This thesis presents studies of cosmic populations of extragalactic radio sources. The problems selected for this thesis are 1) the derivation of constraints on the emergence of new sub-mJy populations at flux density below about 1mJy (at1.4 GHz) paying careful attention to including sources with low surface brightness and counting sources rather than components 2) development of a new method to estimate the asymmetry in the large scale galaxy environment with respect to the axes of extended radio sources and use this to examine for evidence of impact of the environment on the morphology of radio sources. The studies presented herein have been carried out using the Australia Telescope Low Brightness Survey (ATLBS), which is a sensitive radio survey at 1.4 GHz, imaging 8.42 square degrees of the sky along with accompanying optical observations of the same region. There are multiple populations of extragalactic radio sources in the cosmos. These consist of populations of powerful radio-loud quasars and radio galaxies to populations of weaker radio sources such as star-forming galaxies. These populations of radio sources show evidence of evolution with cosmic epoch. Because the radio galaxy phenomenon and the AGNs at the centers of their host galaxies may influence the evolution of the galaxy via feedbacks, examinations of these source populations over cosmic time are a necessary complementary study to understanding the process of galaxy formation and in general, cosmology. Below we give brief introduction to the problems studied in this thesis. Sub-mJy Radio Source Counts Radio source counts, which have historically been a key probe of cosmology, now represent a measure of cosmological evolution in radio source populations. Currently, the estimation of source counts at sub-mJy flux density as well as the nature and evolution of these sources is undetermined. At flux densities ≤1.0 mJy a ‘flattening’ of normalized differential source counts has been widely reported in literature( Windhorst et al.(1985),Hopkins et al.(2003),Huynh et al.(2005) and references therein). The flattening is observed as an apparent change of slope for the normalized differential source counts from ∼0.7 at5.0 −100.0 mJy to about 0.4 in the 0.25 −5.0 mJy range. Attempts to understand the nature of the sub-mJy population have arrived at discordant results and identify the sub-mJy sources with different populations: starburst galaxies(Condon(1989), Benn et al. (1993), Huynhet al. (2005)), early type galaxies (Gruppioniet al., 1999),low(radio) luminosity activegalactic nuclei(AGNs)(Huynh et al.,2008) or a mixture of these. Due to unavailability of spectroscopically complete samples of hosts of sub-mJy sources, the exact nature of the sub-mJy radio source population is currently uncertain. However, the presence of a population which emerges at sub-mJy flux density and is different from the AGN-dominated radio source population is not in doubt. The studies in the literature are inconsistent in identifying the precise location of the emergence of flattening in counts at sub-mJy flux density. Several studies show that the source counts are consistent with a continuation in the slope of the differential counts below mJy flux density (Prandoniet al.(2001) and Subrahmanyan et al.(2010)). The scatter in the sub-mJy counts from different studies may be because of the relatively small areas covered by deep surveys(in many cases, a single pointing of an interferometric array) which may have relatively large errors arising from large scale clustering in the spatial distribution of cosmic radio sources(however the study by Condon (2007) concludes that the scatter in the source counts stems from variations in corrections and sensitivity in different studies)In contrast, wide-field surveys may not reach the depth to probe sub-mJy counts. Another reason is the correction applicable to the observed source counts necessary to estimate the true source counts; these are especially pertinent at low flux densities. To resolve these is-sues, a survey which combines the attributes of wide spatial coverage as well as excellent sensitivity and a procedure which accounts for the biases in estimation of the sub-mJy source counts is needed. In conclusion, accurate measurements of the source counts at sub-mJy flux densities are needed to correctly estimate the cosmic evolution of radio sources. Environments of Extended Radio Sources Another issue of importance in the study of extragalactic radio sources is their interaction with their environments. The gas environments in which radio sources reside and evolve ought to have an influence on the morphology of the radio sources. This has been shown in many case studies where the radio structures have been compared with the X-ray gas environments (Blanton et al. (2011); Boehringer et al.(1993)). Studies of the optical environments of radio galaxies have also been carried out previously (Longair & Seldner, 1979; Yee & Green, 1984; Hill & Lilly, 1991; Zirbel, 1997). The motivation behind these studies has been to examine differences between different classes of radio sources, the evolution of environments with cosmic epoch as well as the possibility of identifying clusters/groups of galaxies using radio sources as a tracer(Wing &Blanton, 2011). Many previous studies have found that the environments of FRI/FRII sources are different and are dependent on the cosmic epoch. FRI sources, typically, are found in rich environments. FRII sources in the local universe are generally hosted by field galaxies, but at higher red shifts are found in richer environments(Hatch et al.,2011;Best et al.,2003;Overzier et al.,2008). However, there have been fewer studies that relate the richness of the environments and morphological asymmetries of radio galaxies. Earlier investigations by Subrahmanyan et al. (2008) and Safouris et al.(2009) are noteworthy in this regard where the radio structures of two giant radio galaxies were examined in the context of the large-scale galaxy distributions in their vicinity(also see Chen et al.