Clusters of galaxies provide a unique opportunity to simultaneously study cosmology through low scatter scaling relations and the complex baryonic physics that occurs in cluster cores. As such it is of key importance to quantify the effects of the various physical processes that drive cluster evolution. In this thesis a sample of 30 clusters from the Millennium Gas Simulation, of masses 10^14/h Solar Masses < M200 < 10^15/h Solar Masses, were selected and run at a higher resolution using the re-simulation technique, using a modified version of Gadget-2, an N-body SPH code. Each cluster was run multiple times with increasing levels of sub-grid physics in order to separate the different effects that govern cluster evolution. The models implemented starting with non-radiative (NR), simulations then added cooling and star formation (CSF), supernova feedback (SFB) and AGN feedback model (AGN) respectively. In order to best match observations a study of supernova and AGN feedback parameters was conducted. The sample of clusters were also used to quantify the magnitude of biases created when observing clusters, in an attempt to classify the accuracy of these measurements of clusters. Additionally, the effects of the biases were also included in the estimation of the cluster mass using hydrostatic equilibrium. The best match to the observed gas, star and baryon fractions, scaling relations and gas profiles was found when powerful supernova feedback was included, which heats gas particles to 10^7K, and an AGN model whose heating temperature scales with the final virial temperature of the cluster, so that particles in a 10^14/h Solar masses and 10^15/h Solar Masses cluster are heated to 10^8K and 10^8.5 K respectively. Outside the core, this model successfully matches all the observed profiles and scaling relations excluding the spectrascopic-like temperature. The core region is simulated with come success, with pressures matching those observed but gas that is too cool and dense, resulting in an inability to reproduce the non cool core entropy profiles. Cold dense gas is more heavily weighted in the spectrascopic-like temperature, allowing significant contributions from gas in substructures and cold dense clumps of gas that are un-ascociated with any substructures and seems to be an artificial construct of SPH. When this gas is removed using the method outlines in \cite{Roncarelli2006}, temperatures outside the core match observations, but the core region is still too dense and cool. Clearly this core region requires more complex physics, possibly through implementation of an improved SPH code or more complex sub-grid physics such as that associated with the AGN feedback. The bias profiles also exhibit a similar sensitivity to the cool dense gas clumps, having a profound effect on the observed profiles and creating significant scatter in the mass estimated using hydrostatic equilibrium. Removing this cold dense gas using the Roncarelli method results in reduced biases and hydrostatic mass estimates closer to the true values. The resulting scaling relations and profiles including the effects of biases differ from those without the biases, but not significantly. It is clear that biases can affect the observed profiles and scaling relations, but this effect is minimised by excluding the coldest densest gas. As the choice of how much gas is removed is somewhat arbitrary, it is clear that further work in this field would require better SPH implementations that do not produce the erroneous dense gas clumps and the generation of mock observations using the simulated data.

No description available.

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.

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. / 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.

