Fakultät für Physik - Digitale Hochschulschriften der LMU - Teil 04/05

In dieser Arbeit untersuche ich den Einfluss massiver Quantenfelder auf einen reinen de Sitter Hintergrund. Nach einer kurzen Zusammenfassung der neuesten Entwicklungen zu diesem Thema gebe ich eine Einführung in die klassische Geometrie von de Sitter Räumen. Darin behandle ich die physikalischen Eigenschaften und die verschiedenen Koordinatensysteme, die unterschiedliche Teile des de Sitter Raumes bedecken. Im anschließenden Kapitel wiederhole ich die Quantenfeldtheorie freier Skalarfelder auf gekrümmten Hintergründen im Allgemeinen und auf de Sitter im Speziellen. Hier gebe ich die Lösungen für die Modenfunktionen in geschlossenen und flachen Koordinaten an und diskutiere das Problem der richtigen Wahl des Vakuums auch im Hinblick auf die Eigenschaften der zugehörigen Green Funktionen. Da sich der Hintergrund für die Quantenfeldtheorie auf de Sitter mit der Zeitentwicklung ändert, verwende ich den in/in (Keldysh) Formalismus zur Berechnung von Observablen. Ich fasse den Formalismus zusammen und erläutere die für Rechnungen benötigten Methoden. Die Einführung des Wechselwirkungspotentials und der Feynmanregeln für Wechselwirkungsdiagramme bilden schliesslich den Abschluss des einleitenden Teils. Mit Hilfe des effektiven Potentials für das reskalierte Skalarfeld zeige ich, dass jede Theorie mit ungeraden Wechselwirkungspotentialen Probleme mit der Stabilität des freien Vakuums aufweist, falls der Skalenfaktor in der Vergangenheit verschwindet. Dies ist auch ein Argument, auf de Sitter die globalen Koordinaten anstelle der flachen zu verwenden, da sie im Gegensatz zu diesen den ganzen Raum bedecken und der Skalenfaktor nur einen nicht verschwindenden Minimalwert annimmt. Ich beweise weiterhin, dass aus der Betrachtung der Vakuumpersistenz kein Einwand gegen Wechselwirkungen auf de Sitter folgt, da die resultierende Entwicklung immer unitär ist, falls die Kopplung klein genug gewählt wird. Für die Schleifenkorrekturen zum Keldyshpropagator in globalen Koordinaten ergeben meine Berechnungen keine problematischen Divergenzen. Insbesondere finde ich keine Divergenz, die es verbietet, den adiabatischen Limes in Berechnung zu nehmen, was den Ergebnissen von Polyakov und Krotov widerspricht. Zusammen- fassend ist meine Schlussfolgerung, dass die wechselwirkenden Quantenfelder zu keinen offensichtlichen Instabilitäten des de Sitter Hintergrundes führen.

This modelling study aims to gain an improved understanding of the processes that determine the water vapour budget in the stratosphere by means of the investigation of water isotope ratios. At first, a separate hydrological cycle has been introduced into the chemistry-climate model EMAC, including the water isotopologues HDO and H218O and their physical fractionation processes. Additionally, an explicit computation of the contribution of methane oxidation to HDO has been incorporated. EMAC simulates explicit stratospheric dynamics and a highly resolved tropical tropopause layer. These model expansions, now allow detailed analyses of water vapour and its isotope ratio with respect to deuterium (deltaD(H2O)), throughout the stratosphere and in the transition region to the troposphere. In order to assure the correct representation of the water isotopologues in the model's hydrological cycle, the expanded system has been evaluated in several steps. The physical fractionation effects have been evaluated by comparison of the simulated isotopic composition of precipitation with measurements from a ground-based network (GNIP) and with the results from an isotopologue-enabled ECHAM5 general circulation model version. The model's representation of the chemical HDO precursor CH3D in the stratosphere has been confirmed by a comparison with chemical transport models (CHEM1D, CHEM2D) and measurements from radiosonde flights. Finally, the simulated HDO and deltaD(H2O) have been evaluated in the stratosphere, with respect to retrievals from three different satellite instruments (MIPAS, ACE-FTS, SMR). Discrepancies in stratospheric deltaD(H2O) between two of the three satellite retrievals can now partly be explained. The simulated seasonal cycle of tropical deltaD(H2O) in the stratosphere exhibits a weak tape recorder signal, which fades out at altitudes around 25 km. This result ranges between the pronounced tape recorder signal in the MIPAS observations and the missing upward propagation of the seasonal variations in the ACE-FTS retrieval. Revisions of different insufficencies in the respective satellite measurements, however, are expected to alter both observational datasets towards the results of the EMAC model. Extensive analyses of the water isotope ratios have revealed the driving mechanisms of the stratospheric deltaD(H2O) tape recorder signal in the EMAC simulation. A sensitivity study without the impact of methane oxidation on deltaD(H2O) demonstrates the damping effect of this chemical process on the tape recorder signal. An investigation of the origin of the enhanced deltaD(H2O) in the lower stratosphere during boreal summer, shows isotopically enriched water vapour, crossing the tropopause over the subtropical Western Pacic. A correlation analysis confirms this link, and thus the Asian Summer Monsoon could be identified to be the major contributing process for the stratospheric deltaD(H2O) tape recorder. This finding contradicts an analysis of ACE-FTS satellite data, which assigns the lower stratospheric deltaD(H2O) increase during boreal summer to the North American Monsoon. A possible explanation for this discrepancy has been found to be an underrepresentation of convective ice overshooting in the applied convection scheme.

Wed, 28 May 2014 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/17034/ https://edoc.ub.uni-muenchen.de/17034/1/Schreiber_Robert.pdf Schreiber, Robert ddc:530, ddc:500, Fakultät für Physik

Der Beitrag der Luftfahrt am gesamten anthropogenen Strahlungsantrieb beträgt 3-8 %. Mit steigendem Luftverkehrsaufkommen um etwa 5 % jährlich wächst dieser Beitrag stetig an. Kondensstreifenzirren machen den größten Anteil an der Klimawirkung des Luftverkehrs aus. Die Ergebnisse der bisherigen Studien sind aber noch mit großen Unsicherheiten versehen. Mit dem Ziel einer realistischeren Darstellung von Kondensstreifenzirren und genaueren Validierungsmöglichkeiten der Kondensstreifenzirren-Parametrisierung im Klimamodell wird in dieser Arbeit die Parametrisierung der mikrophysikalischen und optischen Eigenschaften von Kondensstreifenzirren, welche einen großen Einfluss auf deren Klimawirksamkeit haben, verbessert. Als Vorarbeit musste das im Klimamodell ECHAM5 verwendete Zwei-Momenten-Schema für natürliche Wolken in Bezug auf die Konsistenz der Mikrophysik mit einem fraktionellen Bedeckungsgradschema modifiziert werden. Zudem wurde die Nukleationsparametrisierung um den Einfluss durch präexistierendes Eis erweitert. Die für ECHAM4 entwickelte Kondensstreifenzirren-Parametrisierung wurde in ECHAM5 übertragen und um das Zwei- Momenten-Schema erweitert. Neben dem Eiswassergehalt wird damit auch die Eispartikelanzahldichte im Modell prognostiziert. Folglich kann die mittlere Eispartikelgröße bestimmt werden. Es stellte sich heraus, dass genaue Informationen über die Ausdehnung des Volumens der Kondensstreifenzirren wichtig für die Darstellung der mikrophysikalischen und optischen Eigenschaften der Kondensstreifenzirren sind. Der Einfluss von Diffusion und Sedimentation auf die Vergrößerung des Volumens der Kondensstreifenzirren wurde im Modell parametrisiert. Das Ergebnis zeigt eine ähnliche globale Verteilung der Kondensstreifenzirren wie in der Studie mit ECHAM4. Die Bedeckungsgrade sind jedoch höher, zeigen aber im Vergleich mit Satellitendaten gute Übereinstimmungen. Die optische Dicke orientiert sich einerseits an der Höhe des Eiswassergehalts. Beide zeigen Maxima in den Tropen, wo die Menge des kondensierbaren Wasserdampfs hoch ist. Andererseits orientiert sich die globale Verteilung der mikrophysikalischen und optischen Eigenschaften, anders als in früheren Studien, stark an der Flugverkehrsdichte. Durch häufige Bildung von Eispartikeln in den Hauptfluggebieten bleibt die Eispartikelanzahldichte groß und die mittlere Partikelgröße klein. Folglich ist die optische Dicke in diesen Gebieten durch die Berücksichtigung der Eispartikelanzahldichte höher als in früheren Studien. Wenn man, wie in früheren Studien, das Strahlungschema mit einer Beschränkung auf größere Eispartikel anwendet, ist der Strahlungsantrieb mit 29 mW/m2 im Vergleich zur vorangegangenen Studie in ECHAM4 etwas geringer. Emittierte Rußpartikel aus den Flugzeugtriebwerken stellen eine dominierende Quelle der Eispartikel in Kondensstreifenzirren dar. Die erweiterte Parametrisierung von Kondensstreifenzirren im Modell ist Voraussetzung für eine Studie über den Einfluss einer Rußemissionsänderung auf den Strahlungsantrieb von Kondensstreifenzirren. Bei einer angenommenen Reduzierung der initialen Eispartikelanzahldichte um 80 % werden die Eispartikel größer und die optische Dicke kleiner. Der Bedeckungsgrad der sichtbaren Kondensstreifenzirren veringert sich um mehr als die Hälfte, jedoch wurde die Vermutung, dass sich die Lebensdauer der Kondensstreifenzirren durch die Bildung größerer Eispartikel verkürzt, nicht bestätigt.