(2012) and references therein). The study was also used to infer properties of the ambient thermal gas medium in which the structures evolved. Clear correlations between structural asymmetries and associated extended emission-line gas were also found for radio galaxies that have relatively smaller sizes of a few hundred kpc(McCarthy et al., 1991). Thesis Work To progress the field in the problems highlighted above, the following work has been done in this thesis. Radio Imaging of ATLBS Survey To characterize the cosmic evolution of radio sources and their properties, observations and imaging of faint radio sources is essential. The Australia Telescope Low Brightness Survey(ATLBS), which has been used in the studies presented in this thesis, has been designed specifically to image diffuse radio emission to relatively high red shifts(z ∼1−1.5). Therefore obtaining good surface brightness sensitivity was a prime objective in planning the radio observations and in imaging the data obtained from these observations. This requires a nearly complete synthesized aperture and observations of a representative patch of the extra galactic sky. These requirements have been fulfilled in ATLBS survey, which has excellent uv coverage, especially at short spacings, and images a region off the galactic plane that is devoid of strong radio sources. The observations were carried out for two adjacent fields, designated as A and B with their centers at RA:00h 35m 00s,DEC:−67◦00 00 and RA:00h 59m 17s,DEC:−67◦00 00 ,in the 20 cm band, with a center frequency of1388MHz,infullpolarization mode. The radio data was imaged by using techniques such as multi-frequency deconvolution and self-calibration to make two mosaics of region A and B which are free of artefacts. These high-resolution radio images(with beamFWHM of 6 “)of the ATLBS survey regions cover 8.42 square degrees sky area with rms noise 72 µJy beam−1 and are of exceptional quality in that there are no imaging errors or artifacts above the thermal noise over the entire field of view. The images have excellent surface brightness sensitivity and hence provide good representation of extended emission components associated with radio sources. Optical Imaging of ATLBS Survey The ATLBS survey region has been also observed in SDSS r band, specifically for providing information about the galaxies hosting radio sources observed in ATLBS survey as well as galaxies in the neighbourhood of the radio sources. The optical observations were carried out using the CTIO 4 meter Blanco Telescope in Chile and using theMOSAICIIimager,whichisamosaicof8CCDs. In total, 28 optical images were created from the optical data. Each image was formed from a set of 5 dithers, using which spurious sources in the images were rejected. The final images are complete down to a magnitude of 22.75. Radio Source Counts Using the sensitive radio and optical images, a study of radio source counts was carried out. This study made use of some novel strategies and algorithms to generate a source list and correct it for various biases to obtain the radio source counts. More specifically, care was taken to identify sources with low surface brightness by making use of low resolution images for initial identification, and using multiple indicators (including optical images) to identify components of sources. The blending issues inherent in using low resolution images has been avoided using higher resolution images to identify blended sources. Thus, use of low resolution images( beam FWHM =50”′) almost completely removes effects of resolution bias and the use of high resolution images avoids blending issues. These strategies, together with use of optical images to locate candidate galaxy hosts and a careful visual examination of resolved and complex sources instead of automated classification ensures that the ATLBS catalog is a ‘source catalog’ as opposed to a ‘component catalog’. The distinction between ‘sources’ (which are single sources) as opposed to components(parts of a single source appearing separate) is crucial in estimating the true source counts. The source list was used toestimatetheradiosourcecountsdownto0.4 mJy. Comparing the counts with previous work shows that the ATLBS counts are systematically lower and the upturn in sub-mJy source counts has not been found down to the noise limited flux densities probed. The systematically low counts for ATLBS relative to most previous studies are attributed to the ATLBS counts representing sources as opposed to components, as well as corrections for noise bias as well as clustering effects that may affect source counts derived from the small sky coverage typical of deep surveys. This study also demonstrates the substantial difference in counts that result from using component catalogs as opposed to source catalogs: at 1 mJy flux density component counts may be as much as 50% above true source counts. This implies that automated image analysis for counts may be dependent on the ability of the imaging to reproduce connecting emission with low surface brightness as well as the ability of the algorithm to recognize sources, which require that source finding algorithms effectively work with multi-resolution and multi-wavelength data. Galaxy Environments of Extended Radio Sources in ATLBS Survey A study of the galaxy environments of the extended sources in the ATLBS survey was carried out using the optical images. This study of the environments of radio sources from the ATLBS survey is restricted to those that are extended and hence to a subset of the ATLBS-ESS(Extended Source Sample) sources. Briefly, the ATLBS-ESS subsample consists of 119 radio sources that have angular size ex-ceeding0’.5. Applying a red shift cut(to exclude sources with high red shifts whose optical environment may be beyond the depth of the optical images) as well as other constraints(such as availability of optical magnitudes of the host galaxy), a sub-sample of 43 sources was formed, including sources of diverse radio morphologies(FRI/FRII, WATs and HTs)as well as7 radio sources which are highly asymmetric in their radio morphology. For these sources, where no spectroscopic data was available, a red shift estimate was obtained from a magnitude-red shift relation derived from other sources in the ATLBS survey. Using the optical images convolved with a matched filter(following the prescription from Postman et al. (1996))consisting of a radial and magnitude filter, smoothed maps were formed for each source in the sample. These give the likelihood of a cluster being present in a given position in the map (in this case the location of interest being the position of the radio source in the map). Further, five parameters were defined in this study, which give estimates of the angular anisotropy of galaxy density around the axis of the radio source. This method used to quantify environmental asymmetry for the study presented in the thesis is new. The parameters defined thus were used to examine the environments of radio sources in the sample over a wide range in red shift. Specifically a comparison of FRI/FRII environments was made in two different red shift regimes(above and below z = 0.5) and it was found that the FRI and FRII sources inhabit environments of similar richness at low and high red shifts, with no evidence for red shift evolution. The WAT and HT sources were(as expected from earlier studies in literature)found in the most dense environments. Examination of the anisotropy parameters for the asymmetric radio sources clearly showed the influence environment has on radio source morphology, specifically in that the higher density of galaxies was found on the shorter side of the radio sources in almost all cases. Images and Other Resources The radio and optical images are an excellent resource for examining with auto-mated algorithms for source finding, parameter fitting, and morphological classification, and as a resource for testing such algorithms that would be used on upcoming all-sky continuum surveys with the LOFAR and ASKAP/SKA. The techniques and methods developed and presented in the thesis may be used in future studies of radio source populations.

