abstract: In the past three decades with the deployment of space-based from x-rays to infrared telescopes and operation of 8-10 m class ground based telescopes, a hand-full of regions of the sky have emerged that probe the distant universe over relatively wide fields with the aim of understanding the assembly of apparently faint galaxies. To explore this new frontier, observations were made with the Large Binocular Cameras (LBCs) on the Large Binocular Telescope (LBT) of a well-studied deep field, GOODS-North, which has been observed by a wide range of telescopes from the radio to x-ray. I present a study of the trade-off between depth and resolution using a large number of LBT/LBC U-band and R-band imaging observations in the GOODS-N field. Having acquired over 30 hours of data (315 images with 5-6 minute exposures) for U-band and 27 hours for R-band (828 images with 2 minute exposures), multiple mosaics were generated, starting with images taken under the best atmospheric conditions (FWHM <0.8"). For subsequent mosaics, data with coarser seeing values were added in until the final, deepest mosaic included all images with FWHM <1.8". For each mosaic, object catalogs were made to compare the optimal-resolution, yet shallower image to the low-resolution but deeper image. For the brightest galaxies within the GOODS-N field, structure and clumpy features within the galaxies are more prominent in the optimal-resolution image compared to the deeper mosaics. I conclude that for studies of brighter galaxies and features within them, the optimal-resolution image should be used. However, to fully explore and understand the faintest objects, the deeper imaging with lower resolution are also required. For the 220 and 360 brightest galaxies in the U-band and R-band images respectively, there is only a marginal difference between the optimal-resolution and lower-resolution light-profiles and their integrated total fluxes. This helps constrain how much flux can be missed in galaxy outskirts, which is important for studies of Extragalactic Background Light. Finally, I also comment on a collection of galaxies in the field with tidal tails and streams, diffuse plumes, and bridges. / Dissertation/Thesis / Doctoral Dissertation Astrophysics and Astronomy 2018

The need to accurately measure multi-junction (MJ) tandem solar cells' subcell current-voltage characteristics is increasing due to the vital information they provide about the efficiency, stability, and longevity of the cells. These measurements are rather difficult compared to their counterpart single-layer solar cell measurements. The purpose of this project is to construct an instrument that is able to successfully bias multiple subcells in a tandem solar cell. This would allow accurate measurements of the J-V behaviours of individual subcells within the stack and by extent, allow analysis to optimise future tandem cell technology. The instrument made is a controllable multi-chromatic light-emitting diode array, consisting of six wavelength-different LEDs ranging between ultraviolet and infrared light, which the intensity of is controlled bya slider control Graphical User Interface (GUI). This instrument will bemounted on a laboratory station at the institution of solar cell technology, Ångström laboratory. Although not perfect, the instrumentcan provide sufficient background light for biasing subcells of an MJ solar cell for a wide selection of cell band gaps

