The goal of this thesis is to gain theoretical understanding of the distribution of dust and gas in the innermost parsecs of Active Galactic Nuclei. Unified schemes demand a circum-nuclear disk or "torus" to geometrically unify two separate classes of observed objects (face-on and edge-on view onto the torus). In a multi-step approach, we work towards the establishment of realistic simulations of this massive and dense gas and dust reservoir, in order to be able to interpret near- and mid-infrared interferometric observations (MIDI, AMBER), which are able to resolve dust structures in the centres of Seyfert galaxies. In a first step, we investigate an analytical torus model (the so-called "Turbulent Torus Model") with the help of radiative transfer calculations and find gross agreement with large aperture, as well as high-resolution observations of Seyfert galaxies. However, the model SEDs show too pronounced silicate emission features in the face-on case. This can be overcome with the help of three-dimensional clumpy tori, calculated in a second step. Special emphasis is put on the differences of clumpy and continuous dust distributions, also concerning interferometric observations. In a further step, we apply hydrodynamic simulations to trace the evolution of a nuclear star cluster, which provides energy via discrete supernova explosions and mass from stellar mass loss. With these ingredients, a highly dynamical system forms, with gas streaming inward, in form of long filaments, which cool due to radiative energy losses. In the vicinity of the minimum of the effective potential (caused by gravity of the nuclear stellar cluster and black hole, as well as rotation of the gas), a turbulent disk forms, surrounded by a less dense clumpy and filamentary toroidal structure. Subsequent radiative transfer calculations yield good agreement with Seyfert galaxy spectral energy distributions (observed with the Spitzer space telescope). Problems of the comparison of continuous models with the silicate feature strength to H I column density relation can be overcome with the help of our new approach.
Ich benutze HST-Bilder des Projektes GEMS und photometrische Rotverschiebungen von COMBO-17, um die Rolle von blauen elliptischen Galaxien (BSGs) und die Entwicklung von scheiben-dominierten Galaxien seit einer Rotverschiebung von z~1 zu untersuchen. Um meine Galaxienauswahl treffen zu können, habe ich GALFIT und GIM2D, zwei oft angewandte 2-D Modellierungs-Programme, intensiv auf echten und simulierten Daten getestet. Ich zeige, daß GALFIT zuverlässigere Ergebnisse liefert als GIM2D, vor allem durch seine Fähigkeit, benachbarte Objekte gleichzeitig anzupassen. Beide Programme unterschätzen die Fehlerbalken der Parameter dabei stark. Durch automatische Klassifikation sowie durch Klassifikation per Auge, gewinne ich eine Auswahl an BSGs und zeige, daß nur BSGs mit hoher Massendichte in der Lage sind, sich passiv in typische rote elliptische Galaxien zu entwickeln, und daß ca. ~6% der massereichen elliptischen Galaxien blaue Färbung zeigen, in Übereinstimmung mit Vorhersagen aus Zusammenstoß-Raten von Galaxien. Für Scheiben-Galaxien finde ich eine starke Entwicklung der Helligkeit–Größe-Beziehung von Galaxien mit M_V <~ -20, entsprechend einer Zunahme der Helligkeit von ca. 1 mag arcsec^-2 im V -Band seit z~1. Nur schwache oder keine Entwicklung der Masse-Größe-Beziehung von Galaxien mit log(M/M_sun)>~10 ist sichtbar im gleichen Zeitraum, konsistent mit einem mittleren Wachstum der Scheiben von Innen nach Außen. Scheiben werden umso größer, je massereicher sie werden.
At less than 4 Mpc away, Centaurus A (NGC 5128) is the nearest massive elliptical galaxy, the nearest radio galaxy, and the nearest recent merger. It is the ideal laboratory to study the connection between merging, massive black holes, the source of radio jets, and merger-induced star formation in detail. Using Naos-Conica and SINFONI at the ESO Very Large Telescope (VLT), we obtained adaptive optics (AO) assisted data at unprecedented spatial resolution. We demonstrate that thorough kinematical modelling of AO data is feasible and leads to an accurate measurement of the black hole mass. We find that depending on their ionisation level, different gas species display different flux distributions and velocity structures. In this respect, integral-field-unit data are crucial to identify non-gravitational gas motions. The H2 gas kinematics inside the central r<1.5 arcsec of the active galactic nucleus are successfully described by a (warped) gas disk, rotating in the joint gravitational potential of the stars and a black hole of Mbh~7x10^7 Msolar. With our revised Mbh estimate, that is a factor ~3 lower than previous measurements, Cen A is no longer a dramatic outlier in the Mbh-sigma relation. Near-infrared images in JHK reveal marginally resolved stellar clusters, comparable in their properties to young starburst clusters found close to the Galactic Centre.