In kühlen Sternen wie der Sonne wird die nuklear erzeugte Energie aus dem Inneren an die Oberfläche transportiert. Diese kann dann in den freien Weltraum entfliehen, und so können wir das Sternenlicht letztlich beobachten. Die theoretische Modellierung des photosphärischen Übergangsbereiches – vom konvektiven zum radiativen Energietransport – ist aufgrund der inhärenten dreidimensionalen (3D) Natur der Konvektion und der komplexen, nicht-linearen und nicht-lokalen Interaktionen des Strahlungsfelds mit dem stellaren Plasma sehr anspruchsvoll. Theoretische Atmosphärenmodelle stellen die fundamentale Basis für die Untersuchung von Sternen dar, daher sind Astronomen für ihr Verständnis der Sterne auf diese letztlich angewiesen. Die üblicherweise verwendeten eindimensionalen (1D) Atmosphärenmodelle beinhalten verschiedene Vereinfachungen. Insbesondere wird die Konvektion für gewöhnlich mit der Mischungswegtheorie berechnet, trotz ihrer wohlbekannten Fehler, da derzeit keine deutlich besseren Alternativen vorhanden sind. Der einzige Ausweg, um dieses Problem zu überwinden ist, die zeitabhängigen, dreidimensionalen, hydrodynamischen Gleichungen, welche mit einem realistischen Strahlungstransport gekoppelt sind, zu lösen. Aufgrund der in den vergangenen Jahrzehnten rasch gestiegenen Rechenleistung wurden bedeutende Fortschritte mit Simulationen für 3D Strahlungshydrodynamik (RHD) von Atmosphären erzielt. Diese Modelle sind außerordentlich leistungsfähig, und besitzen eine enorme Vorhersagekraft, wie präzise Vergleiche mit Sonnenbeobachtungen wiederholt beweisen konnten. Ausgestattet mit diesen ausgereiften Methoden möchte ich als Ziel meiner Dissertation die drei folgenden Fragen näher untersuchen: Was sind die Eigenschaften der Atmosphären von kühlen Sternen? Welche Unterschiede sind zwischen den 1D und 3D Modellen vorhanden? Wie verändern sich die Vorhersagen für die Sternstrukturen und Spektrallinien? Um mich dieser Aufgabenstellung systematisch anzunehmen, habe ich das Stagger-Gitter berechnet. Das Stagger-Gitter ist ein umfangreiches Gitter aus 3D RHD Atmosphärenmodellen von kühlen Sternen, welches einen großen stellaren Parameterbereich abdeckt. In der vorliegenden Dissertation beschreibe ich die Methoden, welche angewendet wurden, um die vielen Atmosphärenmodelle zu berechnen. Zudem werden die allgemeinen Eigenschaften der resultierenden 3D Modelle, auch deren zeitliche und räumliche Mittelwerte detailliert dargestellt und diskutiert. Die Unterschiede zwischen den 1D und 3D Schichtungen, sowie die Details der stellaren Granulation (die Manifestation der Konvektion unterhalb der Sternoberfläche) werden ebenfalls umfangreich erläutert und beschrieben. Des Weiteren habe ich folgende Anwendungen für die 3D Atmosphärenmodelle untersucht: Berechnung theoretischer Spektrallinien, wichtig für die Bestimmung von Sternparametern, Spektroskopie und Häufigkeiten-Analyse; die sogenannte Randverdunkelung, notwendig für die Analyse interferometrischer Beobachtungen und Suche nach extrasolaren Planeten; und die Kalibrierung der Mischungsweglänge, womit 1D-Sternmodelle verbessert werden können. Die Qualität der hochauflösenden Beobachtungen hat inzwischen die der theoretischen 1D Atmosphärenmodelle aufgrund der technischen Entwicklungen in den vergangenen Jahren überschritten. Daher hat sich der Bedarf an besseren Simulationen für Atmosphärenmodelle erhöht. Durch die Bereitstellung eines umfangreichen Gitters aus 3D RHD Atmosphärenmodellen wurde dazu ein erheblicher Beitrag geleistet. Damit werden wir den Anforderungen an die Theorie für die derzeitigen und zukünftigen Beobachtungen gerecht werden, und können somit zu einem besseren Verständnis der kühlen Sterne beitragen.

Fri, 9 May 2014 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/17138/ https://edoc.ub.uni-muenchen.de/17138/1/Do_Jaekwon.pdf Do, Jaekwon ddc:530, ddc:500

The chemical compositions of the stars and gas in galaxies play a significant role in all their key evolutionary processes, from gas cooling, through star formation, to the production of new heavy elements that are released back into the gas as stars die in supernova explosions. A theoretical explanation of the production of elements heavier than helium (known simply as `metals' in astrophysics) in stars and its distribution throughout galaxies has been developing since the first postulation of stellar nucleosynthesis in the 1920s. However, there are still a number of unanswered questions in the field of galactic chemical evolution (GCE). For example, what is the most accurate way to measure the metallicities in galaxies? What are the relative contributions to GCE from different types of stars? How is this metal-rich material circulated throughout the various components of a galaxy? And how can we explain the seemingly incompatible chemical properties observed in different galaxies in the local Universe? This thesis provides an investigation into the chemical enrichment of galaxies, by utilising both observations of nearby galaxies and sophisticated GCE models within a semi-analytic model of galaxy evolution. Its core aims are a) to better quantify the chemical properties seen in low-redshift galaxies and explain there likely causes, and b) to develop an improved GCE model that can simultaneously reproduce the diverse chemical properties seen in different types of galaxies in the local Universe. With these aims in mind, Chapter 1 outlines the key background knowledge required for such an investigation. It discusses the different methods used for measuring the metallicity of real galaxies, and their various shortcomings. It also describes simple, analytic GCE models, and the sophisticated semi-analytic model, L-Galaxies, that is used to simulate galaxy evolution in detail. In Chapters 2 and 3, I provide an investigation into the relation between stellar mass (M*), star formation rate (SFR), and gas-phase metallicity (Zg) in galaxies. It is shown that the L-Galaxies model reproduces the positive correlation between SFR and Zg in massive galaxies that is seen when using sophisticated, theoretical metallicity diagnostics. This lends support to the use of such diagnostics over simpler, emission-line ratios. It is further shown that, in the semi-analytic model, this SFR-Zg correlation is due to the gradual dilution of the gas in low-SFR, elliptical galaxies, after a gas-rich merger event. A number of signatures of this particular evolution can be seen in these model galaxies at redshift zero, including low gas fractions and low values of (Zg-Z*). Crucially, all of these properties are also seen in nearby elliptical galaxies in the Sloan Digital Sky Survey (SDSS), providing indirect evidence that such an evolutionary process is also occurring in the elliptical galaxy population in the real Universe. In Chapter 4, I present a new, sophisticated GCE model implemented into L-Galaxies, that significantly improves on the previous scheme. It does this by accounting for the delayed enrichment of many chemical elements from stars, of various initial masses and metallicities, via stellar winds and supernovae. This new scheme enables a much more detailed study of the chemical evolution of galaxies, and enables a comparison with a larger range of observational data. In Chapter 5, I demonstrate that this new model is able to simultaneously reproduce the chemical properties observed in a) the gas of local, star-forming galaxies, b) the photospheres of G dwarfs in the Milky Way disc, and c) the integrated stellar populations of nearby elliptical galaxies. Furthermore, the model is able to do this without any significant deviation from the standard framework of galaxy formation in the canonical paradigm of hierarchical structure formation. This can be seen as a significant achievement, which has allowed us to form a much more comprehensive view of GCE than was possible before.