L'objectif principal de mon travail de thèse est de comprendre les processus qui agissent sur la poussière pendant le couplage entre le milieu interstellaire galactique et le milieu intra-amas. Ce processus est d'intérêt particulier dans les phénomènes violents comme les interactions galaxie-galaxie ou le "Ram Pressure Stripping" causé par la chute d'une galaxie vers le centre de l'amas.Initialement, je me suis concentré sur le problème de la destruction de la poussière et le processus de chauffage, en re-visitant les modèles présents en littérature. J'ai particulièrement insisté sur les cas des environnements extrêmes comme le gaz chaud de type coronale (e.g., IGM, ICM, HIM) et les chocs interstellaires générés par les supernovae. Sous ces conditions les petits grains sont détruits rapidement et les gros grains sont chauffés par les collisions avec les électrons énergétiques, en rendent la distribution spectral d'énergie de la poussière très différente de ce qu'on observe dans le milieu interstellaire diffus.Pour tester nos modèles j'ai les appliqués au cas d'une galaxie en interaction, NGC 4438. Les données Herschel de cette galaxie indiquent la présence de la poussière avec une température plus élevée de ce qu'on s'attendait.Avec une analyse à plusieurs longueurs d'onde on montre que cette poussière chaude semble être dans un gaz ionisé et chaud et donc subir à la fois le chauffage collisionnel et la destruction des petits grains.De plus, je me suis focalisé sur l'énigme de longue date à propos de la différence entre les échelles de temps de destruction et formation de la poussière dans la Voie Lactée. Basées sur l'efficacité de destruction de la poussière dans les chocs interstellaires, les estimations précédentes portent à une durée de vie de la poussière plus courte que l'échelle de temps typique de sa formation dans les étoiles AGB. En utilisant un modèle de poussière récent et les dernières estimations pour l'évolution de la poussière, on a réévalué la durée de vie de la poussière dans notre Galaxie. Finalement, j'ai tourné mon attention au phénomène de "Ram Pressure Stripping''. La galaxie ESO 137-001 représente un des meilleurs cas pour étudier cet effet. Sa longue queue H2 intégrée dans une queue de gaz chaud et ionisé soulève des questions sur son possible arrachement de la galaxie ou sa formation en aval dans la queue. Basé sur des récentes simulations numériques, j'ai montré que la formation des molécules de H2 sur la surface des grains dans la queue est un scénario viable. / The main goal of my PhD study is to understand the dust processing that occurs during the mixing between the galactic interstellar medium and the intracluster medium. This process is of particular interest in violent phenomena such as galaxy-galaxy interactions or the "Ram Pressure Stripping'' due to the infalling of a galaxy towards the cluster centre.Initially, I focus my attention to the problem of dust destruction and heating processes, re-visiting the available models in literature. I particularly stress on the cases of extreme environments such as a hot coronal-type gas (e.g., IGM, ICM, HIM) and supernova-generated interstellar shocks. Under these conditions small grains are destroyed on short timescales and large grains are heated by the collisions with fast electrons making the dust spectral energy distribution very different from what observed in the diffuse ISM.In order to test our models I apply them to the case of an interacting galaxy, NGC 4438. Herschel data of this galaxy indicates the presence of dust with a higher-than-expected temperature.With a multi-wavelength analysis on a pixel-by-pixel basis we show that this hot dust seems to be embedded in a hot ionised gas therefore undergoing both collisional heating and small grain destruction.Furthermore, I focus on the long-standing conundrum about the dust destruction and dust formation timescales in the Milky Way. Based on the destruction efficiency in interstellar shocks, previous estimates led to a dust lifetime shorter than the typical timescale for dust formation in AGB stars. Using a recent dust model and an updated dust processing model we re-evaluate the dust lifetime in our Galaxy. Finally, I turn my attention to the phenomenon of "Ram Pressure Stripping''. The galaxy ESO 137-001 represents one of the best cases to study this effect. Its long H2 tail embedded in a hot and ionised tail raises questions about its possible stripping from the galaxy or formation downstream in the tail. Based on recent hydrodynamical numerical simulations, I show that the formation of H2 molecules on the surface of dust grains in the tail is a viable scenario.

