorption outflow. (3). By using the VLT data, Xu led the project to study the relationships between BAL outflows and emission line outflows. We found possible connections between these two types of quasar outflows, e.g., the luminosity of the [oiii] ly 5007 emission profile decreases with increasing ne derived from the BAL outflow in the same quasar. These findings are consistent with BAL and emission outflows being different manifestations of the same wind, and the observed relationships are likely a reflection of the outflow density distribution.

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 una delle caratteristiche di tutti gli AGN. Il breve tempo scala (103-105 s) delle variazioni di flusso X fornisce evidenza che l'emissione provenga da una regione compatta intorno al buco nero centrale supermassivo. Gli studi teorici (Shakura &amp; Sunyaev 1973) riescono a spiegare l'emissione ottica ed ultravioletta come proveniente da un disco di accrescimento stabile e otticamente spesso, ma non sono in grado di fornire una spiegazione sull'origine dell'emissione mella banda X. È inoltre noto che le luminosità X e ultavioletta (UV) dei quasar sono tra loro correlate e studi recenti hanno accertato questa dipendenza su cinque ordine di grandezza (e.g. Strateva et al. 2005; Gibson et al. 2008) . Queste analisi cercano di comprendere la struttura e la fisica delle regioni nucleari dei quasar, ponendo dei vincoli sui modelli di connessione fisica tra le emissioni nella banda X ed in quella UV. Dal momento che si ritiene che i fotoni UV provengano dal disco di accrescimento, mentre i raggi X sono supposti essere originati in una corona che circonda il disco, lo studio del rapporto UV/X dà informazioni sull'equilibrio tra i dischi di accrescimento e le loro corone. In questo contesto, la mia tesi presenta alcuni risultati sulla relazione tra luminosità X e UV da osservazioni simultanee nelle bande X ed UV per un campione di quasar con dati estratti dall'archivio del satellite XMM-Newton (see Vagnetti et al. 2010a, for details). Alcune indicazioni sulla natura della variabilità possono essere ottenuti dall'analisi dello spettro di potenza, o della funzione di struttura, di curve di luce in singola banda. A parte lo studio delle curve di luce individuali, le proprietà d'insieme di campioni statistici di quasar (QSO) possono fornire ulteriori vincoli sull'origine della variabilità. Nelle bande ottiche l'analisi d'insieme di grandi campioni ottici (25000 sorgenti) è stata resa possibile dalla Sloan Digital Sky Survey (SDSS) ed ha permesso di caratterizzare la dipendenza della variabilità ottica con la luminosità, il redshift, la lunghezza d'onda e il ritardo temporale (Vanden Berk et al. 2004; de Vries et al. 2005). Un'analisi analoga non è stata ancora effettuata nella banda X ed ora diventa possibile grazie al campo di vista relativamente grande tipico della strumentazione X, quale quella a bordo dei satelliti XMM-Newton e Swift, che permette di recuperare dati dai campi di osservazioni individuali. Attualmente due database sono disponibili per questo tipo di studi, ovvero il Secondo Catalogo Serendipito di XMM (Watson et al. 2009) e il Catalogo Serendipito dei Campi Profondi centrati sui GRB osservati da Swift (Puccetti et al. 2010). Il primo è limitato, dai vincoli dell'orbita del satellite, a dati per variazioni su lunghi tempi scala (diversi mesi) e soffre di un campionamento temporale piuttosto rado. Al contrario il catalogo del satellite Swift fornisce un campionamento su tempi scala intermedi (da ore ad pochi mesi) per un numero di sorgenti sufficiente a calcolare una Funzione di Struttura d'insieme. Costruire una Funzione di Struttura d'insieme per gli AGN richiede di accertare la natura delle sorgenti serendipite X, in modo da escludere eventuali stelle e galassie normali che emettono in banda X, e conoscere il redshift delle sorgenti in modo da poter raggruppare tutte le variazioni di flusso individuali da in intervalli di ritardo temporale nel sistema di riferimento di quiete. Questa tesi presenta le prime Funzioni di Struttura della variabilità X per due campioni di quasar con spettri ottici dalla SDSS-DR7: ho utilizzato dati d'archivio dai cataloghi serendipiti dei satelliti Swift e XMM per ottenere una curva di crescita della variabilità X con l'intervallo temporale. L'esponente di scala della parte della Funzione di Struttura descrivibile a legge di potenza contiene importanti informazioni sul meccanismo di variabilità e potrebbe in principio essere usato per porre vincoli sui modelli di emisioni o sulle proprietà fisiche degli AGN. In questa tesi, segnalo che ho trovato Funzioni di Struttura regolari, ovvero esse non mostrano alcuna piega da poter mettere in relazione con la massa del buco nero MBH o la luminosità bolometrica Lbol o entrambe le grandezze. Infine, questa tesi presenta i risultati preliminari della campagnia di indetificazione ottica di acune sorgenti serendipite del satellite Swift condotta al TNG e sulle sorgenti radio serendipite con dati dalla SDSS-DR7 (Abazajian et al. 2009) scoperti nei campi profondi del satellite Swift.