Turbulence in Earth's atmosphere severely limits the image quality of ground-based telescopes. With the technique of Adaptive Optics, the induced distortions of the light can be measured and corrected in real-time, regaining nearly diffraction-limited performance. Unfortunately, when using a single guide star to measure the distortions, the correction is only useful within a small angular area centered on the guide star. The first part of this thesis presents a laboratory setup, which uses four guide stars to measure the turbulence-induced distortions and one deformable mirror to correct the most turbulent layer. With such a Layer-Oriented Ground-Layer Adaptive Optics (GLAO) system, the area of useful correction is significantly increased. The system is characterized in static and dynamic operation, and the influence of non-conjugated turbulent layers, the effect of brightness variations of the guide-stars and the impact of misalignments are studied. Furthermore, calibration strategies and the performance of the Kalman control algorithm are examined. The second part of this thesis focuses on SCIDAR measurements of the atmospheric turbulence above Mt. Graham. This dataset provides for the first time a statistical and thorough analysis of the vertical turbulence structure above the LBT site. Based on 16 nights of measurements, spread over one year, Mt. Graham appears to be an excellent site for an astronomical observatory. By extending an analytical model, describing the filtering of the turbulence-induced distortions by an AO system, we calculate performance expectations of the LINC-NIRVANA instrument. In particular, the optimal conjugation heights of the deformable mirrors are studied. Furthermore, we present a new method to measure the atmospheric turbulence near the ground with 40 times increased vertical resolution, compared to standard SCIDAR. First on-sky results demonstrate the power of this technique.
HIROCS is a multi-color survey designed to construct a statistically significant galaxy cluster sample for galaxy evolution studies using a multi-color classification scheme in the redshift range 0.5 < z < 1.5. After contributing to the survey specifications, tests of the multi-color classification with the observational setup showed the feasibility of the project. The photometric redshift accuracy of delta(z) = 0.076 was estimated at the R band limit of ~25 mag. The new algorithm for the galaxy cluster detection was developed and tested with COMBO-17 data. In the three COMBO-17 fields covering 0.78 square degrees 15 cluster candidates were identified in the redshift range 0.3 < z < 0.9. The power of the search method was demonstrated by a comparison with the cluster detections from the Voronoi tessellation. For the determination of the cluster selection function in HIROCS and COMBO-17 procedures to simulate galaxy clusters were introduced. Due to the lack of fully reduced HIROCS data, the COMBO-17 selection function was quantified; rich clusters are expected to be found in the redshift range covered by COMBO-17. First steps towards an analysis of cluster candidates were carried out using the COMBO-17 candidates. Finally, a rich cluster at redshift ~0.7 was identified in the first HIROCS infrared data.
This thesis presents observational and theoretical studies of the size and spatial distribution of dust particles in circumstellar disks. Using millimetre interferometric observations of optically thick disks around T Tauri stars, I provide conclusive evidence for the presence of millimetre- to centimetre-sized dust aggregates. These findings demonstrate that dust grain growth to pebble-sized dust particles is completed within less than 1 Myr in the outer disks around low-mass pre-main-sequence stars. The modelling of the infrared spectral energy distributions of several solar-type main-sequence stars and their associated circumstellar debris disks reveals the ubiquity of inner gaps devoid of substantial amounts of dust among Vega-type infrared excess sources. It is argued that the absence of circumstellar material in the inner disks is most likely the result of the gravitational influence of a large planet and/or a lack of dust-producing minor bodies in the dust-free region. Finally, I describe a numerical model to simulate the dynamical evolution of dust particles in debris disks, taking into account the gravitational perturbations by planets, photon radiation pressure, and dissipative drag forces due to the Poynting-Robertson effect and stellar wind. The validity of the code it established by several tests and comparison to semi-analytic approximations. The debris disk model is applied to simulate the main structural features of a ring of circumstellar material around the main-sequence star HD 181327. The best agreement between model and observation is achieved for dust grains a few tens of microns in size locked in the 1:1 resonance with a Jupiter-mass planet (or above) on a circular orbit.