In this dissertation, I present my work on the behaviour of different features of radio-loud active galaxies to investigate how energy is transferred from their jets to the environment. To this end, I have studied the knots in the jet in Centaurus A, the radio and X-ray emission from the lobes of the FRII radio galaxies 3C 353 and Pictor A, and the gas properties of a sample of galaxy groups some of which host radio-loud AGN. Using new and archival multi-frequency radio and X-ray data for Centaurus A obtained over almost 20 years with the Very Large Array and with Chandra, I have measured the X-ray and radio spectral indices, flux density variations, polarisation variations and proper motions of the jet knots. I used these measurements to constrain the likely knot formation mechanisms and particle acceleration processes within this jet and compared my results with the variations detected in the properties of the knots in M87. I found that none of the knots are a result of impulsive particle acceleration and that those knots that are detected in both X-ray and radio are likely due to collisions between the jet and an obstacle, while the radio only knots, the majority of which are moving, are likely due to compressions of the fluid flow. Using six frequencies of new and archival radio data and new XMM-Newton observations of 3C 353, I show that inverse-Compton emission is detected in the lobes of this source. By combining this X-ray emission with the radio synchrotron emission, I have constrained the electron population and the magnetic field energy density in the lobes of this radio galaxy. I have argued that the variations in the X-ray/radio ratio in the brighter lobe requires a changing magnetic field strength. I have extended this work using a statistical analysis of the X-ray and radio emission to show that the observed small-scale variation in surface brightness cannot be reproduced by simple combinations of the electron energy distribution and the magnetic field strength. I therefore suggest that the changes in surface brightness that give rise to the filamentary structures seen in the lobes are probably due to strong spatial variations of the magnetic field strength. Finally, I present a study of galaxy groups observed with XMM-Newton in which I measure temperature and surface brightness profiles to examine whether radio-source heating makes radioloud groups hotter and more luminous than radio-quiet groups. I compare my measurements with previous luminosity-temperature relationships and conclude that there is a significant difference in the gas properties of radio-loud and radio-quiet groups.

In this thesis I study the links between Active Galactic Nuclei (AGN) and their surrounding large scale environments mainly at high redshift. I firstly use Spitzer space telescope data for one of the largest and most uniformly selected samples of radio-loud and radio-quiet AGN at high redshift. It consists of 173 AGN of both type-1 Sloan Digital Sky Survey (SDSS) Quasi- Stellar-Objects (QSOs) and type-2 radio-galaxies at the single cosmic epoch of z ∼ 1. I find significant (8 σ) over-densities of galaxies in the AGNs’ environments when compared to an offset field. Further to this I address the question of whether radio-loud AGN are found, on average, in denser environments than their radio-quiet counterparts. I show that there is a link between the environment and radio luminosity of the most powerful radioloud QSOs and RGs in the sample, and also reconcile the conflicting results in the literature by suggesting that there is only a link to the environment at the highest radio powers. I extend this work to higher redshift with data from the Spitzer extragalactic Representative Volume Survey (SERVS) and type-1 SDSS QSOs in the regions covered by SERVS. This deep data allowed me to study the environments of QSOs in the redshift range 1 < z < 4. Again I find significant (4 σ) over-densities of galaxies around the QSOs in this sample, this time making use of the 3.6-4.5 μm colour to select galaxies more likely to reside at the redshifts of interest. I show that the environments of these QSOs are comparable to those predicted for similarly large black holes in the Durham semi-analytic galaxy formation model (Galform). Finally I use data from the Herschel-Astrophysical Terahertz Large Area Survey with the recently launched Herschel space observatory to study the environments of type-1 QSOs in the far-infrared (FIR). I find a small excess of galaxies around the QSOs for which I find that the star-formation rate increases with increasing redshift. The star-formation rates are estimated by modelling the FIR spectral energy distribution of the galaxies with a modified black-body spectrum. This follows the general increase in starformation rate with redshift observed in the Universe as a whole. I also compare these findings with those made by the Submillimeter Common-User Bolometer Array (SCUBA) of higher redshift QSOs.

Thesis (Ph.D.)--University of Melbourne, School of Physics, 2008. / Typescript. Includes bibliographical references (leaves 161-176).