Die Untersuchung der Moduli Räumen von N = (2,2) Superkonformen Feldtheorien und der allgemeineren N = (2,2) Supersymmetrischen Quanten Feldtheorien ist ein langjähriges und vielseitiges Forschungsgebiet. Diese Dissertation konzentriert sich auf gewisse allgemeine Aspekte des erwähnten Studiums, und stellt Entwicklungen von allgemeinen Methoden im Rahmen der Topologischen String Theorie dar. Die vorliegende Arbeit besteht aus zwei Teilen. Der erste Teil befasst sich mit Aspekten der geschlossenen Topologischen String Theorie und kulminiert in den Inhalt von [52], wo die geometrische Struktur der Topologischen anti-Topologischen Moduli Räumen von N = (2, 2) Superkonformen Feldtheorien mit Zentral Ladung c = 9, angesichts eines allgemeinen Quantisieung-Rahmens [31, 32] wiederentdeckt wird. Aus dieser Sichtweise erhält man, als Spezialfall, eine klare Einsicht der “holomorphic anomaly equation” von [6]. Diese Arbeit könnte als eine natürliche Erweiterung von früheren Untersuchungen in ähnlicher Richtung betrachtet werden, insbesondere vom grundlegenden Artikel [104]. Der zweite Teil befasst sich mit Aspekten der Untersuchung der Offenen und Geschlossenen Moduli Räumen von Topologischen Konformen Feldtheorien auf Genus Null. Insbesondere, ist hier eine Exposition von [13] enthalten, wo allgemeine Resultate über die Klassifizierung und Berechnung von “bulk-induced” Deformationen von Offenen Topologischen Konformen Feldtheorien erhalten wurden. Letzteres wurde durch eine kohärente algebraische Methode erreicht was sich auf den definierenden L∞ und A∞ beteiligten Strukturen bezieht. Teilweise ist die letztere Untersuchung auf beliebige Affine B-twisted Landau Ginzburg Modelle beschränkt. Nachfolgend wird weitere originelle Arbeit dargestellt was die Topologische String-Feld-Theoretische Struktur von B-twisted Landau Ginzburg Modellen vollendet. Insbesondere wird eine “off-shell” Erweiterung der Kapustin-Li Formel von [41, 49] gegeben. Diese “off-shell” Formel bezeichnet einen konsolidierenden Baustein der algebraischen Herangehensweise zur Berechnung des Effektiven Superpotentials von B-twisted Affine Landau Ginzburg Modellen, und kann damit als eine natürliche Entwicklung von der grundlegenden Arbeit [12] betrachtet werden.

Micromegas are high-rate capable, high-resolution micro-pattern gaseous detectors. Square meter sized resistive strip Micromegas are foreseen as replacement of the currently used precision tracking detectors in the Small Wheel, which is part of the forward region of the ATLAS muon spectrometer. The replacement is necessary to ensure tracking and triggering performance of the muon spectrometer after the luminosity increase of the Large Hadron Collider beyond its design value of $10^{34}$,cm$^{-2}$s$^{-1}$ around 2020. In this thesis a novel discharge tolerant floating strip Micromegas detector is presented and described. By individually powering copper anode strips, the effects of a discharge are confined to a small region of the detector. This reduces the impact of discharges on the efficiency by three orders of magnitude, compared to a standard Micromegas. The physics of the detector is studied and discussed in detail. Several detectors are developed: A $6.4times6.4,$cm$^2$ floating strip Micromegas with exchangeable SMD capacitors and resistors allows for an optimization of the floating strip principle. The discharge behavior is investigated on this device in depth. The microscopic structure of discharges is quantitatively explained by a detailed detector simulation. A $48times50,$cm$^2$ floating strip Micromegas is studied in high energy pion beams. Its homogeneity with respect to pulse height, efficiency and spatial resolution is investigated. The good performance in high-rate background environments is demonstrated in cosmic muon tracking measurements with a $6.4times6.4,$cm$^2$ floating strip Micromegas under lateral irradiation with 550,kHz 20,MeV proton beams. A floating strip Micromegas doublet with low material budget is developed for ion tracking without limitations from multiple scattering in imaging applications during medical ion therapy. Highly efficient tracking of 20,MeV protons at particle rates of 550,kHz is possible. The reconstruction of the track inclination in a single detector plane is studied and optimized. A quantitative description of the systematic deviations of the method is developed, that allows for correcting the reconstructed track inclinations. The low material budget detector is tested in therapeutic proton and carbon ion beams at particle rates between 2,MHz and 2,GHz. No reduction of the detector up-time due to discharges is observed. The measurable pulse height decreases by only 20% for an increase of particle rate from 2,MHz to 80,MHz. Efficient single particle tracking is possible at flux densities up to 7,MHz/cm$^2$. The good multi-hit resolution of floating strip Micromegas is shown.

Mon, 28 Apr 2014 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/17315/ https://edoc.ub.uni-muenchen.de/17315/1/Laporte_Chervin_F_P.pdf Laporte, Chervin F. P. ddc:530, ddc:500, Fakultät für Physik

Germanium detectors are a choice technology in fundamental research. They are suitable for the search for rare events due to their high sensitivity and excellent energy resolution. As an example, the GERDA (GERmanium Detector Array) experiment searching for neutrinoless double beta decay is described. The observation of this decay would resolve the fundamental question whether the neutrino is its own antiparticle. Especially adapted detector technologies and low background rates needed to detect very rare events such as neutrinoless double beta decays are discussed. The identification of backgrounds originating from the interaction of radiation, especially alpha-particles, is a focus of this thesis. Low background experiments face problems from alpha-particles due to unavoidable surface contaminations of the germanium detectors. The segmentation of detectors is used to obtain information about the special characteristics of selected events. The high precision test stand GALATEA was especially designed for surface scans of germanium detectors. As part of this work, GALATEA was completed and commissioned. The final commissioning required major upgrades of the original design which are described in detail. Collimator studies with two commercial germanium detectors are presented. Different collimation levels for a beta-source were investigated and crystal axis effects were examined. The first scan with an alpha-source of the passivated end-plate of a special 19-fold segmented prototype detector mounted in GALATEA is described. The alpha-induced surface events were studied and characterized. Crosstalk and mirror pulses seen in the segments of the germanium detector were analyzed. The detector studies presented in this thesis will help to further improve the design of germanium detectors for low background experiments.

Fri, 11 Apr 2014 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/16901/ https://edoc.ub.uni-muenchen.de/16901/1/Rau_Stefan.pdf Rau, Stefan ddc:530, ddc:500, Fakultät für Physik

This thesis unifies several studies, which all are dedicated to the subject of statistical data analysis in radio astronomy and radio astrophysics. Radio astronomy, like astronomy as a whole, has undergone a remarkable development in the past twenty years in introducing new instruments and technologies. New telescopes like the upgraded VLA, LOFAR, or the SKA and its pathfinder missions offer unprecedented sensitivities, previously uncharted frequency domains and unmatched survey capabilities. Many of these have the potential to significantly advance the science of radio astrophysics and cosmology on all scales, from solar and stellar physics, Galactic astrophysics and cosmic magnetic fields, to Galaxy cluster astrophysics and signals from the epoch of reionization. Since then, radio data analysis, calibration and imaging techniques have entered a similar phase of new development to push the boundaries and adapt the field to the new instruments and scientific opportunities. This thesis contributes to these greater developments in two specific subjects, radio interferometric imaging and cosmic magnetic field statistics. Throughout this study, different data analysis techniques are presented and employed in various settings, but all can be summarized under the broad term of statistical infer- ence. This subject encompasses a huge variety of statistical techniques, developed to solve problems in which deductions have to be made from incomplete knowledge, data or measurements. This study focuses especially on Bayesian inference methods that make use of a subjective definition of probabilities, allowing for the expression of probabilities and statistical knowledge prior to an actual measurement. The thesis contains two different sets of application for such techniques. First, situations where a complicated, and generally ill-posed measurement problem can be approached by assuming a statistical signal model prior to infer the desired measured variable. Such a problem very often is met should the measurement device take less data then needed to constrain all degrees of freedom of the problem. The principal case investigated in this thesis is the measurement problem of a radio interferometer, which takes incomplete samples of the Fourier transformed intensity of the radio emission in the sky, such that it is impossible to exactly recover the signal. The new imaging algorithm RESOLVE is presented, optimal for extended radio sources. A first showcase demonstrates the performance of the new technique on real data. Further, a new Bayesian approach to multi-frequency radio interferometric imaging is presented and integrated into RESOLVE. The second field of application are astrophysical problems, in which the inherent stochas- tic nature of a physical process demands a description, where properties of physical quanti- ties can only be statistically estimated. Astrophysical plasmas for instance are very often in a turbulent state, and thus governed by statistical hydrodynamical laws. Two studies are presented that show how properties of turbulent plasma magnetic fields can be inferred from radio observations.

Wed, 9 Apr 2014 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/16871/ https://edoc.ub.uni-muenchen.de/16871/1/Otten_Marcus.pdf Otten, Marcus

Thu, 27 Feb 2014 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/17017/ https://edoc.ub.uni-muenchen.de/17017/1/Orban_de_Xivry_Gilles.pdf Orban de Xivry, Gilles

Two analyses searching for squarks and gluinos which decay into final states with multiple jets, an isolated electron or muon and a large missing transverse energy are presented. Both rely on data taken by the ATLAS detector in pp collisions at a center-of-mass energy of 8 TeV at the LHC during 2012. The first analysis uses a subset of 5.8 fb-1 of this dataset, the other analysis uses the full statistics of 20.3 fb-1. Both analysis share the same methods regarding the triggers and the background estimation techniques. The two dominant backgrounds are ttbar and W+jets production. The ttbar and the W+jets backgrounds are estimated in a semi-data-driven method. The minor QCD multi-jet background is estimated in an entirely data-driven method. The final background estimates in the analyses are derived in a profile-log-likelihood fit. None of the analyses sees an excess beyond Standard Model expectations. The analysis of the partial dataset derives limits in a MSUGRA/CMSSM model with parameters A_0=0, tan(beta) = 10 and mu > 0 and excludes squarks and gluinos with masses below 1.2 TeV for equal squark and gluino masses. The analysis of the full dataset derives limits in simplified models and in a MSUGRA/CMSSM model with parameters A_0=-2 m_0, tan(beta) = 30 and mu > 0. Gluinos (squarks) with masses below 1.2 TeV (750 GeV) can be excluded for vanishing LSP masses in simplified models. Gluino masses below 1.2 TeV can be excluded for every m_0 value in the MSUGRA/CMSSM model.

