Spectroscopic studies on AGNs and High angular resolution in the NIR: The construction of an imaging beam combiner for the LBT

The current thesis is divided into two projects. The first part deals with studies on active galaxies hosting an Active Galactic Nucleus (AGN). Specifically, an optical spectroscopic study of a nearby (z < 0.06) volume - limited sample of Low - Luminosity Quasi - Stellar Objects (LLQSOs) has been carried out. The sample has been drawn from the Hamburg/ESO QSO survey (HES), which has a well-defined flux limit of B_j < 17.3. The aim of the present project is to characterize the excitation degree of the sample, distinguish between possible star forming and Seyfert activity and to investigate the spectral characteristics of the sample. The spectroscopic data were analyzed and emission lines were fitted using a routine, which employs Levenberg - Marquardt least square minimization. The same analysis was also applied for some additional archival data from the 6 Degree Field Galaxy Survey (6dFGS). The objects of the LLQSOs sample are classified according to the classical optical diagnostic diagrams, based on optical emission lines close in wavelength, avoiding almost any impact of reddening. The diagrams provide a diagnosis of the ionizing source within a galaxy, hence activity between Hii, LINERs (Low Ionization Nuclear Emission-line Region), and Seyfert galaxies can be clearly distinguished. The classification of all members of the LLQSOs sample is shown in chapter 3. The broadness of the emission lines, cases with double components and the electron density are also analyzed. The comparison of the diagnostic diagrams between the two data sets (HES and 6DFGS) results in different classifications of most of the sources. This is due to the different spectroscopic techniques applied in the two data sets during the observations, and is sketched in chapter 4. Several galaxies at a variety of cosmological distances, with elliptical and circular morphologies, were simulated. In these simulations, different instruments (different spectroscopic techniques, i.e. slit, fiber) were applied to the galaxies, in order to study the instrumental effect (aperture effect). The impact of the aperture effect in local and high redshift universe is discussed in detail. The second project of the thesis focuses on the construction of an image beam combiner for the Large Binocular Telescope (LBT). The LINC - NIRVANA instrument will be operating in the near - infrared (1 - 2.4 μm) and will provide a high angular resolution (~9 mas at 1.25 μm) over a wide field of view (~100 arcsec at 1.25 μm). A fundamental component of the instrument, the Fringe and Flexure Tracking System (FFTS) is responsible to ensure a complete and time-stable wavefront correction at the position of the science detector. This will allow for long integration times at interferometric angular resolutions. A historical overview and our current achievements are also discussed in chapter 5. Laboratory tests of specific parts of the FFTS are presented in chapter 6. Especially, the subparts of the Detector Positioning Unit (DPU), which has to be moved with respect to an altitude - azimuth mounting under vacuum conditions, are characterized. The tilting of the instrument as a function of elevation results in a flexure of the system that has to be corrected by an algorithm

Galaxy density profiles and shapes -- I. simulation pipeline for lensing by realistic galaxy models

Studies of strong gravitational lensing in current and upcoming wide and deep photometric surveys, and of stellar kinematics from (integral-field) spectroscopy at increasing redshifts, promise to provide valuable constraints on galaxy density profiles and shapes. However, both methods are affected by various selection and modelling biases, whch we aim to investigate in a consistent way. In this first paper in a series we develop a flexible but efficient pipeline to simulate lensing by realistic galaxy models. These galaxy models have separate stellar and dark matter components, each with a range of density profiles and shapes representative of early-type, central galaxies without significant contributions from other nearby galaxies. We use Fourier methods to calculate the lensing properties of galaxies with arbitrary surface density distributions, and Monte Carlo methods to compute lensing statistics such as point-source lensing cross-sections. Incorporating a variety of magnification bias modes lets us examine different survey limitations in image resolution and flux. We rigorously test the numerical methods for systematic errors and sensitivity to basic assumptions. We also determine the minimum number of viewing angles that must be sampled in order to recover accurate orientation-averaged lensing quantities. We find that for a range of non-isothermal stellar and dark matter density profiles typical of elliptical galaxies, the combined density profile and corresponding lensing properties are surprisingly close to isothermal around the Einstein radius. The converse implication is that constraints from strong lensing and/or stellar kinematics, which are indeed consistent with isothermal models near the Einstein radius, cannot trivially be extrapolated to smaller and larger radii.Comment: 31 pages, 15 figures; paper II at arXiv:0808.2497; accepted for publication in MNRAS; PDF file with full resolution figures at http://www.sns.ias.edu/~glenn/paper1.pd