Utrahochenergetische kosmische Strahlung (ultra-high-energy cosmic rays -- UHECR) besteht aus ionisierten Atomkernen mit den höchsten Teilchenergien, die je gemessen wurden. Zwar wurden die Quellen von UHECRs noch nicht eindeutig identifiziert, doch gibt es deutliche Anzeichen, dass sie extragalaktisch sind. Um die Beobachtungen zu interpretieren, wird ein Modell der Wechselwirkungen mit Photofeldern sowohl in der Quelle als auch während der extragalaktischen Propagation benötigt. Bei diesen Wechselwirkungen werden sekundäre Neutrinos erzeugt. Diese Dissertation behandelt Modelle der Quellen von UHECRs und die damit verbundene Produktion von Neutrinos sowohl in den Quellen als auch während der Propagation. Dafür wurde ein neuer Code, PriNCe, für die Propagation von UHECRs entwickelt. Dieser Code wird in einem umfangreichen Parameterscan für ein generisches Quellenmodell angewendet, welches mit dem Spektralindex, der maximalen Rigidität, der kosmologischen Quellenverteilung und der chemischen Komposition als freie Parameter definiert ist. Dabei wird der Einfluss von verschiedenen Photodisintegrations- und Luftschauermodellen auf die erwarteten Eigenschaften der Quellen demonstriert. Der Fluss kosmogenischer Neutrinos, der sich daraus robust vorhersagen lässt, liegt außerhalb der Reichweite aller derzeit geplanten Neutrinodetektoren. GRBs als mögliche Quellen von UHECRs werden im Multi-Collision Internal-Shock Modell simuliert, welches die Abhängigkeit der Strahlungsprozesse von den verschiedenen Dissipationsradien im Plasmajet berücksichtigt. Für dieses Modell wird der Effekt demonstriert, den verschiedene Annahmen über die anfängliche Verteilung des Plasmajets und das hydrodynamische Modell auf die resultierende UHECR- und Neutrinosstrahlung haben. Für den Gammastrahlenblitz GRB170817A, welcher zusammen mit einem Gravitationswellensignal beobachtet wurde, werden Vorhersagen für den Neutrinofluss und ihre Abhängigkeit vom Beobachtungswinkel gemacht. / Ultra-high-energy cosmic rays (UHECRs) are the most energetic particles observed in the Universe. While the astrophysical sources of UHECRs have not yet been uniquely identified, there are strong indications for an extragalactic origin. The interpretation of the observations requires both simulations of UHECR acceleration and energy losses inside the source environment as well as interactions during extragalactic propagation. Due to their extreme energies, UHECR will interact with photons in these environments, producing a flux of secondary neutrinos. This dissertation deals with models of UHECR sources and the accompanying neutrino production in the source environment and during extragalactic propagation. We have developed a new, computationally efficient code, PriNCe, for the extragalactic propagation of UHECR nuclei. The PriNCe code is applied for an extensive parameter scan of a generic source model that is described by the spectral index, the maximal rigidity, the cosmological source evolution and the injected mass composition. In this scan, we demonstrate the impact of different disintegration and air-shower models on the inferred source properties. A prediction for the expected flux of cosmogenic neutrinos is also derived. GRBs are discussed as specific UHECR source candidates in the multi-collision internal-shock model. This model takes the radiation from different radii in the GRB outflow into account. We demonstrate how different assumptions about the initial setup of the jet and the hydrodynamic collision model impact the production of UHECRs and neutrinos. Motivated by the multi-messenger observation of GRB170817A, we discuss the expected neutrino production from this GRB and its dependence on the observation angle. We show that the neutrino flux for this event is at least four orders of magnitude below the detection limit for different geometries of the plasma jet.

[pt] Em 2013, o IceCube Neutrino Observatory, localizado no Polo Sul, descobriu um fluxo de neutrinos astrofísicos com energias de PeV. Mais tarde, descobriu-se que este fluxo se estendia até pelo menos aproximadamente 10 TeV. Apesar de muitos esforços desde então, determinar as suas fontes permanece sendo um dos maiores desafios na comunidade de astrofísica. Nesta dissertação, investigamos possíveis fontes através de uma abordagem multimensageira bem motivada. Em qualquer mecanismo para a produção de neutrinos cósmicos, obrigatoriamente há produção simultânea de raios gama com energias comparáveis. Ao contrário de neutrinos, que atravessam o Universo ilesos, raios gama de altas energias sofrem interações com fótons de fundo em um processo de degradação de energia conhecido como cascata eletromagnética. Na Terra, eles contituem o fundo extragalático de raios gama difuso (EGB), medido com precisão pelo Fermi Gamma-ray Space Telescope entre GeV–TeV. Realizando uma análise conservativa, quantitativa e multimensageira, encontra-se uma tensão de maior ou aproximadamente 3delta (possivelmente chegando a aproximdamente 5 delta) entre os dados do IceCube e do EGB, apontando para a exitência de uma nova classe de aceleradores cósmicos de alta energia, como, por exemplo, fontes opacas para raios gama. / [en] In 2013, the IceCube Neutrino Observatory, located at the South Pole, discovered a flux of astrophysical neutrinos with PeV energies, later found to extend down to at least approximately 10 TeV. Despite many efforts since then, determining their sources remains one of the most daunting challenges in the astrophysics community. In this dissertation, we investigate possible sources via a well-motivated multimessenger approach. In any production mechanism of cosmic neutrinos, there must also be a simultaneous production of gamma-rays withcomparable energies. Unlike neutrinos, which travel unscathed throughout the Universe, high energy gamma-rays undergo interactions with background photons in an energy-degrading process known as electromagnetic cascade. At the Earth, they constitute the diffuse extragalactic gamma-ray background (EGB), precisely measured by the Fermi Gamma-ray Space Telescope in the GeV–TeV range. By performing a conservative, quantitative, multimessenger analysis, we find greater than a or approximately to 3 delta (possibly as large as approximately 5 delta) tension between IceCube and EGB data, pointing towards the existence of a new class of high energy cosmic accelerators, such as gamma-ray-opaque sources.