Wed, 26 Feb 2014 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/16756/ https://edoc.ub.uni-muenchen.de/16756/1/Stephan_Anton.pdf Stephan, Anton ddc:530, ddc:500, Fakultät für Physik

Why do we exist? CP violation is an integral part of this question as its understanding is crucial to explain the matter-antimatter asymmetry observed in our universe. Several experiments were designed and carried out to precisely measure CP violation, especially in the B meson system where large asymmetries where predicted and found. With Belle II and LHCb, two new experiments are going to improve the existing measurements. Belle II will be based on the very successful Belle experiment at the KEKB collider, currently holding the world record on luminosity with 2.11×10³⁴ cm⁻²2s⁻¹. The B meson system has a very rich decay topology and many of theses decay modes and their CP asymmetry parameters have already been measured at Belle. The most famous decay channel, B0⟶J/ψK0s, poses very tight constraints on sin 2φ₁ but leaves a twofold ambiguity on the actual value of the angle φ₁ in the CKM triangle. The decay mode B0⟶D*-D*+K0s, while experimentally much more challenging, offers the unique possibility to also extract cos2φ₁ and thus resolve this ambiguity. In the first chapters of this thesis we present the principle of this measurement and the results for the branching fraction and the time-dependent CP violation parameters of B0⟶D*-D*+K0s decays. These results are obtained from the final data sample of the Belle experiment containing 772 million BBbar pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. We obtain the branching fraction BR(B0⟶D*-D*+K0s) = (5.35+0.35−0.34(stat) ± 0.57(syst))×10⁻³, which is in agreement with the current world average. In a 3 parameter fit sensitive to cos2φ₁, we extract the currently most precise values for the CP parameters Jc/J0 = 0.37 ± 0.10(stat) ± 0.02(syst), (2Js1/J0) sin(2φ₁) = 0.30 ± 0.16(stat) ± 0.03(syst), (2Js2/J0) cos(2φ₁) = 0.16 ± 0.16(stat) ± 0.03(syst). This allows us to exclude a negative value for cos2φ₁ at a 85% confidence under the assumption that that (2Js2/J0) is positive. Finally, we describe the implementation of the vertex detector geometry for the upcoming Belle II experiment. The upgrade to Belle aims to increase the integrated luminosity by a factor of 50 and will receive, among other upgrades, a completely new vertex detector. To produce simulated events, a precise description of the sensor geometry and material budget is needed.

One of the most fundamental correlations between the properties of galaxies in the local Universe is the so-called morphology-density relation (Dressler 1980). A plethora of studies utilizing multi-wavelength tracers of activity have shown that late type star forming galaxies favour low density regions in the local Universe (e.g. G´omez et al. 2003). In particular, the cores of massive galaxy clusters are galaxy graveyards full of massive spheroids that are dominated by old stellar populations. A variety of physical processes might be effective in suppressing star formation and affecting the morphology of cluster and group galaxies. Broadly speaking, these can be grouped in two big families: (i) interactions with other cluster members and/or with the cluster gravitational potential and (ii) interactions with the hot gas that permeates massive galaxy systems. Galaxy groups are the most common galaxy environment in our Universe, bridging the gap between the low density field and the crowded galaxy clusters. Indeed, as many as 50%-70% of galaxies reside in galaxy groups in the nearby Universe (Huchra & Geller 1982; Eke et al. 2004), while only a few percent are contained in the denser cluster cores. In addition, in the current bottom-up paradigm of structure formation, galaxy groups are the building blocks of more massive systems: they merge to form clusters. As structures grow, galaxies join more and more massive systems, spending most of their life in galaxy groups before entering the cluster environment. Thus, it is plausible to ask if group-related processes may drive the observed relations between galaxy properties and their environment. To shed light on this topic we have built the largest X-ray selected samples of galaxy groups with secure spectroscopic identification on the major blank field surveys. For this purpose, we combine deep X-ray Chandra and XMM data of the four major blank fields (All-wavelength Extended Groth Strip International Survey (AEGIS), the COSMOS field, the Extended Chandra Deep Field South (ECDFS), and the Chandra Deep Field North (CDFN) ). The group catalog in each field is created by associating any X-ray extended emission to a galaxy overdensity in the 3D space. This is feasible given the extremely rich spectroscopic coverage of these fields. Our identification method and the dynamical analysis used to identify the galaxy group members and to estimate the group velocity dispersion is extensively tested on the AEGIS field and with mock catalogs extracted from the Millennium Simulation (Springel et al. 2005). The effect of dynamical complexity, substructure, shape of X-ray emission, different radial and redshift cuts have been explored on the LX −sigma relation. We also discover a high redshift group at z~1.54 in the AEGIS field. This detection illustrates that mega-second Chandra exposures are required for detecting such objects in the volume of deep fields. We provide an accurate measure of the Star Formation Rate (SFR) of galaxies by using the deepest available Herschel PACS and Spitzer MIPS data available for the considered fields. We also provide a well-calibrated estimate of the SFR derived by using the SED fitting technique for undetected sources in mid- and far-infrared observations. Using this unique sample, we conduct a comprehensive analysis of the dependence of the total SFR , total stellar masses and halo occupation distribution (HOD) of massive galaxies (M*>10^10 M_sun) on the halo mass of the groups with rigorous consideration of uncertainties. We observe a clear evolution in the level of star formation (SF) activity in galaxy groups. Indeed, the total star formation activity in high redshift (0.5

We present a study of the galaxy populations in massive galaxy clusters selected by their Sunyaev–Zel’dovich Effect (SZE) signatures. Selection via the SZE is approximately mass- limited where the mass limit varies only slightly with redshift, making it an ideal selection method for studying the evolution of the galaxy content of clusters. We begin by introducing the SZE, the South Pole Telescope (SPT), and the larger research project in which this Thesis is embedded. We then present the core galaxy population studies of this Thesis. In Chapter 3, we present the first large-scale follow-up of an SZE-selected galaxy cluster sample. Of 224 galaxy cluster candidates in the sample, we optically confirm 158 clusters and measure their photometric redshifts. We find a redshift range of 0.1

In dieser Arbeit wird ein schnelles Strahlungsmodell im sichtbaren Spektralbereich erstellt. Ausgehend vom von einem meteorologischen Modell berechneten Zustand der Atmosphäre ergibt dieses Strahlungsmodell die Strahldichte am oberen Rand der Atmosph äre, die ein Satellit messen würde, wenn die Atmosphäre tatsächlich so aussehen würde (synthetisches Satellitenbild). Der Vergleich mit einem tatsächlichen Satellitenbild gibt Hinweise über mögliche Fehler des meteorologischen Modells. Mehrere Forschungsrichtungen werden in dieser Arbeit untersucht. Das Endprogramm (pastat) basiert weitgehend auf Look-Up Tables. Eine Erweiterung der Eddington-Approximation bis auf die dritte Ordnung wird verwendet, um die azimutal gemittelte Strahldichte zu berechnen. Ein Ansatz mit 16 statistisch bestimmten Parametern bringt die notwendige azimutale Abhängigkeit. Das Genauigkeitskriterium für das zu erstellende Strahlungsmodell ist ein relativer Fehler der Re�ektivität unter 10% oder ein absoluter Fehler unter 0.02. Die Erfolgsrate von pastat hängt stark vom Sonnenzenitwinkel ab. Der mittlere relative Fehler von pastat ist eine Gröÿenordnung höher als der von den meisten vorhandenen schnellen Strahlungsmodellen im Infraroten. Im Sichtbaren bringt der Mehrfachstreuterm der Strahlungstransportgleichung nämlich eine erhebliche zusätzliche Erschwernis im Vergleich zum Infraroten. Jedoch wird das Erfolgskriterium in fast allen Fällen von pastat eingehalten. Somit erlaubt dieses Verfahren, Modellfehler auf 10% Genauigkeit zu detektieren. pastat ist das erste schnelle Strahlungsmodell im sichtbaren Spektralbereich für wolkige Atmosphären.