Nuclei of Nearby Active Galaxies: NIR and Sub-mm Views and Finalizing the LINC-NIRVANA Fringe and Flexure Tracking System: Flexure and Temperature Behavior

The work presented in my thesis addresses the two cornerstones of modern astronomy: Observation and Instrumentation. Part I deals with the observation of two nearby active galaxies, the Seyfert 2 galaxy NGC 1433 and the Seyfert 1 galaxy NGC 1566, both at a distance of $\sim10$ Mpc, which are part of the Nuclei of Galaxies (NUGA) sample. It is well established that every galaxy harbors a super massive black hole (SMBH) at its center. Furthermore, there seems to be a fundamental correlation between the stellar bulge and SMBH masses. Simulations show that massive feedback, e.g., powerful outflows, in Quasi Stellar Objects (QSOs) has an impact on the mutual growth of bulge and SMBH. Nearby galaxies follow this relation but accrete mass at much lower rates. This gives rise to the following questions: Which mechanisms allow feeding of nearby Active Galactic Nuclei (AGN)? Is this feeding triggered by events, e.g., star formation, nuclear spirals, outflows, on $\sim500$ pc scales around the AGN? Does feedback on these scales play a role in quenching the feeding process? Does it have an effect on the star formation close to the nucleus? To answer these questions I have carried out observations with the Spectrograph for INtegral Field Observation in the Near Infrared (SINFONI) at the Very Large Telescope (VLT) situated on Cerro Paranal in Chile. I have reduced and analyzed the recorded data, which contain spatial and spectral information in the H-band (1.45 \mic-1.85 \mic) and K-band (1.95 \mic-2.45 \mic) on the central 10\arcsec\times10\arcsec of the observed galaxies. Additionally, Atacama Large Millimeter/Sub-millimeter Array (ALMA) data at $350$ GHz ($\sim0.87$ mm) as well as optical high resolution Hubble Space Telescope (HST) images are used for the analysis. For NGC 1433 I deduce from comparison of the distributions of gas, dust, and intensity of highly ionized emission lines that the galaxy center lies $\sim70$ pc north-northwest of the prior estimate. A velocity gradient is observed at the new center, which I interpret as a bipolar outflow, a circum nuclear disk, or a combination of both. At least one dust and gas arm leads from a $r\sim200$ pc ring towards the nucleus and might feed the SMBH. Two bright warm H$_2$ gas spots are detected that indicate hidden star formation or a spiral arm-arm interaction. From the stellar velocity dispersion (SVD) I estimate a SMBH mass of $\sim1.74\times10^7$ \msol. For NGC 1566 I observe a nuclear gas disk of $\sim150$ pc in radius with a spiral structure. I estimate the total mass of this disk to be $\sim5.4\times10^7$ \msol. What mechanisms excite the gas in the disk is not clear. Neither can the existence of outflows be proven nor is star formation detected over the whole disk. On one side of the spiral structure I detect a star forming region with an estimated star formation rate of $\sim2.6\times10^{-3}$ \msol\ yr$^{-1}$. From broad Br$\gamma$ emission and SVD I estimate a mean SMBH mass of $\sim5.3\times10^6$ \msol\ with an Eddington ratio of $\sim2\times10^{-3}$. Part II deals with the final tests of the Fringe and Flexure Tracker (FFTS) for LBT INterferometric Camera and the NIR/Visible Adaptive iNterferometer for Astronomy (LINC-NIRVANA) at the Large Binocular Telescope (LBT) in Arizona, USA, which I conducted. The FFTS is the subsystem that combines the two separate beams of the LBT and enables near-infrared interferometry with a significantly large field of view. The FFTS has a cryogenic system and an ambient temperature system which are separated by the baffle system. I redesigned this baffle to guarantee the functionality of the system after the final tests in the Cologne cryostat. The redesign did not affect any scientific performance of LINC-NIRVANA. I show in the final cooldown tests that the baffle fulfills the temperature requirement and stays $273$ K, which was not given for the old baffle design. Additionally, I test the tilting flexure of the whole FFTS and show that accurate positioning of the detector and the tracking during observation can be guaranteed