<br>Active Galactic Nuclei (AGNs) show flux variations over the entire electromagnetic spectrum. Indeed, variability was one of the first recognized properties of quasars. Although variability plays a key role in constraining the size of the central engine of AGNs, its physical origin remains substantially unknown. Many mechanisms have been proposed to explain optical observations, such as supernova explosions, star capture, gravitational microlensing or disc instabilities. Rapid X-ray variability is indeed a hallmark of AGNs. X-ray short time scale (103-105 s) variability provides evidence that the emission comes from a compact region around the central supermassive black hole. Whereas theoretical studies (Shakura &amp; Sunyaev 1973) provide an explanation of the optical-UV radiation from a steady, optically thick, accretion disc, they cannot explain the X-ray emission. Moreover, it is known that UV and X-ray luminosities of quasars are correlated and recent studies quantified this relation across 5 orders of magnitude (e.g. Strateva et al. 2005; Gibson et al. 2008) . Such studies inform ongoing efforts to understand the structure and the physics of quasars nuclear regions, providing constraints on models of physical associations between UV and X-ray emissions. Because UV photons are generally thought to be radiated from the accretion disc whereas X-rays are produced in the disc corona, the UV/X-ray luminosity relation is an indication of the balance between accretion discs and their coronae. In this context, I present in this thesis some results on the X-ray/UV relation from simultaneous observations in UV and X-ray bands of a sample of quasars with data from XMM-Newton archive (see Vagnetti et al. 2010a, for details). Some indication on the nature of variability can be obtained from the analysis of the power spectrum, or the structure function, of single-band lightcurves. Besides the study of individual lightcurves, ensemble properties of statistical quasar (QSO) samples can provide further constrains on the origin of variability. In the optical bands the ensemble analysis on large optical samples (25,000 objects) was made possible by the Sloan Digital Sky Survey (SDSS), and provided a characterization of the dependence of optical variability on luminosity, redshift, wavelength and time delay (Vanden Berk et al. 2004; de Vries et al. 2005). A similar analysis has not yet been performed in the X-ray, and now becomes possible thanks to the relatively wide field-of-view of typical X-ray instrumentation, such as those on-board XMM-Newton and Swift satellites, to retrieve field data from individual pointed observations. Two available databases are suitable for this analysis, i.e. the Second XMM-Newton serendipitous source catalogue (Watson et al. 2009), and the Swift Serendipitous Survey in deep XRT GRB fields (Puccetti et al. 2010). The former is limited, by orbital constraints, to long timescale (several months) variations and suffers for rather sparse sampling. On the contrary the Swift catalog provides a sampling at intermediate timescales (hours to a few months) for a number of objects sufficient to calculate an ensemble SF. To build an ensemble SF of the AGNs, it is necessary to ascertain the AGN nature of the X-ray serendipitous sources, excluding possible X-ray emitting stars or galaxies, and to know the redshifts of the sources in order to group all the individual flux variations of different objects in bins of rest-frame time lag. This thesis presents the first ensemble Structure Functions (SFs) of the X-ray variability of two samples of quasars with SDSS-DR7 optical spectra: I used archival data from the Swift and XMM serendipitous source catalogs to obtain a curve of growth of X-ray variability with time lag. The index of the power law portion of the SF contains important information on the variability mechanism and could in principle be used to put constraints on emission models or AGNs physical properties. Here, I report that I found smooth SFs, i.e. they do not show any bend to be related with the black hole mass MBH or the bolometric luminosity Lbol or both. Moreover, I present here results regarding the TNG optical identification campaign of some Swift serendipitous sources and the preliminary results on the serendipitous radio sources with SDSS-DR7 data (Abazajian et al. 2009) detected in Swift GRB deep fields.