In dieser Doktorarbeit wurden im Rahmen des MAGIC Experimentes neue Datenanalysemethoden implementiert, die sich insbesondere fuer die Analyse von Ereignissen niedriger Gammastrahlungsenergie eignen. Die Methoden konnten erfolgreich in Monte Carlo Studien getestet und auf Beobachtungsdaten des Krebsnebels und der extragalaktischen Gammastrahlungsquelle PG1553+113 angewandt werden. Diese Methoden reichen von ''image cleaning'' Techniken und der Nutzung neuer Bildparameter bis zu fortgeschrittenen g/h-Separations- und Energieabschaetzungsverfahren. Zum ersten Mal wurden die Vorteile von Klassifikations- und Regressionsbaeumen in der Gamma-Astrophysik ausgenutzt, um existierende klassische Methoden zu verbessern. Die Analyse - getestet an Monte Carlo Daten - bewies ihre Zuverlaessigkeit bei der Untersuchung der Gammastrahlungsemission des Krebsnebels, wobei ein hochsignifikanter Exzess im Energiebereich unterhalb 100 GeV in nur 1.7 h nachgewiesen werden konnte. Die Analyse von Daten des BL Lac Objekts PG1553+113 ergab signifikante Exzesse fuer Beobachtungen in den Jahren 2005 und 2006. Das kombinierte alpha-Histogramm zeigt ein Signal mit einer Signifikanz, die 8 sigma ueberschreitet. Bei der weiteren Analyse konnte ein differentielles Energiespektrum fuer die kombinierten Daten aus den Jahren 2005 und 2006 erstellt werden. Der integrale Fluss oberhalb von 200 GeV wurde wie folgt bestimmt: F(> 200 GeV) = (1.7+-0.3) 10^(-12)/(cm^2 s), der spektrale Index betraegt Gamma = 3.6+-0.3. Dieses Spektrum konnte daraufhin verwendet werden, um die (unbekannte) Rotverschiebung von PG1553+113 auf z / In this thesis new data analysis methods for the MAGIC experiment were implemented, which are especially suited for the investigation of low energy gamma-ray events. They were successfully tested by means of Monte Carlo studies and applied to observational data of the Crab Nebula and of the extragalactic gamma-ray source PG1553+113. These methods extend from image cleaning techniques and the utilization of new image parameters to sophisticated g/h-separation and energy estimation approaches. For the first time in gamma-ray astrophysics the advantages of classification and regression trees were exploited in order to improve existing `classical'' methods. The analysis procedure - tested on Monte Carlo data - was demonstrated to be reliable in the investigation of the Crab Nebula gamma-ray emission yielding a significant excess in the energy range below 100 GeV in only 1.7 h observation time. The analysis of data taken on the BL Lac PG1553+113 yielded significant excesses for both years 2005 and 2006. The combined alpha histogram shows a signal in excess of 8 sigma. In the further analysis a spectrum could be derived for the combined data sets of 2005 and 2006. The integral flux above 200 GeV could be derived as F(> 200 GeV) = (1.7+-0.3) 10^(-12)/(cm^2 s), the power-law index was measured to be Gamma = 3.6+-0.3. This spectrum was used to constrain the redshift z of PG1553+113 with the result z

No description available.

This PhD thesis, written in english, studies the non-Gaussianity (NG) of extragalactic foregrounds to the Cosmic Microwave Background (CMB), the latter being one of the golden observables of today's cosmology. In the last decade has emerged research for deviations of the CMB to the Gaussian law, as they would discriminate the models for the generation of primordial perturbations. However the CMB measurements, e.g. by the Planck satellite, are contaminated by several foregrounds. I studied in particular the extragalactic foregrounds which trace the large scale structure of the universe : radio and infrared point-sources and the thermal Sunyaev-Zel'dovich effect (tSZ). I hence describe the statistical tools to characterise a random field : the correlation functions, and their harmonic counterpart : the polyspectra. In particular the bispectrum is the lowest order indicator of NG, with the highest potential signal to noise ratio (SNR). I describe how it can be estimated on data, accounting for a potential mask (e.g. galactic), and propose a method to visualise the bispectrum, which is more adapted than the already existing ones. I then describe the covariance of a polyspectrum measurement, a method to generate non-Gaussian simulations, and how the statistic of a 3D field projects onto the sphere when integrating along the line-of-sight. I then describe the generation of density perturbations by the standard inflation model and their possible NG, how they yield the CMB anisotropies and grow to form the large scale structure of today's universe. To describe this large scale structure, I present the halo model and propose a diagrammatic method to compute the polyspectra of the galaxy density field and to have a simple and powerful representation of the involved terms. I then describe the foregrounds to the CMB, galactic as well as extragalactic. I briefly describe the physics of the thermal Sunyaev-Zel'dovich effect and how to describe its spatial distribution with the halo model. I then describe the extragalactic point-sources and present a prescription for the NG of clustered sources. For the Cosmic Infrared Background (CIB) I introduce a physical modeling with the halo model and the diagrammatic method. I compute numerically the 3D galaxy bispectrum and produce the first theoretical prediction of the CIB angular bispectrum. I show the contributions of the different terms and the temporal evolution of the galaxy bispectrum. For the CIB angular bispectrum, I show its different terms, its scale and configuration dependence, and how it varies with model parameters. By Fisher analysis, I show it allows very good constraints on these parameters, complementary to or better than those coming from the power spectrum. Finally, I describe my work on measuring NG. I first introduce an estimator for the amplitude of the CIB bispectrum, and show how to combine it with similar ones for radio sources and the CMB, for a joint constraint of the different sources of NG. I quantify the contamination of extragalactic point-sources to the estimation of primordial NG ; for Planck it is negligible for the central CMB frequencies. I then describe my measurement of the CIB bispectrum on Planck data ; it is very significantly detected at 217, 353 and 545 GHz with SNR ranging from 5.8 to 28.7. Its shape is consistent between frequencies, as well as the intrinsic amplitude of NG. Ultimately, I describe my measurement of the tSZ bispectrum, on simulations and on Compton parameter maps estimated by Planck, validating the robustness of the estimation thanks to realist foreground simulations. The tSZ bispectrum is very significantly detected with SNR~200. Its amplitude and its scale and configuration dependence are consistent with the projected map of detected clusters and tSZ simulations. Finally, this measurement allows to put a constraint on the cosmological parameters : sigma_8*(Omega_b/0.049)^0.35 = 0.74+/-0.04 in agreement with other tSZ statistics.