La propagation des rayons Ɣ de très haute énergie (E > 100GeV) dans l'univers est affectée par les propriétés du milieu extragalactique. Ces photons à l'échelle du TeV, issus des processus d'accélération de particules dans les noyaux actifs de galaxies, peuvent en effet interagir avec des photons du fond optique et infrarouge qui baignent l'univers et produire des paires d'électrons et de positrons. Ce processus réduit la transparence de l'univers aux rayons Ɣ de très haute énergie mais permet en revanche de sonder les propriétés du milieu extragalactique de façon unique. Dans cette thèse, les données prises par le réseau de télescopes à imagerie Tcherenkov atmosphérique H.E.S.S. sont analysées et utilisées afin de caractériser la transparence de l'univers aux rayons Ɣ de très haute énergie. Une mesure indépendante de la distribution spectrale en énergie du fond cosmologique optique et infrarouge est réalisée à travers l'ajustement des modulations observées dans les spectres en énergie obtenus avec H.E.S.S. pour un échantillon de noyaux actifs de galaxies brillants dans une gamme en redshift 0.03 < z < 0.28. Les résultats obtenus sont compatibles avec les limites inférieures dérivées par comptages de galaxies et ne suggèrent pas d'anomalie de la transparence de l'univers aux rayons Ɣ vis à vis des modèles actuels du fond de lumière extragalactique. Des processus de second ordre affectant la propagation des rayons Ɣ de très haute énergie sont également explorés. Des limites sur une brisure de la symétrie de Lorentz à l'échelle de Planck sont obtenues à partir de l'analyse spectrale du noyau actif Mrk 501 observé dans un état de flux exceptionnel par H.E.S.S. en 2014, à grand angle zénithal. Enfin, des contraintes sur le champ magnétique extragalactique sont dérivées en considérant l'émission Ɣ secondaire attendue à partir de simulations des cascades électromagnétiques initiées lors du processus d'absorption pour le noyau actif distant PG 1553+113 vu par H.E.S.S. et le télescope spatial Fermi. Cette thèse a également été l'occasion d'une participation aux développements de certains aspects de la calibration et de l'analyse des données de H.E.S.S. / The propagation of very high energy Ɣ rays in the universe depends on the properties of the extragalactic medium. Such TeV-scale photons travelling cosmological distances are -emitted through particle acceleration mechanisms in active galaxy nuclei- can interact with the low-energy photons of the extragalactic background light (EBL) and produce electron-positron pairs. This effect reduces the transparency of the universe to very high energy Ɣ rays but it also provides a unique opportunity to probe the properties of the extragalactic medium. In this thesis, data taken with the H.E.S.S. array of Cherenkov telescopes are analyzed and used to characterize the transparency of the universe to very high energy Ɣ rays. A independent measurement of the spectral energy distribution of the EBL with H.E.S.S. is presented. It is obtained by extracting the EBL absorption signal from the fit of spectral modulations in the high-quality spectra of a sample of bright blazars in the redshift range 0.03 < z < 0.28. The intensity of the EBL obtained in different spectral bands is presented together with the associated Ɣ-ray horizon. The obtained results are consistent with lower limits derived from galaxy counts and do not suggest an anomaly of the transparency of the universe to Ɣ rays with respect to current models of the extragalactic background light. Second-order processes affecting the propagation of very high energy Ɣ rays in the universe are also considered. Limits on Lorentz invariance violation at Planck scale are obtained from the spectral analysis of the active galaxy nucleus Mrk 501 observed during a high-flux state by H.E.S.S. in 2014, at large zenith angle. Finally, constraints on the extragalactic magnetic field properties are derived by considering the secondary Ɣ-ray emission expected from the simulation of electromagnetic cascades initiated by the absorption process for the distant active galaxy nucleus PG 1553+113 seen by H.E.S.S. and the Fermi Ɣ-ray space telescope. In this thesis some developments related to the calibration and analysis of H.E.S.S. data are also presented.

Axionartige Teilchen sind pseudoscalare Teilchen welche in Theorien jenseits des Standardmodells vorhergesagt werden. Falls ein axionartiges Teilchen innerhalb eines kosmischen magnetischen Felds gebildet wird, wird dieses nicht durch das Hintergrundlicht absorbiert. Daher kann es kosmische Distanzen überbrücken bevor es wieder in ein Photon zurück oszilliert. Dieser Effekt erhöht die Reichweite der Gammastrahlung im Universum. Im Rahmen dieser Dissertation werden Daten des Fermi Large Area Telescopes, aufgenommen über eine Zeitraum von sechs Jahren, systematisch analysiert. Hierbei wird nach axionartigen Teilchen mit Hilfe von Transparenzeffekten des Universums gesucht. In diesem Zusammenhang werden verschiedene Modelle des extragalaktischen Hintergrundlichts mit und ohne Berücksichtigung axionartiger Teilchen verglichen. Hierfür werden Likelihood-Funktionen für das höchst energetische Photon verschiedener entfernter Quelle kombiniert. Diese sind aktive galaktische Kerne mit einer Rotverschiebung z ≥0.1 des Second Catalog of Hard Fermi-LAT Sources. Unter den Annahmen einer intergalaktischen magnetischen Feldstärke von B = 1 nG und einer Kohärenzlänge von s = 1 Mpc wurde keine Veränderungen der Transparenz durch axionähnliche Teilchen nachgewiesen. Für eine Masse eines axionartigen Teilchens mit m≅ 3.0 neV wird eine Photonen-Axion Kopplungskonstante über 10(^11) GeV(^−1) ausgeschlossen. / Axion-like particles, pseudo-scalar particles that arise in theories beyond the Standard Model, mix with photons in the presence of magnetic fields. If an axion-like particle is produced within a cosmic magnetic field, it evades extragalactic background light absorption and thus it can survive cosmological distances until oscillating back into a photon. This leads to an increased transparency of the Universe to gamma rays. In the scope of this thesis, we search for transparency effects compatible with the existence of axion-like particles with six years of data from the Fermi Large Area Telescope. We derive and combine the likelihoods of the highest-energy photon events from a sample of hard distant sources, in order to compare models that include axion-like particles and models with only extragalactic background light. The sources are active galactic nuclei from the Second Catalog of Hard Fermi sources at redshift z≥0.1. For values of the intergalactic magnetic field strength B = 1 nG and coherence length s = 1 Mpc, we find no evidence for a modified transparency induced by axion-like particles and therefore we set upper limits. We exclude photon-axion coupling constants above 10(^11) GeV(^−1) for axion masses m≅ 3.0 neV.

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