The work presented here focuses on the investigation and further development of simple mass estimators for early-type galaxies which are suitable for large optical galaxy surveys with poor and/or noisy data. We consider simple and robust methods that provide an anisotropy-independent estimate of the galaxy mass relying on the stellar surface brightness and projected velocity dispersion profiles. Under reasonable assumptions a fundamental mass-anisotropy degeneracy can be circumvented without invoking any additional observational data, although at a special (characteristic) radius only, i.e these approaches do not recover the radial mass distribution. Reliable simple mass estimates at a single radius could be used (i) to cross-calibrate other mass determination methods; (ii) to estimate a non-thermal contribution to the total gas pressure when compared with the X-ray mass estimate at the same radius; (iii) to evaluate a dark matter fraction when compared with the luminous mass estimate; (iv) to derive the slope of the mass profile when combined with the mass estimate from strong lensing; (v) or as a virial mass proxy. Two simple mass estimators have been suggested recently - the local (Churazov et al. 2010) and the global (Wolf et al. 2010) methods - which evaluate mass at a particular radius and are claimed to be weakly dependent on the anisotropy of stellar orbits. One approach (Wolf et al. 2010) uses the total luminosity-weighted velocity dispersion and evaluates the mass at a deprojected half-light radius, i.e. relies on the global properties of a galaxy. In contrast, the Churazov et al. technique uses local properties: logarithmic slopes of the surface brightness and velocity dispersion profiles, and recovers the mass at a radius where the surface brightness declines as R^{-2} (see also Richstone and Tremaine 1984, Gerhard 1993). To test the robustness and accuracy of the methods I applied them to analytic models and to simulated galaxies from a sample of cosmological zoom-simulations which are similar in properties to nearby early-type galaxies. Both local and global simple mass estimates are found to be in good agreement with the true mass at the corresponding characteristic radius. Particularly, for slowly rotating simulated galaxies the local method gives an almost unbiased mass-estimate (when averaged over the sample) with a modest RMS-scatter of 12% (Chapter 2). When applied to massive simulated galaxies with a roughly flat velocity dispersion profile, the global approach on average also provides the almost unbiased mass-estimate, although the RMS-scatter is slightly larger (14-20 %) than for the local estimator (Chapter 4). A noticeable scatter in the determination of the characteristic radius is also expected since the half-light radius depends on the radial range used for the analysis and applied methodology. Next I tested the simple mass estimators on a sample of real early-type galaxies which had previously been analyzed in detail using state-of-the-art dynamical modeling. For this set of galaxies the simple mass estimates are in remarkable agreement with the results of the Schwarzschild modeling despite the fact that some of the considered galaxies are flattened and mildly rotating. When averaged over the sample the simple local method overestimates the best-fit mass from dynamical modeling by 10% with the RMS-scatter 13% between different galaxies. The bias is comparable to measurement uncertainties. Moreover, it is mainly driven by a single galaxy which has been found to be the most compact one in the sample. When this galaxy is excluded from the sample, the bias and the RMS-scatter are both reduced to 6%. The global estimator for the same sample gives the mean deviation 4% with the slightly larger RMS-scatter of 15% (Chapter 4). Given the encouraging results of the tests I apply the local mass estimation method to a sample of five X-ray bright early-type galaxies observed with the 6-m telescope BTA in Russia. Using publicly available Chandra data I derived the X-ray mass profile assuming spherical symmetry and hydrostatic equilibrium of hot gas. A comparison between the X-ray and optical mass estimates allowed me to put constraints on the non-thermal contribution (sample averaged value is 4%) to the total gas pressure arising from, for instance, microturbulent gas motions. Once the X-ray derived circular speed is corrected for the non-thermal contribution, the mismatch between the X-ray circular speed V_c^X and the optical circular velocity for isotropic stellar orbits V_c^{iso} provides a clue to the orbital structure of the galaxy. E.g., at small radii V_c^X > V_c^{iso} would suggest more circular orbits, while at larger radii this would correspond to more radial orbits. For two galaxies in our sample there is a clear indication that at radii larger than the half-light radius stellar orbits become predominantly radial. Finally, the difference between the optical mass-estimate at the characteristic radius and the stellar contribution to the total mass permitted the derivation of a dark-matter fraction. A typical dark matter fraction for our sample of early-type galaxies is 50% for Salpeter IMF and 70% for Kroupa IMF at the radius which is close to the half-light radius (Chapter 3).

Fri, 21 Feb 2014 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/17301/ https://edoc.ub.uni-muenchen.de/17301/1/Ideguchi_Takuro.pdf Ideguchi, Takuro ddc:530, ddc:500, Fakultät für Physik

Wed, 12 Feb 2014 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/18240/ https://edoc.ub.uni-muenchen.de/18240/1/Marel_Anna-Kristina.pdf Marel, Anna-Kristina ddc:530, ddc:500, Fakultät

The search for exo-planets is currently one of the most exiting and active topics in astronomy. Small and rocky planets are particularly the subject of intense research, since if they are suitably located from their host star, they may be warm and potentially habitable worlds. On the other hand, the discovery of giant planets in short-period orbits provides important constraints on models that describe planet formation and orbital migration theories. Several projects are dedicated to discover and characterize planets outside of our solar system. Among them, the Wide-Field Camera Transit Survey (WTS) is a pioneer program aimed to search for extra-solar planets, that stands out for its particular aims and methodology. The WTS has been in operation since August 2007 with observations from the United Kingdom Infrared Telescope, and represents the first survey that searches for transiting planets in the near-infrared wavelengths; hence the WTS is designed to discover planets around M-dwarfs. The survey was originally assigned about 200 nights, observing four fields that were selected seasonally (RA = 03, 07, 17 and 19h) during a year. The images from the survey are processed by a data reduction pipeline, which uses aperture photometry to construct the light curves. For the most complete field (19h-1145 epochs) in the survey, we produce an alternative set of light curves by using the method of difference imaging, which is a photometric technique that has shown important advantages when used in crowded fields. A quantitative comparison between the photometric precision achieved with both methods is carried out in this work. We remove systematic effects using the sysrem algorithm, scale the error bars on the light curves, and perform a comparison of the corrected light curves. The results show that the aperture photometry light curves provide slightly better precision for objects with J < 16. However, difference photometry light curves present a significant improvement for fainter stars. In order to detect transits in the WTS light curves, we use a modified version of the box-fitting algorithm. The implementation on the detection algorithm performs a trapezoid-fit to the folded light curve. We show that the new fit is able to produce more accurate results than the box-fit model. We describe a set of selection criteria to search for transit candidates that include a parameter calculated by our detection algorithm: the V-shape parameter, which has proven to be useful to automatically identify and remove eclipsing binaries from the survey. The criteria are optimized using Monte-Carlo simulations of artificial transit signals that are injected into the real WTS light curves and subsequently analyzed by our detection algorithm. We separately optimize the selection criteria for two different sets of light curves, one for F-G-K stars, and another for M-dwarfs. In order to search for transiting planet candidates, the optimized selection criteria are applied to the aperture photometry and difference imaging light curves. In this way, the best 200 transit candidates from a sample of ~ 475 000 sources are automatically selected. A visual inspection of the folded light curves of these detections is carried out to eliminate clear false-positives or false-detections. Subsequently, several analysis steps are performed on the 18 best detections, which allow us to classify these objects as transiting planet and eclipsing binary candidates. We report one planet candidate orbiting a late G-type star, which is proposed for photometric follow-up. The independent analysis on the M-dwarf sample provides no planet candidates around these stars. Therefore, the null detection hypothesis and upper limits on the occurrence rate of giant planets around M-dwarfs with J < 17 mag presented in a prior study are confirmed. In this work, we extended the search for transiting planets to stars with J < 18 mag, which enables us to impose a more strict upper limit of 1.1 % on the occurrence rate of short-period giant planets around M-dwarfs, which is significantly lower than other limit published so far. The lack of Hot Jupiters around M-dwarfs play an important role in the existing theories of planet formation and orbital migration of exo-planets around low-mass stars. The dearth of gas-giant planets in short-period orbit detections around M stars indicates that it is not necessary to invoke the disk instability formation mechanism, coupled with an orbital migration process to explain the presence of such planets around low-mass stars. The much reduced efficiency of the core-accretion model to form Jupiters around cool stars seems to be in agreement with the current null result. However, our upper limit value, the lowest reported sofar, is still higher than the detection rates of short-period gas-giant planets around hotter stars. Therefore, we cannot yet reach any firm conclusion about Jovian planet formation models around low-mass and cool main-sequence stars, since there are currently not sufficient observational evidences to support the argument that Hot Jupiters are less common around M-dwarfs than around Sun-like stars. The way to improve this situation is to monitor larger samples of M-stars. For example, an extended analysis of the remaining three WTS fields and currently running M-dwarf transit surveys (like Pan-Planets and PTF/M-dwarfs projects, which are monitoring up to 100 000 objects) may reduce this upper limit. Current and future space missions like Kepler and GAIA could also help to either set stricter upper limits or finally detect Hot Jupiters around low-mass stars. In the last part of this thesis, we present other applications of the difference imaging light curves. We report the detection of five faint extremely-short-period eclipsing binary systems with periods shorter than 0.23 d, as well as two candidates and one confirmed M-dwarf/M-dwarf eclipsing binaries. The etections and results presented in this work demonstrate the benefits of using the difference imaging light curves, especially when going to fainter magnitudes.