Although the contribution to the Isotropic Gamma-Ray Background (IGRB) from unresolved extragalactic objects has been studied for many years, its exact composition and origin are as of yet unknown. It is suspected that diffuse processes such as dark matter annihilation contribute to the total IGRB, as well as unresolved gamma-ray emission from Active Galactic Nuclei (AGN), including radio galaxies. Radio galaxies are a source class that emit strongly at radio wavelengths, some of which have also been detected at gamma-ray wavelengths by the Fermi Large Area Telescope (Fermi-LAT), and by very high energy gamma-ray Cherenkov telescopes. It is thought that due to the orientation of their jets, radio galaxies are detected less numerously at gamma-ray energies than blazars. Furthermore, only a small number of radio galaxies have been detected at gamma-ray energies though it is considered that others do as well. It is for these reasons that gamma-ray emitting radio galaxies, an interesting and elusive class of objects, are selected for investigation in this work. In order to reach the goal of better understanding diffuse processes, it is necessary to model the radio galaxy spectral energy distributions (SEDs). As AGN emission is variable with respect to time, it is critical to use simultaneously collected observations. Calculation of the SED based on simultaneous, multiwavelength data across the electromagnetic spectrum produces a reasonably accurate representation of the state of an object in a given time range. The gamma-ray emitting radio galaxies M 87, NGC 1275, Pictor A, and Centaurus A are selected here based on having been detected in very high energy gamma-rays by Cherenkov telescopes, as well as in other wavelengths. A uniquely consistent analysis approach is applied, in which each radio galaxy is analyzed the same way using simultaneously collected data. This approach sets it apart from other studies. Fermi-LAT raw data for each source in the sample is analyzed in time ranges which directly overlap the very high energy gamma-ray Cherenkov observations, as well as several other wavelength ranges. A synchrotron self-Compton (SSC) model is applied, which provides accurate treatment of synchrotron and inverse-Compton processes occurring in the jets of AGN, while estimating physical characteristics of the source. It is found that the spectra of M 87, NGC 1275, Pictor A, and Centaurus A can be well described by the same SSC model, producing values for the physical characteristics such as the doppler factor and magnetic field, which are relatively consistent with each other. In order to characterize the diffuse emission from dark matter self-annihilation, the radio galaxy SEDs are also fit with a dark matter model, resulting in an estimated dark matter particle mass of around 4.7 TeV which lies within predicted ranges. The highly dense regions near the black holes of AGN provide the optimal conditions for detecting these signatures. It is also found here that discrepancies between the expected emission and the observed emission in the spectra of some radio galaxies can be explained using the combined SSC and dark matter model. As emission from dark matter annihilation is expected to remain steady with respect to time, a key feature of this work is the novelty of the combined SSC and dark matter model, and the finding that dark matter characteristics may be revealed through similar multiwavelength analyses during future low emission states of the AGN. The radio galaxy sample is then extended to include all gamma-ray emitting radio galaxies detected by the Fermi-LAT, and a calculation of the core radio, total radio, and gamma-ray luminosities is followed through. A future step in extending this work would be to estimate the gamma-ray luminosity function of radio galaxies and their percent contribution to the total IGRB, based on the widely agreed upon assumption that a reasonable estimate of the gamma-ray luminosity function of a population can be attained by appropriately scaling its radio luminosity function, as gamma-ray luminosities and radio luminosities are strongly linearly correlated. This work has also provided the basis for such a calculation by outlining the theory and initial steps. It is the hope that the vast scope of the gathered data, its simultaneity, and the use of consistent analysis methods across the sample, will provide an improved foundation for a future calculation of the contribution of this population to the IGRB, as well as encourage stricter requirements for multiwavelength studies. / Der Ursprung, sowie die exakte Zusammensetzung des isotropischen Gammastrahlen-Hintergrunds (IGRB), sind trotz jahrelanger Studien über den Einfluss unaufgelöster extragalaktischer Objekte, nicht abschließend geklärt. Es wird für möglich gehalten, dass diffuse Prozesse, wie z.B. die Annihilation dunkler Materie, sowie bisher nicht detektierte Gammastrahlen-Emission aus aktiven Galaxiekernen (AGN), wie zum Beispiel Radiogalaxien, dazu beitragen. Radiogalaxien gehören zu der Gattung der Quellen, die stark im