I study mid-infrared and star formation properties of AGN samples using infrared observations, and star-forming galaxies using radio observations in order to investigate the link between star formation, AGN activity and radio luminosity. I present the results of these investigations in this thesis. I carried out an analysis of four complete samples of radio-loud AGN (3CRR, 2Jy, 6CE and 7CE) using near- and mid-IR data taken by the Wide-Field Infrared Survey Explorer (WISE). The combined sample consists of quasars and radio galaxies, and covers a redshift range 0:003 < z < 3:395. The dichotomy in the mid-IR properties of low- and high-excitation radio galaxies (LERGs - HERGs) is analysed using large complete samples. The results show that a division in the accretion modes of powerful LERGs and HERGs clearly stands out in the mid-IR radio plane. Evaluation of the positions of the sample objects in WISE colour-colour diagrams shows that widely used WISE colour cuts are not completely reliable in selecting AGN. I examined the link between AGN activity and star formation by constructing matched samples of local (0 < z < 0:6) radio-loud and radio-quiet AGN in the Herschel-ATLAS fields. AGN accretion and jet powers in these active galaxies are traced by [OIII] emission-line and radio luminosity, respectively. Star formation properties were derived using Herschel 250-_m and stellar mass measurements are taken from the SDSS-MPA-JHU catalogue. The stacking analyses show that star formation rates (SFRs) and specific star formation rate (SSFRs) of both radio-loud and radio-quiet AGN increase with increasing AGN power but that radio-loud AGN tend to have lower SFR. Additionally, radio-quiet AGN are found to have approximately an order of magnitude higher SSFRs than radio-loud AGN for a given level of AGN power. The difference between the star formation properties of radio-loud and -quiet AGN is also seen in samples matched in stellar mass. I also investigated the relationship between SFR and low-frequency radio luminosity observed in star-forming galaxies. I used a sample of star-forming galaxies in the 19 local Universe selected from the SDSS-MPA-JHU catalogue. LOFAR observations of the Herschel-ATLAS North Galactic Pole field (NGP) were carried out as part of the LOFAR surveys Key Science Project at an effective frequency of 150 MHz, which provided low-frequency radio luminosity of sample galaxies. SFRs of galaxies in the sample were derived using MAGPHYS spectral energy distribution (SED) fitting. The results of this study show that the slope of L150/SFR is less than unity and not universal for all star-forming galaxies (SFGs) in the local Universe (0 < z < 0:3). The slope of the L150/SFR relation is also found to be steeper than the L1:4/SFR relation, probably due to the contribution from thermal radio emission at 1.4 GHz. If the L150=SFR relation for strongly star-forming objects is explained naively by electron calorimetry, I conclude that low luminosity sources are not ideal calorimeters and differ from the main locus of SFGs at low redshifts. The different gradients we obtain for the far- IR/radio correlation using samples selected at different frequencies reveal the selection effects on relations derived in this thesis.

No description available.

We implement a model for, and study the effects of, AGN feedback in cosmological hydrodynamical simulations. In our model, black holes form high-density, primordial gas, to imitate the likely channels of black hole formation in the early Universe. We find that a black hole seed mass of 10²⁻³h⁻¹M⊙ is required to produce simulations that match the cosmic star formation rate density, and present-day black hole mass - velocity dispersion and galaxy size - velocity dispersion relations. We therefore suggest that Population III stars can be the progenitors of the super-massive black holes seen today. Using our fiducial model, we run two large simulations ((25h⁻¹ Mpc)³), one with and one without AGN feedback. With these, we follow the population of galaxies that forms across cosmic time, and find that the inclusion of AGN feedback improves the agreement of simulated and observed galaxy properties, such as the mass and luminosity functions. This agreement is best at z = 0, and fairly good out to z = 2-3. Evidence for downsizing in the evolution of galaxies is found, both in the present-day colour-magnitude and [α/Fe]-velocity dispersion relations, and by the fact that high-mass galaxies attain their present-day metallicity earlier and faster than do low-mass ones. With our hydrodynamical simulations, we can also investigate the internal structure of galaxies, and look at the effects of galaxy mergers and AGN feedback on the stellar and gas-phase metallicity gradients of galaxies. Stellar metallicity gradients are found to be sensitive to galaxy mergers, while gas-phase metallicity gradients are more affected by AGN activity. This suggests that simultaneous measurements of these two quantities can help disentangle the actions of mergers and AGN feedback on a galaxy's history. Finally, we develop a new method to identify massive AGN-driven outflows from the most massive simulated galaxy. These events cause the intra-cluster medium to be hotter and more chemically enriched compared to the simulation without AGN feedback, and therefore AGN feedback may be required in order to attain the metallicities observed in clusters.