Fri, 7 Feb 2014 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/19168/ https://edoc.ub.uni-muenchen.de/19168/1/Klein_Thomas.pdf Klein, Thomas ddc:530, ddc:500, Fakultät für Physik

Das Gebiet der Nichtgleichgewichtsdynamik stark korrelierter Quantensysteme beinhaltet eine Vielzahl interessanter Fragestellungen, erweist sich dabei allerdings oftmals als schwer zugänglich für gängige numerische und analytische mathematische Methoden. In den letzten Jahren hat sich durch die experimentelle Realisierung gut kontrollierbarer quantenmechanischer Systeme die Möglichkeit eröffnet, Experimente als Quantensimulatoren für das Verhalten komplexer Vielteilchensysteme zu benutzen. Ultrakalte Atome in optischen Gittern eignen sich hervorragend als Simulatoren für simple Festkörpersysteme, da sich sämtliche Parameter der zugrunde liegenden Hamiltonoperatoren präzise kontrollieren lassen und der Zustand der Systeme mit einer Vielzahl an Messmethoden untersucht werden kann. In unseren Experimenten realisieren wir Bose-Hubbard Systeme durch ultrakalte 39K Atome in blau verstimmten optischen Gittern. Zusätzliche optische Dipolpotenziale und magnetische Feshbach-Resonanzen erlauben es uns dabei, die Parameter der Systeme zu jedem Zeitpunkt beliebig zu variieren. Dadurch sind die von uns erzeugten Systeme in besonderem Maße dazu geeignet, Nichtgleichgewichtseffekte zu untersuchen. Unser Hauptaugenmerk liegt auf der Untersuchung der Expansionsdynamik wechselwirkender Atome in homogenen Gittern. Wir beginnen unsere Experimente mit einem Anfangszustand im tiefen Gitter, der aus lokalisierten Atomen auf maximal einfach besetzten Gitterplätzen besteht. Durch gleichzeitiges schnelles Verringern der Gittertiefe und der externen Potenziale werden die Atome in ein homogenes Gitter entlassen und die Zeitentwicklung ihrer Dichteverteilung wird durch Absorptionsabbildungen festgehalten. Es zeigt sich, dass sowohl die Wechselwirkung zwischen den Atomen als auch die Dimensionalität der Gitter einen starken Einfluss auf die Dynamik haben. In allen integrablen Grenzfällen des Bose-Hubbard Modells verhalten sich die Atome ballistisch und expandieren mit hoher Geschwindigkeit, doch sobald sich das System außerhalb der integrablen Regime befindet verringert sich die Expansionsgeschwind-igkeit drastisch. Diese verringerte Geschwindigkeit geht einher mit der Ausbildung charakteristischer bimodaler Dichteverteilungen, die auf eine diffusive Dynamik schließen lassen. Für stark wechselwirkende Systeme können wir einen dimensionalitätsabhängigen Übergang zwischen ballistischer Dynamik im 1D hard-core-regime und diffusiver Dynamik im 2D Fall beobachten sowie eine starke Verringerung der Expansionsgeschwindigkeit, wenn der Anfangszustand des Systems mehrfach besetzte Gitterplätze enthält. Des Weiteren beobachten wir die Erzeugung solcher Mehrfachbesetzungen nach dem Entlassen der Atome, deren schnelle Entwicklung auf eine lokale Relaxationsdynamik hin zu quasistationären Werten deuten lässt. Als Letztes untersuchen wir die Entwicklung der Quasiimpulsverteilung stark wechselwirkender expandierender Atome, die laut theoretischer Vorhersagen eine vorübergehende Quasikondensation zeigen sollen, bei der sich scharfe lokale Maxima in der Quasiimpulsverteilung bei endlichen Quasiimpulsen bilden. Wir beobachten die Entstehung nicht-thermischer Quasiimpulsverteilungen die Maxima an den vor-hergesagten Positionen zeigen. Allerdings sind die von uns beobachteten Maxima wesentlich breiter als die vorhergesagten und wir diskutieren eine Reihe möglicher Erklärungen für diese Verbreiterung sowie Vorschläge zur Verbesserung zukünftiger Experimente.

The majority of stars in the universe has formed in disc galaxies with masses similar to that of the Milky Way. Ab-initio cosmological hydrodynamical simulations of the formation and evolution of galaxies in a Lambda Cold Dark Matter universe have long suffered from serious problems in correctly modelling the star-formation history and structure of disc galaxies. We first use idealized semi-cosmological simulations to gain a better understanding of processes leading to problems in disc formation simulations. We add rotating spheres of hot gas to cosmological dark-matter-only simulations of individual haloes and follow the formation and evolution of galaxy discs from the cooling gas. The initial orientation of the baryonic angular momentum with respect to the halo has a major effect on disc formation. Despite the coherently rotating initial conditions, the orientations of the disc and the outer gas and the relative angle between the components can all change by more than 90 degrees over several billion years. Dominant discs with realistic structural and kinematical properties form preferentially if slow cooling times shift disc formation to later times, if the initial angular momentum is aligned with the halo minor axis and if there is little reorientation of the disc. We then present a new set of fully cosmological simulations with an updated multiphase smoothed particle hydrodynamics galaxy formation code. The update includes improved treatment of metal-line cooling, metal production, turbulent diffusion of metals, kinetic and thermal supernova feedback and radiation pressure from massive young stars. We compare the models to a variety of observations at high and low redshifts and find good agreement for morphologies, stellar-to-dark-matter mass ratios, star formation rates, gas fractions and heavy element abundances. Agreement is better at redshift z=1 than at present day as discrepancies in star formation histories for the lowest and highest simulated galaxy masses become apparent at late times. 18 out of 19 of our model galaxies at z=0 contain stellar discs with kinematic disc fractions up to 65 %, higher than in any previous simulations. We finally compare our model galaxies in detail with recent observations of the structural evolution of stellar galactic discs and the structure of z=0 gas discs. Stellar surface density profiles agree well with observations at z>1, but reveal too little central growth afterwards. This is likely connected to a lack of bars in our simulations resulting from overly strong feedback. Discs at z=0 are too extended by a factor sim 2. The discs have diverse formation histories ranging from pure inside-out growth in systems with quiescent merger histories to continuous mass growth at all radii. Central mass growth in our models is driven by mergers and misaligned infall events, which leave signatures in the present day distributions of radii and element abundances as functions of stellar age. Gas discs agree well with observations in terms of sizes and profile shapes, but on average have overly high gas-to-stellar mass ratios. Our models agree well with the observed neutral hydrogen mass-size relation. Despite significant progress, our models continue to suffer from various problems illustrating that we are still far away from capturing all relevant physical processes accurately.

Mon, 27 Jan 2014 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/16554/ https://edoc.ub.uni-muenchen.de/16554/1/Patalong_Peter.pdf Patalong, Peter ddc:530, ddc:500, Fakultät für Physik

Semiconducting single-walled carbon nanotubes (CNTs) exhibit a chirality depended band structure of a one-dimensional lattice. Due to the radiative recombination of excitons CNTs emit photoluminescence in the near and mid infrared ranges depending on the tube diameter. Excitons are subject to diffusion along the tube before radiative recombination. Thereby they probe sites that give rise to spin-flips or non-radiative decay, or, at cryogenic temperatures, they localize in zero-dimensional quantum dots at the minima of the local energy potential landscape. Thus, the optical spectroscopy of individual CNTs probes not only the intrinsic exciton dynamics, like diffusion and intrinsic life-time, but also disorder of the CNT lattice and its environment. Intrinsic and extrinsic inhomogeneities and impurities may give rise to photoluminescence quenching, brightening of dark exciton states or generation of charged exciton complexes. In the framework of this thesis the physics of excitons in CNTs was investigated in two ways: On the one hand their environment was varied with an static electric field, on the other hand the CNTs were isolated from their environment. A comprehensive set of optical spectroscopy techniques was used to study individual CNTs at low temperatures. This included photoluminescence excitation, (time-resolved) photoluminescence, and photon correlation spectroscopy. This work identified exciton localization as predominant feature of individual CNTs at cryogenic temperatures. CNTs on substrate exhibited asymmetric line shapes at low temperature and temperature dependent shifts on the PL energy. Moreover for constant temperature, PL energies were subject to spectral diffusion, which arose - in analogy to compound semiconductor quantum dots - from interaction with a few close charge fluctuators in the dielectric environment. In addition, evidence for exciton localization was provided by the non-classical photon emission statistics of cryogenic CNTs. The main focus of this thesis was the study of individual CNTs in a static electric field. A metal-oxide-semiconductor device was used to probe for the transverse polarizability of excitons. In consequence, the PL energy of CNTs exhibited red-shifts as a quadratic function of the perpendicular electric field. However, a subclass of CNTs was characterized by satellite peaks in the emission profile. By their energy splitting they were assigned to PL emission from dark exciton states, e.g. triplet and k-momentum excitons, and resulted presumably from impurity induced symmetry breaking. As a function of the electric field, CNTs with a broken symmetry featured linear shifts of the PL energy of bright and triplet excitons. A third energy scale in the exciton fine structure was manifested by CNTs that exhibited the emergence of a satellite peak as a function of the electric field. These satellites were assigned to the PL of trions generated by doping of individual CNTs with charges from close oxide states. Presumably such close charge states played also an important role in the variation of the excitation spectra of individual CNTs, which was observed as a function of the applied electric field. This variation could be mediated by switching of charge states, which varied the localization potential of excitons. Finally, the extrinsic effects of the surrounding dielectric medium were contrasted by the remarkable optical properties of as-grown suspended CNTs. Freely suspended CNTs featured isolated localized excitons with narrow linewidths, intrinsic exciton lifetime and a significantly increased quantum yield. Moreover, they lack signatures of spectral diffusion or intermittency even on the shortest timescales.