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 durch Beobachtungen mit dem Fermi Gamma-ray Space Teleskop und durch Multiwellenlängendaten unterstützt. Es werden zwei Aktive Galaxien mit Jet untersucht: PKS 1510-089 und NGC 1275. Die MAGIC Teleskope, welche PKS 1510-089 seit 2012 immer wieder beobachten, detektieren eine signifikante Emission über dutzende von Observationsstunden, was auf schwache aber kontinuierliche Gammastrahlung aus dieser Quelle hinweist. NGC 1275 zeigte in der Periode von September 2016 bis Februar 2017 einen großen Ausbruch im Gammerstrahlenbereich: MAGIC zeichnete eine Variabilität in der Größenordnung von wenigen Stunden und die erstmalige Emission von TeV Photonen. Aus beiden untersuchten Quellen ist ersichtlich, dass die Kombination von Daten aus verschiedenen Instrumenten die physische Diskussion entscheidend beeinflusst. Der Übergang zu zugänglichen und interoperablen Daten wird zu einem zwingenden Thema für Gammastrahlenastronomen, und diese Arbeit stellt das technische Bestreben dar, standardisierte hochrangige Daten für Gammastrahleninstrumente zu erzeugen. Ein Beispiel für eine zukünftige Analyse, die einheitliche High-Level-Daten von einem Gammastrahlensatelliten und vier Cherenkov-Teleskopen kombiniert, wird vorgestellt. Der neue Ansatz, der vorgeschlagen wird, führt die Datenanalyse durch und verbreitet die Ergebnisse, wobei nur Open-Source-Ressourcen verwendet werden.<br>Powered by the accretion of matter to a supermassive black hole, active galactic nuclei constitute the most powerful and persistent sources of radiation in the universe, with emission extending in the gamma-ray domain. The aim of this work is to characterise the mechanisms and sites beyond this highly-energetic radiation employing observations of two galaxies at hundreds of GeV, conducted with the MAGIC imaging Cherenkov telescopes. The physical interpretation is supported with observations by the Fermi Gamma-ray Space Telescope and with multi-wavelength data. Two peculiar jetted galaxies are studied: PKS 1510-089 and NGC 1275. The first source, monitored by MAGIC since 2012, presents a significant emission over tens of observation hours, in what appears to be a low but persistent gamma-ray state. The second source has instead shown, in the period between September 2016 and February 2017, a major outburst in its gamma-ray activity with variability of the order of few hours and emission of TeV photons. The broad band emission of jetted galaxies is commonly modelled with the radiative processes of a population of electrons accelerated in the jet. While PKS 1510-089 conforms to this scenario, modelling the gamma-ray outburst of NGC 1275 requires placing the acceleration and radiation of electrons close to the event horizon of the black hole. From both the sources studied it is evident that the combination of data from different instruments critically drives the physical discussuion. Moving towards accessible and interoperable data becomes a compelling issue for gamma-ray astronomers and this thesis presents the technical endeavour to produce standardised high-level data for gamma-ray instruments. An example of a future analysis combining uniformed high-level data from a gamma-ray satellite and four Cherenkov telescopes is presented. The novel approach proposed performs the data analysis and disseminates the results making use only of open-source assets.

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 ces objets.<br /><br />Cette thèse de doctorat est dédiée à l'étude des propriétés des AGN de type 1 de faible luminosité. Dans ce but nous utilisons un échantillon spectroscopique de 130 AGN à raies<br />d'émission larges, extrait d'un grand relevé de galaxie: le VIRMOS VLT Deep Survey (VVDS).<br />Cet échantillon présente un intérêt unique, de part la simplicité des critères de pré-sélection de ces objets (une simple limite en magnitude) ainsi que par la profondeur en magnitude atteinte: il fournit d'une part un aperçu des propriétés des AGN de type 1 à des magnitudes encore peu explorées spectroscopiquement (les AGN étudiés ici sont jusqu'à cent fois plus faibles que ceux du SDSS) et il permet d'autre part de quantifier les biais qui seraient introduits par des critères classiques de sélection.<br /><br />Nous mesurons une densité sur le ciel d'environ 470 AGN par degré carré à notre magnitude limite (Iab=24). Une fraction importante des AGN que nous observons ne serait pas sélectionée par les techniques de sélections morphologiques et d'excès d'UV classiquement appliquées. Nous attribuons cet effet à la contamination de nos AGN par leur galaxie hôte, vue leur faible luminosité. La fonction de luminosité des AGN montre qu'il y a relativement plus d'AGN de faible luminosité à bas redshift qu'á plus grand redshift. Cette observation corrobore le scénario de croissance anti-hierarchique de trous-noirs galactiques suggéré par les echantillons d'AGN sélectionnés en rayons-X.<br />Finalement nous nous sommes intéressés à la nature des trous noirs qui sont à l'origine de nos AGN. S'agit-il de petits trous noirs galactiques ou bien, au contraire, de trous noirs de grandes masses accrétant faiblement ?<br />Nos résultats, encore préliminaires, suggèrent que nos AGN correspondent en moyenne à des trous noirs galactique de masses intermediaires (~100 millions de masses solaires) accrétant à des taux d'Eddington modeste (~< 10%).