Experimental Benchmarks and Initial Evaluation of the Performance of the PASM System Prototype

The work reported here represents experiences with the PASM parallel processing system prototype during its first operational year. Most of the experiments were performed by students in the Fall semester of 1987. The first programming, and the first timing measurements, were made during the summer of 1987 by Sam Fineberg. The goal of the collection of experiments presented here was to undertake an Application-driven Architecture Study of the PASM system as a paradigm for parallel architecture evaluation in general. PASM was an excellent vehicle for experimenting with this evaluation technique due to its unique architectural features. Among these are: 1. A reconfigurable, partitionable multistage circuit-switched network. 2. Support for both SIMD and MIMD programs. 3. Ability to execute hybrid SIMD/MIMD programs. 4. An instruction queue which allows overlap of control-flow and data manipulation between micro-control (MC) units and processing elements (PE). It had been hypothesized that superlinear speed-up over the number of PEs could be attained with this feature, and experimental results verified this. 5. Support for barrier synchronization of MIMD tasks. This feature was exploited in some non-standard ways to show the ability to decouple variant length SIMD instructions into multiple MIMD streams for an overall performance benefit. This type of study is expected to continue in the future on PASM and other parallel machines at Purdue. This report should serve as a guide for this future work as well

Turbulent disruptions from the Strauss equations

The subject of this thesis is an analysis of results from pseudospectral simulation of the Strauss equations of reduced three-dimensional magnetohydrodynamics. We have solved these equations in a rigid cylinder of square cross section, a cylinder with perfectly conducting side walls, and periodic ends. We assume that the uniform-density magnetofluid which fills the cylinder is resistive, but inviscid. Situations which we are considering are in several essential ways similar to a tokamak-like plasma; an external magnetic field is imposed, and the plasma carries a net current which produces a poloidal magnetic field of sufficient strength to induce current disruptions. These disruptions are characterized by helical m = 1, n = 1 current filaments which wrap themselves around the magnetic axis. An ordered, helical velocity field grows out of the broad-band, low amplitude noise with which we initialize the velocity field. Kinetic energy peaks near the time the helical current filament disappears, and the current column broadens and is flattens itself out. We find that this is a nonlinear, turbulent phenomenon, in which many Fourier modes participate. By raising the Lundquist number used in the simulation, we are able to generate situations in which multiple disruptions are induced. When an external electric field is imposed on the plasma, the initial disruption, from a quiescent, state, is found to be very similar to those observed in the undriven runs. After the lobed m = 1, n = 1 stream function pattern develops, however, a quasi-steady state with flow is maintained for tens of Alfven transit times. If viscous damping is included in the driven problem, the steady state may be avoided, and additional disruptions produced in a time less than a large-scale resistive decay time

A New Atomization Paradigm: Smart Wave-Augmented Varicose Explosions

The characterization of viscous, non-Newtonian slurry heating and atomization by means of internal wave excitation is presented for a twin-fluid injector. We detail mechanisms that enhance their disintegration in a novel process called “Wave-Augmented Varicose Explosions” (WAVE). Atomization of such fluids is challenging, especially at low gas-liquid mass ratios. Droplet production is further complicated when slurry viscosity varies widely; if viscosity levels are too high, atomization quality suffers, and an undesirable pressure drop restricts the flow. To mitigate, we introduce and demonstrate “Smart” atomization, a novel implementation of simultaneous proportional integral derivative (PID) control algorithms to accommodate dynamically and extensively changing fluid properties. Unlike a conventional twin-fluid injector, WAVE injects a cold annular slurry flow into a hot core steam flow, encouraging regular slurry waves to form inside the nozzle and producing bulk system pulsation at 1000 Hz. The Kelvin-Helmholtz instability dominates during wave formation, while transonic pressure effects dominate during wave collapse. Numerical simulations reveal three atomization mechanisms that are a direct result of wave formation: 1) wave impact momentum, 2) pressure buildup, and 3) droplet breakaway. The first two are the forces that exploit slurry irregularities to drive rupture. The third occurs as rising waves penetrate the central steam flow and droplets are stripped off. Two effervescent mechanisms are also provided as 1) surface deformation allows steam fingers to force through the wave, and 2) the wave collapses on itself, trapping steam. Both Rayleigh-Taylor and Kelvin-Helmholtz instabilities are self-amplified in a viscosity-shear-temperature instability cycle because the slurry’s viscosity is sensitive to both strain and temperature. Smart atomization is applied to the WAVE framework with two coupled PID controllers to improve atomization robustness. The first controller automates slurry flow based on atomizer pressure drop, while the second compensates for the newly adjusted phase momentum ratio and sets a new steam flow based on droplet size. Three tests with increasingly rigorous models were conducted to capture the response of this coupled controller system to a step increase in viscosity. Though atomization characteristics were drastically altered, for a 100-fold increase in slurry viscosity, the controllers successfully maintained consistent droplet size and slurry flow resistance