Radiowellenbereich emittieren. Einige dieser Galaxien wurden auch im Wellenlängenbereich von Gammastrahlung mittels des Fermi Large Area Telescope (Fermi-LAT) und für sehr energiereiche Gammastrahlung mittels Cherenkov-Detektoren nachgewiesen. Es wird davon ausgegangen, dass die kleinere Anzahl an nachgewiesenen Radiogalaxien im Gammastrahlenbereich, verglichen mit der Anzahl an nachgewiesenen Blazaren, auf die Orientierung ihrer Jets zurückzuführen ist. Des Weiteren wurde bisher nur eine kleine Anzahl an Radiogalaxien im Energiebereich der Gammastrahlung nachgewiesen, obwohl davon auszugehen ist, dass der Nachweis auch für weitere Galaxien möglich ist. Aus diesen Gründen werden Gammastrahlung emittierende Radiogalaxien, eine interessante und schwer auffindbare Klasse an Objekten, zur Untersuchung im Rahmen dieser Arbeit ausgewählt. Zur Verbesserung des Verständnisses diffuser Prozesse ist eine Modellierung der spektralen Energiedichteverteilung (SED) notwendig. Da die Emission von AGN zeitlich variiert, ist es wichtig simultan aufgezeichnete Daten für die Analyse zu verwenden. Die Berechnung der spektralen Energiedichteverteilung, basierend auf zeitgleich aufgezeichneten Daten für eine Vielzahl an Wellenlängen des elektromagnetischen Spektrums, liefert eine hinreichend genaue Beschreibung des Zustandes eines Objektes innerhalb eines gegebenen Zeitraumes. Diese Arbeit konzentriert sich auf die Gammastrahlung emittierenden Radiogalaxien M 87, NGC 1275, Pictor A und Centaurus A, da diese mittels Cherenkov-Teleskopen im Bereich hochenergetischer Gammastrahlung, sowie auch in anderen Wellenlängenbereichen, nachgewiesen wurden. Es wird eine, in dieser Form erstmals angewandte, konsistente Untersuchung durchgeführt, bei der jede Radiogalaxie auf identische Weise, mittels zeitgleich aufgezeichneter Daten, analysiert wird. Dieser Ansatz unterscheidet diese Arbeit von vergleichbaren Studien. Die Fermi-LAT Rohdaten für jede Quelle werden für die Zeiträume analysiert, in denen diese direkt mit der Beobachtung hochenergetischer Gammastrahlung durch Cherenkov-Teleskope, sowie darüber hinaus mit weiteren Wellenlängenbereichen, überlappen. Das Synchrotron Self-Compton (SSC) Modell wird der Analyse zu Grunde gelegt und ermöglicht eine akkurate Beschreibung, der im AGN Jet auftretenden, Synchrotron Prozesse und inversen Compton-Streuung, sowie die Abschätzung physikalischer Charakteristiken der Quelle. Es stellt sich heraus, dass die Spektren von M87, NGC 1275, Pictor A und Centaurus A mit demselben SCC Modell gut beschrieben werden können und relativ konsistente Werte für physikalische Größen, wie zum Beispiel den Doppler-Faktor oder die Magnetfeldstärke liefern. Zur genaueren Charakterisierung der aus der Annihilation dunkler Materie resultierenden diffusen Emission, werden die SED der Radiogalaxien zusätzlich mit einem Modell für dunkle Materie gefittet. Die daraus resultierende, geschätzte Teilchenmasse für dunkle Materie liegt mit 4.7 TeV innerhalb des vorhergesagten Bereiches. Die hochdichten Regionen in der Nähe der schwarzen Löcher des AGN liefern ideale Voraussetzungen zur Detektion dieser Signaturen. Des Weiteren wurde herausgefunden, dass etwaige Unterschiede zwischen der erwarteten und der beobachteten Emission in den Spektren einiger Radiogalaxien mittels einer Kombination aus SSC Modell und dunkler Materie Modell erklärt werden können. Unter der Annahme, dass die der Annihilation dunkler Materie zu Grunde liegende Emission zeitlich konstant bleibt, stellen zum einen die Kombination des SSC- und dunkler Materie Modells, sowie die Erkenntnis, dass Charakteristiken dunkler Materie durch ähnliche Multi-Wellenlängen-Experimente während zukünftiger, emissionsarmer Zustände gefunden werden können, die wesentlichen Ergebnisse dieser Arbeit dar. Das Sample der Radiogalaxien wird anschließend erweitert, so dass es alle vom Fermi-LAT detektierte und Gammastrahlung emittierende Radiogalaxien umfasst. Im Anschluss daran wird eine Berechnung der aus dem Kernbereich stammenden, und der totalen Radioluminosität, sowie der Gammastrahlungs-Luminosität durchgeführt. Ein künftiger Schritt zur Erweiterung dieser Arbeit wäre die Abschätzung der Gammastrahlungs-Luminositätsfunktion von Radiogalaxien und deren prozentualer Beitrag zum totalen IGRB, basierend auf der weitläufig akzeptierten Annahme, dass eine vernünftige Abschätzung der Gammastrahlungs-Luminositätsfunktion einer Population mittels einer angemessenen Skalierung ihrer Radio-Luminositätsfunktion erreicht werden kann, da die Gammastrahlungs-Luminosität und die Radioluminosität stark miteinander korrelieren. Diese Arbeit hat die hierfür benötigten Grundlagen für diese Art von Berechnung gelegt, indem sie die Theorie und die ersten Schritte darlegt. Es ist die Hoffnung, dass der große Umfang der zusammengetragenen Daten, deren Simultanität, und die Anwendung einer konsistenten Analysemethode für das gesamte Sample eine verbesserte Grundlage für zukünftige Berechnungen des Beitrages dieser Population zum IGRB leistet, sowie strengere Anforderung für Multi-Wellenlängen-Experimente.