<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 central components of six double-lobed quasars have been mapped at high resolution and high sensitivity with VLBI. Each object exhibits a double or extended structure on the the ~parsec scale. This structure can be interpreted as a "core-jet," the same morphology found in the dominant cores of powerful flat-spectrum sources, thus indicating a relation between the two classes of compact radio source. The presumed VLBI jets are all fairly well aligned with &gt;~kiloparsec-scale, one-sided jets. The fact that the VLBI and large-scale jets always lie on the same side of the compact core suggests the same cause for the asymmetric structure on both scales.</p> <p>The central components of 3C245 and 3C263 have been mapped at three epochs. We find superluminal expansion in 3C263 with an apparent velocity of ~1.5c, and argue that there is evidence that 3C245 will also be found to be superluminal. These results are consistent with the simple beaming theory. It is thus clear that we will be able to measure component motion in many of these objects, which will permit us to distinguish among alternative theories of parsec-scale structure and motion.</p> <p>The future study of these compact central components will benefit greatly from the increased resolution afforded by both higher frequency, ground-based VLBI and VLBI using a radio telescope in Earth orbit.</p>

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

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.<br>text

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 understand how galaxies formed and evolved in the Universe. The small size and the distance of these sources imply that the emitting regions are spa- tially unresolved, making the spectroscopic analysis the only tool available for their study. AGN are characterised by strong emission features, coming from specific regions: the Broad Line Region and the Narrow Line Region. These lines show profiles far broader than the normal galactic emissions and are hence necessarily emitted by gas under the influence of a very strong gravitational field. Their presence in AGN spectra is therefore a confirmation that the central engine of AGN consists of a SMBH; furthermore, it enables us to give an estimation of the mass of the central body and, through the analysis of their shape, makes us able to study the geometry and the kinematics of the emitting regions. This thesis fits in this context. We are interested in the study of emissions coming from the structures depicted in the AGN Unified Model and, particularly, in the emission lines coming from the BLR, the closest to the SMBH and therefore the one providing information on its mass.

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 complete the census of the extreme SMBH population in the universe. We found that the 70% of quasars lacks [OIII] emission but shows strong winds traced by 3000-8000 km/s blueshifts of the high-ionization (CIV) with respect to low-ionization (HBeta) broad emission lines, revealing strong radiatively driven winds that dominate the BLR kinematics. We investigated about the possible origins of this intriguing dichotomy which involves fundamental parameters such as bolometric luminosity, SMBH mass, Eddington ratio and shape of the UV-X-ray spectrum.

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 datos utilizados fueron tomados en los telescopios Gemini con los instrumentos Flamingos-2 y GNIRS. Los estudios abordados involucran, en síntesis, la búsqueda de núcleos descentrados (los cuales están relacionados con la alimentación de los mismos), caracterización de las estructuras nucleares de polvo caliente y estudio de la cinemática del gas nuclear en sus distintas fases.<br>Active galactic nuclei are violent and mysterious places, in general they appear as obscured by circumnuclear dust which makes their direct observation difficult. The Near Infrared spectral range is then a key tool when characterizing these regions both morphologically and cinematically. In this thesis an sub-arcsecond spectroscopic and imaging study of 20 galaxies is presented. The data was taken with the instruments Flamingos-2 and GNIRS at Gemini telescopes. The studies addressed include the search for off-centered nuclei (which is related to their feeding mechanism), the characterization of the nuclear hot dust structures and the study of the cinematic of the nuclear gas in its different phases.<br>Fil: Gaspar, Gaia. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación; Argentina.