Au cours des dernières décennies, l’astronomie infrarouge a changé notre point de vue au sujet de l’évolution des galaxies, en particulier à de grandes distances. Nous avons accès à une grande variété d’informations physiques grâce au domaine spectral infrarouge. Toutefois, les limites de diffraction des instruments infrarouges et l’existence d’un grand nombre de sources font de l’identification individuelle des galaxies une tâché difficile. La première partie de cette thèse est consacrée à Résoudre le fond extragalactique infrarouge avec l’observatoire spatial Herschel, à, l’aide de simulations réalistes, correspondant aux images les plus profondes jusqu’ici obtenues en infrarouge lointain. Nous avons étudié l’origine du bruit de confusion dans les images GOODS-Herschel et résolu une partie de fond cosmique infrarouge en galaxies individuelles. De nouvelles techniques ont été développées pour prédire les flux en infrarouge lointain à partir de la connaissance préalable des positions, décalages spectraux et densités de flux des sources dans l’infrarouge moyen. Les images simulées ont été construites en utilisant les flux prédits afin d’évaluer le rôle du bruit local de confusion et d’identifier des sources individuelles. La deuxième partie de la thèse concerne l’étude de la Destruction de grains de poussières par des jets vus en radio. Nous avons étudié les effets des noyaux actifs de galaxies dans le milieu interstellaire, en particulier le mécanisme qui donne lieu à la région des raies étroites dans les galaxies de type Seyfert. Des spectres en infrarouge proche à fente longue a ont été enregistrés sur un ensemble de galaxies Seyfert de type 2 afin de mesurer les raies d’émission de ([Fe II], [P II] et Paβ) qui révèlent la destruction de poussières par les ondes de choc produites par les jets radio. Nous avons constaté que le mécanisme dominant l’ionisation près du noyau des galaxies Seyfert est le champ de rayonnement produit par l’activité du trou noir. Dans la partie extérieure de la région des raies étroites, des ondes de choc induites par des jets de radio contribuent également au budget énergétique du milieu interstellaire et à la destruction des grains de poussière. Cette thèse s’est déroulée en co-encadrement au Service d’Astrophysique du CEA-Saclay et au Département d’Astronomie de l’Université de Concepción, au Chili. / During the last decades, infrared astronomy has changed our view about the evolution of galaxies, especially at large distances. We have access to large variety of physical information in the infrared bands. However, diffraction limits of the infrared instruments and the existence of a large number of sources makes individualization of galaxies a difficult task. The first part of this thesis is entitled Resolving the Cosmic Infrared Background with the Herschel Space Observatory where, by the use of far-infrared realistic simulations of the deepest infrared images of the Universe, we have studied the origin of the confusion noise in the GOODS-Herschel images and resolved a substantive part of the Cosmic Infrared Background into individual galaxies. New techniques were developed to predict the fluxes in the far-infrared from prior knowledge in the mid-infrared. Mock images were built using those predicted fluxes to evaluate the role of local confusion noise and identify individual sources. The second part of the thesis concerns the study of the Destruction of dust grains by radio jets. We study the effects of active galactic nuclei in the insterstellar medium, in particular in the mechanism that gives rise to the narrow-line region in Seyfert galaxies. Long-slit near-Infrared spectra of a set of type-2 Seyfert galaxies were taken to measure diagnostic emission lines ([Fe II], [P II] and Paβ) that reveal the destruction of dust grains due to the shock waves produced by the radio jets. We found that the dominant mechanism of ionization close to the nuclei of the Seyfert galaxies is the radiation field produced by the back hole activity. In the outer part of the narrow-line region, shock waves induced by the radio jets also contribute to the energy budget of the interstellar medium and sputter the dust grains. This was a co-advising thesis performed in the Service d’Astrophysique CEA-Saclay and the Astronomy Department of the University of Concepción, Chile. / Durante las últimas décadas, la astronomía infrarroja ha cambiado nuestra visión sobre la evolución de galaxias, en especial revelando que a grandes distancias (z >1) las galaxias individuales son típicamente Galaxias Infrarrojas Ultraluminosas (cuyas siglas en inglés son ULIRGs por Ultraluminous Infrared Galaxies, 1012 < Lbol < 1013 L⊙). Actualmente tenemos acceso a una gran variedad de información física basada en la emisión en bandas espectrales infrarrojas (IR), radiación que en el caso de las galaxias es producida en su mayoría por granos de polvo. Sin embargo, el límite de difracción de los instrumentos infrarrojos junto con el gran número de fuentes de emisión hace de la individualización de galaxias una tarea difícil. La primera parte de esta tesis se titula Resolviendo el Fondo Cósmico Infrarrojo con el Observatorio Espacial Herschel donde, con el uso de simulaciones realistas de las imágenes más profundas del Universo, hemos estudiado el origen del ruido de confusión en las imágenes GOODS-Herschel y resuelto en galaxias individuales una parte sustantiva del Fondo Cósmico Infrarrojo. Nuevas técnicas fueron desarrolladas para predecir los flujos en