No description available.

The work contained within this thesis Is made up primarily of two pieces Both address active galactic nuclei And the galaxies that live nearby The obscured fraction of the population Is the topic of one publication And the type-II fraction in the optical regime In chapter four this is the theme I research the vicinity overdensity Around radio galaxies in chapter three, you’ll see I reduce some spectra at redshift one But not all observations in the end got done With the spectra I have I do what I can As if all target observations had actually ran In the end I conclude with results and the theme of research to be done further downstream. The works contained herein addresses two major topics in extragalactic astrophysics, namely the Type-II AGN fraction and the Overdensity-Radio power relation. Quantifying the Type-II AGN fraction has been attempted by many works in many different observational regimes, finding rather contrasting results. Accretion onto supermassive black holes contributes between 5 per cent and 20 per cent of the luminosity of the Universe, and seems to be closely linked to star formation processes. The large uncertainty on this value is due to the ill-determined contribution from obscured accretion, namely the Type-II fraction. In Chapters 3 and 4 I address this issue from a theoretical standpoint in the X-ray regime and an observational standpoint in the optical regime respectively. In Chapter 3 I show how crude X-ray spectroscopy of partially obscured AGN can lead to catastrophic underestimations of the intrinsic X-ray luminosity of these sources. Acting over an entire population, these partial obscurers can produce an obscured AGN fraction which decreases as a function of observed luminosity. The results are consistent with observations in the X-ray vs. IR luminosity of AGN classes. In Chapter 4 I select a statistically significant sample of AGN from an unbiased 250μm galaxy sample. After spectroscopic classification I find the optical Type- II AGN fraction to be consistent across several decades in [OIII] luminosity, a common proxy for intrinsic AGN luminosity. I also investigate the relation of AGN activity to host galaxy mass, as well as star formation activity and star formation history. Probing the environments of protoclusters will help to constrain the models of structure formation in the Universe. Until now, no dataset has been big enough to probe the environments of high redshift radio galaxies at a statistical level; While many believe that the feedback processes of high luminosity radio jets will have a direct impact on star formation in the surrounding medium it has not been tested. In Chapter 2 I investigate this on an statistical level, finding no meaningful correlation between radio galaxy radio power and source overdensity in the vicinities of these sources. In Chapter 5 I discuss the reduction of a 24μm sample at redshift z ∼ 1 for direct comparison with a local 12μm sample. With only a fraction of the target sample being observed, no statistically significant results could be derived, but the objects are spectroscopically classified and spectroscopic redshifts are measured where possible. Correlations in the data set are investigated and the limitations of the sample selection strategy are discussed.