Broadband Multilevel Fast Multipole Methods

Numerical simulations of electromagnetic fields are very important for a plethora of modern applications like antenna design, wireless communication systems, optical systems, high-frequency circuits and so on. As a consequence, there is much interest in finding algorithms that make these simulations as computationally efficient as possible. One of the leading classes of algorithms consists of the so-called Fast Multipole Methods. These methods use a subdivision of the geometry into boxes on multiple levels, in combination with a decomposition of the Green function. For high frequency simulations, where the wavelength is smaller then the smallest features of the geometry, a propagating plane wave decomposition leads to a very efficient algorithm. Unfortunately, this decomposition fails when the geometry contains features smaller than the wavelength, which is the case for broadband simulations. Broadband simulations are becoming increasingly important, for example in the simulation of high frequency printed circuit boards and microwave circuits, metamaterials or the scattering of radar waves off complex shapes. Because of the failure of the propagating plane wave decomposition, performing broadband simulations requires the construction of a hybrid algorithm which uses the propagating plane wave decomposition when the boxes are large enough and some low frequency decomposition when they are not. However, the known low frequency decompositions are usually suboptimal compared to the theoretical performance of the propagating plane wave decomposition. In this work, the focus will be on these low frequency decompositions. First, an improvement over a known low frequency decomposition (the spectral decomposition) is presented. Among other techniques, the well-known Beltrami decomposition of electromagnetic fields is shown to significantly reduce the computational burden in this scheme. Secondly, entirely novel ways of decomposing the Green function are developed in both two and three dimensions. These decompositions use evanescent plane waves, so they can handle small boxes. Nevertheless, they have the same convergence characteristics as the propagating plane wave decomposition. Therefore, these decompositions are also very efficient. Finally, the novel techniques are applied in the full-wave homogenization of various metamaterials

On the Spiral Structure of NGC 2915 and Dark Matter

NGC 2915 is a blue compact dwarf galaxy embedded in an extended, low surface brightness HI disk exhibiting a two-armed spiral structure and a central bar-like component. Commonly accepted mechanisms are unable to explain the existence of these patterns and Bureau et al. proposed disk dark matter (scaling with the HI distribution) or a rotating triaxial dark halo as alternative solutions. In an attempt to explore these mechanisms, hydrodynamical simulations were run for each case and compared to observations using customized column density and kinematic constraints. The spiral structure can be accounted for both by an unseen bar or triaxial halo, the former fitting the observations slightly better. However, the large bar mass or halo pattern frequency required make it unlikely that the spiral wave is driven by an external perturber. In particular, the spin parameter is much higher than predicted by current cold dark matter (CDM) structure formation scenarios. The massive disk models show that when the observed gas surface density is scaled up by a factor about 10, the disk develops a spiral structure resembling closely the observed one, in perturbed density as well as perturbed velocity. This is consistent with more limited studies in other galaxies and suggests that the disk of NGC 2915 contains much more mass than is visible, tightly linked to the neutral hydrogen. A classic (quasi-)spherical halo is nevertheless still required, as increasing the disk mass further to fit the circular velocity curve would make the disk violently unstable. Scaling the observed surface density profile by an order of magnitude brings the disk and halo masses to comparable values within the disk radius.Comment: Accepted for publication in ApJ. Full resolution figures available at http://www.star.qmul.ac.uk/~masset/publications.htm