Diese Doktorarbeit umfasst zwei getrennte Analysen: zum einen die Messung des Verzweigungsverhaeltnisses B0 -> Psi(2S)Pi0 aus den Daten des Belle Experimentes, zum anderen die Abschaetzung der Rate von QED Untergrundereignissen bei kleinen Impulsen fuer das Detektorupgrade Belle II und deren Einfluss auf das Leistungsverhalten des neuen Pixeldetektors. In der ersten Analyse wurde der Zerfallskanal B0 -> Psi(2S)Pi0 untersucht und zum ersten Mal das zugehoerige Verzweigungsverhaeltnis bestimmt. Die Analyse beruht auf Daten des asymmetrischen e+e- KEKB Beschleunigers, die mit dem Belle Detektor aufgezeichnet wurden. Verwendet werden die gesamten Belle Daten, die 772 Millionen BbarB Paare enthalten. Die Analyse liefert folgendes Ergebnis fuer das Verzweigungsverhaeltnis: B(B0->Psi(2S)Pi0) = (1.07 +/- 0.23 +/- 0.08) x e-5. Die zweite Studie beschaeftigt sich mit dem Leistungsverhalten des Belle II Detektors. Viele Detektorkomponenten des Belle Experimentes werden im Ramen des Upgrades ersetzt oder verbessert. Wichtigste Veraenderung dabei ist der neue Pixeldetektor zur Messung des Wechselwirkungspunktes der kollidierenden Teilchen, der in unmittelbarer Naehe zum Strahlrohr eingebaut wird. Aufgrund seines geringen Radius wird er am staerksten von Untergrundereignissen beeinflusst. Es wird erwartet, dass zwei Photon QED Prozesse e+e- -> e+e-e+e- dabei die wichtigste Rolle spielen. Da die Luminositaet des neuen SuperKEKB Collider voraussichtlich 40-mal hoeher als die von KEKB sein wird, wird erwartet, dass die Rate von Untergrundereignissen entsprechend steigt. Um zwei Photon QED Prozesse zu analysieren, wurden Ereignisse verwendet, die nach dem Zufallsprinzip selektiert wurden (random trigger). Die bei diesen Ereignissen entstehenden Elektronen und Positronen haben eine sehr niedrige Energie und erreichen daher nur die innerste Lage des Pixeldetektors, die dadurch besonders belastet wird. Die Messungen zeigt, dass die Okkupanz der innersten Lage durch zwei Photon QED Ereignisse 0.7 % ist, was unterhalb der maximalen Okkupanz von 3 % liegt, bei der der Detektor noch fehlerfrei funktioniert.

Wed, 8 Jan 2014 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/16484/ https://edoc.ub.uni-muenchen.de/16484/1/Hofmann_Julian.pdf Hofmann, Julian ddc:530, ddc:500, Fakultät für Physik

Wed, 18 Dec 2013 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/16784/ https://edoc.ub.uni-muenchen.de/16784/1/Deeg_Andreas.pdf Deeg, Andreas

Wed, 18 Dec 2013 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/16936/ https://edoc.ub.uni-muenchen.de/16936/1/Folkerts_Sarah.pdf Folkerts, Sarah ddc:530, ddc:500, Fakultät für Physik

Wed, 18 Dec 2013 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/17353/ https://edoc.ub.uni-muenchen.de/17353/1/Buchner_Alexander.pdf Buchner, Alexander ddc:530, ddc:500, Fakultät für Physik

Durch moderne Laserspektroskopie ist es mittlerweile möglich, chemische Reaktionen mit einer Zeitauflösung von wenigen Femtosekunden zu untersuchen. Auf der anderen Seite kann die Molekülstruktur mithilfe von Röntgenstrukturanalyse sehr exakt bestimmt werden. Die vorliegende Doktorarbeit beschäftigt sich damit, diese beiden Gebiete zusammenzubringen. Der erste Teil der Dissertation beschreibt den Aufbau einer Laserplasmaquelle am Lehrstuhl für BioMolekulare Optik. Ein hochenergetischer Laserimpuls wird in einer Vakuumkammer auf ein Kupferband fokussiert. Dabei entsteht charakteristische Kupfer-K-alpha-Strahlung, die auf die kristalline Probe abgebildet wird. Ein zweiter Laserimpuls induziert in der Probe eine chemische Reaktion, die die Kristallstruktur ändert. Mit diesem Aufbau sind Röntgenbeugungsmessungen mit einer Zeitauflösung von wenigen hundert Femtosekunden möglich. An einem möglichen Probenkristall, DIABN, wurden zudem Transmissionsmessungen mit einer Röntgen-Streak-Kamera durchgeführt. Dieses Molekül zeigt einen Ladungstransferzustand auch in der kristallinen Phase, welcher mit einer Strukturänderung einhergeht. Der Ladungstransfer beeinflusst aber auch die Ausrichtung der umgebenden Moleküle, was die Extinktion des Kristalls stark verändert. Dieser Effekt kann mit zeitaufgelösten Transmissionsmessungen untersucht werden, bevor Röntgenbeugungsexperimente durchgeführt werden. Der Hauptteil der Dissertation handelt von der Excimerbildung in 9,10-Dichloroanthrazen (DCA). Mit zeitaufgelöster Emissions- und Absorptionsspektroskopie wurde zunächst das Verhalten in Lösung beobachtet. Hier konnte erstmals eine detaillierte Studie zur Konzentrationsabhängigkeit der Excimerbildung von DCA erstellt werden. Mit den dabei gewonnen Erkenntnissen konnte eine vergleichende Untersuchung der beiden Kristallformen, alpha und beta, durchgeführt werden. Entgegen andersartigen Darstellungen in der Literatur konnte gezeigt werden, dass in der alpha-Form keine Excimerbildung stattfindet, während für die beta-Form die Bildungsrate bei Raumtemperatur bestimmt werden konnte. Die experimentellen Befunde lassen sich wie folgt erklären: Während in Lösung die Bildungsrate mit der Konzentration steigt, da es ein diffusionskontrollierter Prozess ist, sind im Kristall die beteiligten Moleküle relativ starr im Kristallgitter fixiert. In der beta-Form verhindert die relative Anordnung der Moleküle eine Excimerbildung, wohingegen in der alpha-Form die Moleküle fast perfekt parallel ausgerichtet sind und innerhalb kürzester Zeit ein Excimer bilden. Dieses System ist eine ideale Probe für die neu aufgebaute Laserplasmaquelle.

Tue, 17 Dec 2013 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/16548/ https://edoc.ub.uni-muenchen.de/16548/1/Limmer_Katja.pdf Limmer, Katja ddc:530, ddc:500, Fakultät für Physik

Mon, 16 Dec 2013 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/16483/ https://edoc.ub.uni-muenchen.de/16483/1/Fietz_Sina.pdf Fietz, Sina ddc:530, ddc:500, Fakultät

Mon, 16 Dec 2013 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/16485/ https://edoc.ub.uni-muenchen.de/16485/1/Burckhart_Andreas.pdf Burckhart, Andreas ddc:530, ddc:500, Fakultät für Phy

Mon, 16 Dec 2013 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/17751/ https://edoc.ub.uni-muenchen.de/17751/1/Vernaleken_Andreas.pdf Vernaleken, Andreas ddc:530, ddc:500, Fakultät für Physik

Thu, 12 Dec 2013 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/16442/ https://edoc.ub.uni-muenchen.de/16442/1/Wienken_Uta.pdf Wienken, Uta ddc:530, ddc:500, Fakultät für Physik

The Carina Nebula Complex is known to be an active star-formation region. This work presents a large catalogue of point-like sources assembled from archive data of the Infrared Array Camera (IRAC) onboard the Spitzer Space Telescope. This catalogue covers a region of 2.3 deg × 3.0 deg, which makes it the most extendended mid-infrared survey undertaken of the Carina Nebula Complex to date. From the catalogue a subsample of candidate young stellar objects is extracted utilising the fact that young stellar objects exhibit typical mid-infrared excesses. These catalogues are employed to characterise the young stellar population of the Carina Nebula Complex. Using them, it was possible to identify three new extended green objects and five compact green objects and find the probable sources for 28 further objects connected with jets emitted from young stars, such as molecular hydrogen emission-line objects and Herbig-Haro jets. For 17 of them, observational data from the near-infrared (from HAWK-I and 2MASS) to the far-infrared (from the Herschel Space Observatory) could be collected and their spectral energy distributions fitted. From the fit parameters, stellar characteristics such as stellar and disk masses could be estimated. No young stellar objects with masses above 10 M_sol could be evidenced, pointing towards an intermediate-mass population currently forming. It could be shown that the Gum 31 region on the outer periphery of the Carina Nebula Complex is not only part of the complex but also an important centre of star formation. A large sample of candidate young stellar object was obtained from the WISE All-Sky Data Release, which allowed a detailed comparison with both the candidate young stellar objects from the IRAC catalogue and those identified from Herschel observations. Evidence could be found that two modes of triggered star formation are going on in the HII region: Young stellar objects are found in and in front of dust pillars, which is an indicator of radiative triggering, and a ‘collect and collapse’ model of the region was shown to produce results in agreement with the observations. An objective and large-scale search for clusters of young stellar objects in the complex was performed using a nearest-neighbour algorithm. This search derived 22 clusters not described before. Nine of those are new detections in the fields of previous studies of clusters while the majority are found in fields surveyed for clusters for the first time here. Clusters are also found in agreement with previous studies where study fields overlap, thus corroborating the validity of the study. It is found that ∼40% of the young stellar objects in the Carina Nebula Complex occur in clusters while up to 60% are part of a distributed population. A total population for the 2.3 deg × 3.0 deg study field of ∼200 000 young stars is estimated.