In this thesis, I use the new generation of radio interferometer along with X-ray observations to investigate the dynamics and energetics of radio-loud active galaxies which are key to understanding AGN feedback and the evolution of galaxies as a whole. I present new JVLA observations of powerful radio source and use innovative techniques to undertake a detailed analysis of JVLA observations of powerful radio galaxies. I compare two of the most widely used models of spectral ageing, the Kardashev-Pacholczyk and Jaffe-Perola models and also results of the more complex, but potentially more realistic, Tribble model. I find that the Tribble model provides both a good fit to observations as well as providing a physically realistic description of the source. I present the first high-resolution spectral maps of the sources and find that the best-fitting injection indices across all models take higher values than has previously been assumed. I present characteristic hot spot advance speeds and compare them to those derived from dynamical ages, confirming that the previously known discrepancy in speed remains present in older radio sources even when ages are determined at high spectral and spatial resolutions. I show that some previously common assumptions made in determining spectral ages with narrow-band radio telescopes may not always hold. I present results from a study of the powerful radio galaxy 3C223 at low frequencies with LOFAR to determine its spectrum on spatially small scales and tightly constrain the injection index, which I find to be consistent with the high values found at GHz frequencies. Applying this new knowledge of the low energy electron population, I perform synchrotron / inverse-Compton model fitting and find that the total energy content of the radio galaxy lobes increases by a factor greater than 2 compared to previous studies. Using this result to provide revised estimates of the internal pressure, I find the northern lobe to be in pressure balance with the external medium and the southern lobe to be overpressured. I go on to present the first large sample investigation of the properties of jets in Fanaroff and Riley type I radio galaxies (FR-I) at X-ray energies based on data from the Chandra archive. I explore relations between the properties of the jets and the properties of host galaxies in which they reside. I find previously unknown correlations to exist, relating photon index, volume emissivity, jet volume and luminosity, and find that the previously held assumption of a relationship between luminosities at radio and X-ray wavelengths is linear in nature when bona fide FR-I radio galaxies are considered. In addition, I attempt to constrain properties which may play a key role in determination of the diffuse emission process. I test a simple model in which large-scale magnetic field variations are primarily responsible for determining jet properties; however, we find that this model is inconsistent with our best estimates of the relative magnetic field strengths in my sample.

During the quasar era (redshifts between 1 and 3) Radio Galaxies (RGs) have been claimed to have substantially influenced the growth and evolution of large scale structures in the universe. In this dissertation I test the robustness of these exciting claims. In order to probe the impacts in more detail, good theoretical models for such RG systems are required. With this motivation, I seek to develop an essentially analytical model for the evolution of Fanaroff-Riley Class II radio galaxies both as they age individually and as their numbers vary with cosmological epoch. To do so, I first compare three sophisticated semi-analytical models for the dynamical and radio lobe power evolution of FR II galaxies, those given by Kaiser, Dennett-Thorpe & Alexander (1997, KDA), Blundell, Rawlings, & Willott (1999, BRW) and Manolakou & Kirk (2002, MK). I perform multi-dimensional Monte Carlo simulations leading to virtual radio surveys. The predictions of each model for redshift, radio power (at 151 MHz), linear size and spectral index are then compared with data. The observational samples are the low frequency radio surveys, 3CRR, 6CE and 7CRS, which are flux-limited and redshift complete. I next perform extensive statistical tests to compare the distributions of model radio source parameters and those of the observational samples. The statistics used are the 1-Dimensional and 2-Dimensional Kolmogorov-Smirnov (K-S) tests and the 4-variable Spearman partial rank correlation coefficient. I search for and describe the "best" parameters for each model. I then produced modifications to each of the three original models, and extensively compare the original and the modified model performances in fitting the data. The key result of my dissertation is that using the Radio Luminosity Function of Willott et al. (2001) as the redshift birth function of radio sources, the KDA and MK models perform better than the BRW models in fitting the 3CRR, 6CE and 7CRS survey data when using K-S based statistical tests, and the KDA model provides the best fits to the correlation coefficients. However, no pre-existing or modified model can provide adequate fits for the spectral indices. I also calculate the volume fraction of the relevant universe filled by the generations of radio galaxies over the quasar era. This volume filling factor is not as large as estimated earlier. Nonetheless, the allowed ranges of various model parameters produce a rather wide range of astrophysically interesting relevant volume fraction values. I conclude that the expanding RGs born during the quasar era may still play significant roles in the cosmological history of the universe.

No description available.

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. / 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.