el infrarrojo lejano a partir del conocimiento a priori en el infrarrojo medio. Las imágenes simuladas fueron construidas usando esos flujos predichos y con ellos evaluar el rol del ruido de confusión local así como identificar fuentes individuales. La segunda parte de la tesis trata del estudio sobre la Destrucción de granos de polvo por chorros en ondas de radio. Este proyecto que se concentró en la observación de galaxias Seyfert y ULIRGS y apunta a entender mejor el ciclo de vida del polvo al estudiar la destrucción de granos en galaxias con nucleos activos y los efectos de la actividad de estas últimas en el medio interestelar, en particular en el mecanismo que da origen a la región de líneas de emisión angostas en las galaxias Seyfert. Se obtuvo espectros infrarrojos de rendija larga de galaxias Seyfert del tipo 2 para medir líneas de emisión ([Fe II], [P II] y Paβ) las cuales revelan la destrucción de granos de polvo debido a las perturbaciones de las ondas de choque producidas por chorros detectados en ondas de radio. Hemos encontrado que el mecanismo dominante de la ionización cerca de los núcleos de las galaxias Seyfers es el campo de radiación producido por la actividad del agujero negro central. En la parte externa de la región de líneas de angostas, las ondas de choque inducidas por los chorros en radio también contribuyen al balance energético del medio interestelar y desintegran los granos de polvo. Esta fue una tesis de co-tutela llevada a cabo en el Departamento de Astronomía de la Universidad de Concepción y en el Service d’Astrophysique del Commissariat á l’Énergie Atomique (CEA), Francia

Cette thèse, écrite en anglais, étudie la non-Gaussianité (NG) des avant-plans extragalactiques au fond de rayonnement fossile (FDC), celui-ci étant une des observables de choix de la cosmologie actuelle. Ces dernières années a émergé la recherche de déviations du FDC à la loi Gaussienne, car elles permettraient de discriminer les modèles de génération des perturbations primordiales. Cependant les mesures du FDC, e.g. par le satellite Planck, sont contaminées par différents avant-plans. J'ai étudié en particulier les avant-plans extragalactiques traçant la structure à grande échelle de l'univers: les sources ponctuelles radio et infrarouges et l'effet Sunyaev-Zel'dovich thermique (tSZ). Je décris donc les outils statistiques caractérisant un champ aléatoire : les fonctions de corrélations, et leur analogue harmonique : les polyspectres. En particulier le bispectre est l'indicateur de plus bas ordre de NG avec le plus fort rapport signal sur bruit (SNR) potentiel. Je décris comment il peut être estimé sur des données en tenant compte d'un masque (e.g. galactique), et propose une méthode de visualisation du bispectre plus adaptée que les préexistantes. Je décris ensuite la covariance d'une mesure de polyspectre, une méthode pour générer des simulations non-Gaussiennes, et comment la statistique d'un champ 3D se projette sur la sphère lors de l'intégration sur la ligne de visée. Je décris ensuite la genèse des perturbations de densité par l'inflation standard et leur possible NG, comment elles génèrent les anisotropies du FDC et croissent pour former la structure à grande échelle de l'univers actuel. Pour décrire cette dite structure, j'expose le modèle de halo et propose une méthode diagrammatique pour calculer les polyspectres du champ de densité des galaxies et avoir une représentation simple et puissante des termes impliqués. Puis je décris les avant-plans au FDC, tant galactiques que extragalactiques. J'expose la physique de l'effet tSZ et comment décrire sa distribution spatiale avec le modèle de halo. Puis je décris les sources extragalactiques et présente une prescription pour la NG de sources corrélées. Pour le fond diffus infrarouge (FDI) j'introduis une modélisation physique par le modèle de halo et la méthode diagrammatique. Je calcule numériquement le bispectre 3D des galaxies et obtiens la première prédiction du bispectre angulaire FDI. Je montre les différentes contributions et l'évolution temporelle du bispectre des galaxies. Pour le bispectre du FDI, je montre ses différents termes, sa dépendence en échelle et en configuration, et comment il varie avec les paramètres du modèle. Par analyse de Fisher, je montre qu'il apporte de fortes contraintes sur ces paramètres, complémentaires ou supérieures à celles venant du spectre. Enfin, je décris mon travail de mesure de la NG. J'introduis d'abord un estimateur pour l'amplitude du bispectre FDI, et montre comment le combiner avec de similaires pour les sources radio et le FDC, pour une contrainte jointe des différentes sources de NG. Je quantifie la contamination des sources ponctuelles à l'estimation de NG primordiale ; pour Planck elle est négligeable aux fréquences centrales du FDC. Je décris ensuite ma mesure du bispectre FDI sur les données Planck ; il est détecté très significativement à 217, 353 et 545 GHz, avec des SNR allant de 5.8 à 28.7. Sa forme est cohérente entre les différentes fréquences, de même que l'amplitude intrinsèque de NG. Enfin, je décris ma mesure du bispectre tSZ, sur des simulations et sur les cartes tSZ estimées par Planck, validant la robustesse de l'estimation via des simulations d'avant-plans. Le bispectre tSZ est détecté avec un SNR~200. Son amplitude et sa dépendence en échelle et en configuration sont cohérentes avec la carte des amas détectés et avec les simulations. Enfin, cette mesure place une contrainte sur les paramètres cosmologiques : sigma_8 (Omega_b/0.049)^0.35 = 0.74+/-0.04 en accord avec les autres statistiques tSZ. / This PhD thesis, written in english, studies the non-Gaussianity (NG) of extragalactic foregrounds to the Cosmic Microwave Background (CMB), the latter being one of the golden observables of today's cosmology. In the last decade has emerged research for deviations of the CMB to the Gaussian law, as they would discriminate the models for the generation of primordial perturbations. However the CMB measurements, e.g. by the Planck satellite, are contaminated by several foregrounds. I studied in particular the extragalactic foregrounds which trace the large scale structure of the universe : radio and infrared point-sources and the thermal Sunyaev-Zel'dovich effect (tSZ). I hence describe the statistical tools to characterise a random field : the correlation functions, and their harmonic counterpart : the polyspectra. In particular the bispectrum is the lowest order indicator of NG, with the highest potential signal to noise ratio (SNR). I describe how it can be estimated on data, accounting for a potential mask (e.g. galactic), and propose a method to visualise the bispectrum, which is more adapted than the already existing ones. I then describe the covariance of a polyspectrum measurement, a method to generate non-Gaussian simulations, and how the statistic of a 3D field projects onto the sphere when integrating along the line-of-sight. I then describe the generation of density perturbations by the standard inflation model and their possible NG, how they yield the CMB anisotropies and grow to form the large scale structure of today's universe. To describe this large scale structure, I present the halo model and propose a diagrammatic method to compute the polyspectra of the galaxy density field and to have a simple and powerful representation of the involved terms. I then describe the foregrounds to the CMB, galactic as well as extragalactic. I briefly describe the physics of the thermal Sunyaev-Zel'dovich effect and how to describe its spatial distribution with the halo model. I then describe the extragalactic point-sources and present a prescription for the NG of clustered sources. For the Cosmic Infrared Background (CIB) I introduce a physical modeling with the halo model and the diagrammatic method. I compute numerically the 3D galaxy bispectrum and produce the first theoretical prediction of the CIB angular bispectrum. I show the contributions of the different terms and the temporal evolution of the galaxy bispectrum. For the CIB angular bispectrum, I show its different terms, its scale and configuration dependence, and how it varies with model parameters. By Fisher analysis, I show it allows very good constraints on these parameters, complementary to or better than those coming from the power spectrum. Finally, I describe my work on measuring NG. I first introduce an estimator for the amplitude of the CIB bispectrum, and show how to combine it with similar ones for radio sources and the CMB, for a joint constraint of the different sources of NG. I quantify the contamination of extragalactic point-sources to the estimation of primordial NG ; for Planck it is negligible for the central CMB frequencies. I then describe my measurement of the CIB bispectrum on Planck data ; it is very significantly detected at 217, 353 and 545 GHz with SNR ranging from 5.8 to 28.7. Its shape is consistent between frequencies, as well as the intrinsic amplitude of NG. Ultimately, I describe my measurement of the tSZ bispectrum, on simulations and on Compton parameter maps estimated by Planck, validating the robustness of the estimation thanks to realist foreground simulations. The tSZ bispectrum is very significantly detected with SNR~200. Its amplitude and its scale and configuration dependence are consistent with the projected map of detected clusters and tSZ simulations. Finally, this measurement allows to put a constraint on the cosmological parameters : sigma_8*(Omega_b/0.049)^0.35 = 0.74+/-0.04 in agreement with other tSZ statistics.

<p>This dissertation is concerned with two of the largest questions that we can ask about the nature of physical reality: first, whether physical reality begin to exist and, second, what criteria would physical reality have to fulfill in order to have had a beginning? Philosophers of religion and theologians have previously addressed whether physical reality began to exist in the context of defending the Kal{\'a}m Cosmological Argument (KCA) for theism, that is, (P1) everything that begins to exist has a cause for its beginning to exist, (P2) physical reality began to exist, and, therefore, (C) physical reality has a cause for its beginning to exist. While the KCA has traditionally been used to argue for God's existence, the KCA does not mention God, has been rejected by historically significant Christian theologians such as Thomas Aquinas, and raises perennial philosophical questions -- about the nature and history of physical reality, the nature of time, the nature of causation, and so on -- that should be of interest to all philosophers and, perhaps, all humans. While I am not a religious person, I am interested in the questions raised by the KCA. In this dissertation, I articulate three necessary conditions that physical reality would need to fulfill in order to have had a beginning and argue that, given the current state of philosophical and scientific inquiry, we cannot determine whether physical reality began to exist.</p>