La BLR (broad line region) d’un noyau galactique actif (AGN) transporte la matière du tore de poussière vers le disqued’accrétion autour d’un trou noir super massif. Il faut connaître sa géométrie pour comprendre la formation et la croissancedu trou noir, comme ses relations avec la luminosité du noyau. L’échographie lumineuse ou « reverberation mapping » permetd’estimer le rayon équivalent de la BLR ainsi que la masse du trou noir et donne des lois masse-luminosité et rayon-luminositédont la précision, limitée par les inconnues géométriques, reste insuffisante pour des applications cosmologiques.L’interférométrie optique avec le VLTI donne des mesures indépendantes de cette masse et de ces paramètres géométriqueset mesure un rayon angulaire équivalent, ce qui donne une mesure directe de distance. Nous avons développé un modèle 3Dde BLR et une méthode Bayésienne d’ajustement des paramètres qui nous ont permis de montrer que la combinaison del’échographie et de l’interférométrie donnera des mesures de masse et de distance à mieux que 15% près à un milliard deparsec. Nous appliquons ces outils aux toutes premières observations avec l’instrument AMBER de la BLR du quasar 3C273et nous montrons et expliquons qu’elle est bien plus grande que prédit par échographie et s’étend au delà du bord interne dutore de poussière, avec une géométrie quasi sphérique. Ces résultats sont extrapolés à la nouvelle génération d’instrument duVLTI pour montrer que cet interféromètre permettra de calibrer les méthodes échographiques pour transformer les quasarsen sondes cosmologiques majeures. / The broad line region (BLR) of Active Galactic Nuclei (AGN) contains the high velocity gas clouds transporting materialfrom the dust torus to the accretion disk around the central super massive black hole (SMBH). Unveiling BLR structure iscritical to understand the accretion mechanism driving the SMBH evolution and shaping the AGN inflows, outflows and jets.Reverberation Mapping (RM) constrains the BLR geometry, kinematic, mass and equivalent linear size with parameterdegeneracies and fudge factors depending from the source geometry. Optical Interferometry (OI) yields independentconstrains on BLR structure, mass and equivalent angular size. We developed a 3D geometrical model of BLRs to estimateboth RM and OI measures and to show that the combination of these two techniques will very substantially reduce theuncertainty of mass estimates and yield direct distance measurement from “quasar parallax”. We used this model and a MonteCarlo Markov Chain Bayesian parameter fit of simulated data to show that quasar parallax can measure distances withaccuracy better than 15%. We used it on actual data to interpret and explain our first OI observations of the BLR of thebright quasar 3C273 found to have a BLR of about 1750±35 light days (ld) much larger than predicted by RM (450±120 ld)and larger than the inner rim of the dust torus of about 800±270 ld, yielding a SMBH mass of 5±1 108 solar masses. Ourmodel and SNR computations show that the VLTI incoming instruments can observe about 60 BLRs covering more than 4decades of luminosity, enough to try a grand unification of BLRs models and a calibration of RM making QSOs majorcosmological probes.

No description available.

Quasar outflows are a major candidate for Active Galactic Nuclei (AGN) feedback, and their capacity to influence the evolution of their host galaxy depends on the mass-flow rate (M) and kinetic luminosity (E) of the outflowing material. Both quantities require measurement of the distance (R) to the outflow from the central source as well as physical conditions of the outflow, which can be determined using spectral observations of the quasar. This thesis presents spectral analyses leading to measurements of R, M and E for three different quasar outflows. Analysis of LBQS J1206+1052 revealed multiple diagnostic spectral features that could each be used to independently determine R. These diagnostics yielded measurements that were in close agreement, resulting in a robust outflow distance of 840 pc from the central source. This measurement is much larger than predicted from radiative acceleration models (~0.01-0.1 pc), suggesting that outflows appear much farther from the central source than is generally assumed. The outflow in SDSS J0831+0354 was found to carry a kinetic luminosity of 10^45.7 erg/s, which corresponds to 5.2 per cent of the Eddington luminosity of the quasar. This outflow is one of the most energetic outflows to date and satisfies the criteria required to produce AGN feedback effects. A variability study of NGC 5548 revealed an obscuring cloud of gas that shielded the outflow components, dramatically lowering their ionization state. This resulted in the appearance of absorption from the rare element Phosphorus, as well as from sparsely-populated energy levels of CIII and SiIII. These spectral features allowed for an accurate determination of R and for constraints on the ionization phase to be obtained. The latter constraints were used to develop a self-consistent model that explained the variability of all six outflow components during five observing epochs spanning 16 years. / Ph. D.