Wed, 11 Dec 2013 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/17931/ https://edoc.ub.uni-muenchen.de/17931/1/Prinz_Tobias.pdf Prinz, Tobias ddc:

The morphological analysis of galaxy clusters in X-rays allows a reliable determination of their dynamical state. Substructures on (sub-)Mpc scale influence the gravitational potential of a cluster and manifest themselves in the X-ray surface brightness distribution as secondary peaks or overall irregular shape. They lead to deviations from the hydrostatic equilibrium and spherical shape, two assumptions which are widely used in galaxy cluster studies to derive global astrophysical properties. Analyzing the X-ray morphology of clusters thus yields valuable information, provided that the employed substructure measures are well-tested and well-calibrated. In this work, the X-ray morphology of galaxy clusters is quantified using three common substructure parameters (power ratios, center shift and the asymmetry parameter), which are subsequently employed to study the disturbed cluster fraction as a function of redshift. To ensure a reliable application of these substructure parameters on a variety of X-ray images, a detailed parameter study is conducted. It focuses on the performance and reliability of the parameters for varying data quality using simulated and observed X-ray images. In particular, when applying them to X-ray images with low photon counts such as observations of distant clusters or survey data, it is important to know the characteristics of the parameters. Comparing the three substructure measures, the center shift parameter is most robust against Poisson noise and allows a reliable determination of the clusters' dynamical state even for low-count observations. Power ratios, especially the hexapole P3/P0, and the asymmetry parameter, on the other hand, are severely affected by noise, which results in spuriously high substructure signals. Furthermore, this work presents methods to minimize the noise bias. The results of the parameter study provide a step forward in the morphological analysis of high-redshift clusters and are employed in the framework of this thesis to quantify the evolution of the disturbed cluster fraction. The sample used for this analysis comprises 78 low-z (z < 0.3) and 51 high-z (0.3 < z < 1.08) galaxy clusters with varying photon statistics. The low-redshift objects were observed with the XMM-Newton observatory, contain a high number of photon counts and are part of several well-known and representative samples. For z > 0.3, the high-redshift subsets of the 400d2 and SPT survey catalog are used. These objects were mainly observed with the Chandra observatory and have low photon counts. To ensure a fair comparison, which is independent of the data quality, the photon statistics of the low- and high-redshift observations are aligned before performing the morphological analysis. In agreement with the hierarchical structure formation model, a mild positive evolution with redshift, i.e. a larger fraction of clusters with disturbed X-ray morphologies at higher redshift, is found. Owing to the low photon counts and small number of high-redshift observations, the statistical significance of this result is low. For two of the three substructure parameters (power ratios and center shift) the findings are also consistent within the significance limits with no evolution, but a negative evolution of the disturbed cluster fraction can be excluded for all parameters.

Idealized numerical model experiments are presented to investigate the convective generation of vertical vorticity in a tropical depression. The calculations are motivated by observations made during the recent PREDICT field experiment to study tropical cyclogenesis, and by a desire to understand the aggregation of vorticity debris produced by deep convection in models of tropical cyclogenesis to form a monopole vortex. One aim is to isolate and quantify the effects of low to mid level dry air on convective cells that form within a depression and, in particular, on the generation of vertical vorticity in these cells. Another aim is to isolate the effects of a unidirectional boundary layer wind profile on storm structure, especially on vertical vorticity production and updraught splitting, and the combined effects of horizontal and vertical shear on vertical vorticity production, with and without background rotation. A third aim is to isolate the effects of a vortex boundary-layer wind profile on tropical deep convection, focussing especially on the morphology of vertical vorticity that develops. The growing convective updraughts, that are initiated by a near surface thermal perturbation, amplify locally the ambient rotation at low levels by more than an order of magnitude and this vorticity persists long after the updraught has decayed, supporting the results of an earlier study. The results of calculations with dry air aloft do not support a common perception that the dry air produces stronger downdraughts. In calculations where the vertical wind shear changes sign at some level near the top of the boundary layer, as occurs in warm-cored disturbances such as tropical depressions or tropical cyclones, it was found that the tilting of horizontal vorticity by a convective updraught leads not only to dipole patterns of vertical vorticity, but also to a reversal in sign of the updraught rotation with height. This feature is quite unlike the structure in a typical middle-latitude `supercell' storm. These results provide an essential first step to understanding the interaction between deep convective elements in a tropical depression or tropical cyclone. An increase in the magnitude of boundary-layer shear was found to have the dual effect of weakening the development of the initial thermal, which is detrimental to vertical vorticity production by stretching and tilting, while at the same time increasing the magnitude of horizontal vorticity that can be tilted. The results provide a basis for appraising a recent conjecture concerning the role of storm splitting in explaining the contraction of the eyewall in tropical cyclones.

Fri, 6 Dec 2013 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/17388/ https://edoc.ub.uni-muenchen.de/17388/1/Agarwal_Bhaskar.pdf Agarwal, Bhaskar ddc:530, ddc:500, Fakultät für

Wed, 4 Dec 2013 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/16417/ https://edoc.ub.uni-muenchen.de/16417/1/Beck_Alexander_M.pdf Beck, Alexander Maximilian ddc:530, ddc:500, Fakultät für Physik

Mon, 2 Dec 2013 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/16366/ https://edoc.ub.uni-muenchen.de/16366/1/Wuersch_Michael.pdf Würsch, Michael ddc:530, ddc:500, Fakult

Mon, 2 Dec 2013 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/16680/ https://edoc.ub.uni-muenchen.de/16680/1/Alig_Christian.pdf Alig, Christian ddc:530, ddc:500, Fakultät für Physik

Mon, 2 Dec 2013 12:00:00 +0100 https://edoc.ub.uni-muenchen.de/17085/ https://edoc.ub.uni-muenchen.de/17085/1/Shao_Li.pdf Shao, Li ddc:530, ddc:500, Fakultät für Physik

Cirrus cloud genesis is a multiscale problem. This makes the parameterization in numerical weather prediction models a challenging task. In order to improve the prediction of cirrus clouds and ice supersaturation formation in the German Weather Service (DWD) model chain, the controlling physical processes are investigated and parameterised in a new cloud ice microphysics scheme. Scale dependencies of the ice microphysical scheme were assessed by conducting simulations with an idealised and realistic regional Consortium for Small-Scale Modeling (COSMO) model setup and a global model (GME). The developed two-moment two-mode cloud ice scheme includes state-of-the-art parameterisations for the two main ice creating processes, homogeneous and heterogeneous nucleation. Homogeneous freezing of supercooled liquid aerosols is triggered in regions with high atmospheric ice supersaturations (145-160 %) and high cooling rates. Heterogeneous nucleation depends mostly on the existence of sufficient ice nuclei in the atmosphere and occurs at lower ice supersaturations. The larger heterogeneously nucleated ice crystals can deplete ice supersaturation and inhibit subsequent homogenenous freezing. In order to avoid an overestimation of heterogeneous nucleation, cloud ice sedimentation and a prognostic budget variable for activated ice nuclei are introduced. A consistent treatment of the depositional growth of the two ice particle modes and the larger snowflakes using a relaxation timescale method was applied which ensures a physical representation for depleting ice supersaturation. Comparisons between the operational and the new cloud ice microphysics scheme in the GME revealed that the location of cirrus clouds is dominated by the model dynamics whereas the cirrus cloud structures strongly differed for the different schemes. Especially a reduction in the ice water content between 9 and 11 km was observed when using the new cloud ice scheme. This change is an improvement as demonstrated by a comparison with the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) ice water content product. Further comparisons of the GME with the Integrated Forecast System (IFS) model of the European Centre for Medium-Range Weather Forecasts (ECMWF) show a clear improvement of the ice supersaturation distribution with the new two-moment cloud ice scheme. In-cloud ice supersaturation is correctly captured, which is compliant with in-situ measurements. This is a more physical description then in the IFS model, where in-cloud ice saturation is assumed.