<p>We investigate the clustering of HI-selected galaxies in the ALFALFA survey and compare results with those obtained for HIPASS. Measurements of the angular correlation function and the inferred 3D-clustering are compared with results from direct spatial-correlation measurements. We are able to measure clustering on smaller angular scales and for galaxies with lower HI masses than was previously possible. We calculate the expected clustering of dark matter using the redshift distributions of HIPASS and ALFALFA and show that the ALFALFA sample is somewhat more anti-biased with respect to dark matter than the HIPASS sample. We are able to conform the validity of the dark matter correlation predictions by performing simulations of the non-linear structure formation. Further we examine how the bias evolves with redshift for radio galaxies detected in the the first survey.</p>

For the Swedish Institute of Space Physics and Uppsala University, we have developed a working radio astronomy telescope capable of receiving the 21cm hydrogen line; the Ångström Small Radio Telescope. The work have resulted in a functional system for positioning the dish, with built in tracking of deep space objects and scanning functions, and signal reception with filtering, mixing and digital sampling. The system is controlled via a computer through an Internet connection.

<p>We investigate the clustering of HI-selected galaxies in the ALFALFA survey and compare results with those obtained for HIPASS. Measurements of the angular correlation function and the inferred 3D-clustering are compared with results from direct spatial-correlation measurements. We are able to measure clustering on smaller angular scales and for galaxies with lower HI masses than was previously possible. We calculate the expected clustering of dark matter using the redshift distributions of HIPASS and ALFALFA and show that the ALFALFA sample is somewhat more anti-biased with respect to dark matter than the HIPASS sample. We are able to conform the validity of the dark matter correlation predictions by performing simulations of the non-linear structure formation. Further we examine how the bias evolves with redshift for radio galaxies detected in the the first survey.</p>

Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The Square Kilometre Array (SKA) is an international project to build the world’s largest and most sensitive radio telescope interferometer. It will consist of thousands of antennas distributed over many kilometers, with the hosting country being either South Africa or Australia. Various pathfinders have been initiated to demonstrate the technologies needed to implement the SKA. The astronomy community has defined five Key Science Projects (KSP), which are the drivers for the SKA. The science goals determine the technical requirements needed to design SKA systems. Many years of planning and development are still needed in order to meet to the requirements of such a large and complex project. This thesis aims to present the various SKA pathfinder systems in terms of their application to the SKA key science projects, with main focus that of pulsar observations. In order to achieve this, a thorough overview of basic radio astronomy principles and techniques is presented, followed by a detailed look at the various pathfinders. Throughout the work, aspects of pulsar observations are given particular attention with the goal of designing optimal systems for the SKA. / AFRIKAANSE OPSOMMING: Die Square Kilometre Array (SKA) is ’n internasionale projek om die wêreld se grootste en mees sensitiewe radio teleskoop interferometer te bou. Dit sal bestaan uit duisende antennas versprei oor etlike kilometers, met die gasheer land óf Suid-Afrika óf Australië. Verskeie koersbepalers is geïnisieer om die tegnologie te demonstreer wat benodig is om die SKA te implementeer. Die astronomie gemeenskap het vyf sleutel wetenskap projekte (KSP) gedefinieër wat dien as die drywers vir die SKA. Die wetenskap doelwitte bepaal die tegniese vereistes wat nodig is om SKA stelsels to ontwerp. Talle jare van beplanning en ontwikkeling word steeds benodig om te voldoen aan die vereistes van so ’n groot en komplekse projek. Hierdie tesis het ten doel die aanbieding van verskeie SKA koersbepaler stelsels in terme van hulle aanwending tot die SKA sleutel wetenskap projekte, met hoof fokus op die van pulsar waarnemings. Om dit te behaal, word ’n deeglike oorsig van basiese radio astronomie beginsels en tegnieke aangebied, gevolg deur ’n gedetailleerde kyk na die verskeie koersbepalers. Regdeur die werk word spesifieke aandag gegee aan aspekte van pulsar waarnemings met die doel om optimale stelsels vir die SKA te ontwerp.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Technical advances in electromagnetics, signal processing and processing power have led to a significant increase in sensitivity and accuracy in radio telescopes. With this increase in sensitivity, radio frequency interference (RFI) has become a much larger problem. The notable growth in wireless communication as well as self generated RFI has further escalated this problem. In order to utilise the full capabilities of modern radio telescopes, RFI mitigation is required on the captured signals. With the enormous data rates of modern radio telescopes, managing RFI has become increasingly difficult, and in order to utilise the full captured radio spectrum, more accurate RFI mitigation strategies will be necessary. The use of different RFI mitigation strategies is studied in the form of online and offline techniques. This includes Spectral Kurtosis, Spectral Flatness and the Var/SumThreshold method. The special case for RFI mitigation in timing pulsars will also be studied. These techniques are well known in the radio astronomy community; here, spectral kurtosis and spectral flatness will be implemented on the raw data as well as the post correlated data. System speed and accuracy will be the deciding factors when testing these methods as possible solutions to this problem. / AFRIKAANSE OPSOMMING: ‘n Toename in die sensitiwiteit van hedendagse radioteleskope kan toegedra word aan die tegniese bevordering in elktromagnetika en seinverwerking. Die toename in sensitiwiteit het egter tot die gevolg dat radiofrekwensiesteuring ‘n groter rol speel in hedendaagse radioteleskope. Die groei in die gebruik van radioverbindings asook die gevolge van self gei¨nduseerde radiofrekwensiesteuring dra ook verder by tot hierdie probleem. Radiofrekwensiesteuring matiging word toegepas op die opgevangde seine, om sodoende gebruik te maak van die volle kapasiteit van moderne radioteleskope. Die bestuur van radiofrekwensiesteuring word bemoeilik deur die groot hoeveelheid intydse data van die radioteleskope. Meer akurate radiofrekwensiesteuring matigingstegnieke word vereis om die bandwydte ten volle te hanteer. Daar word op ‘n aantal verskillende matingstegnieke gefokus. Hierdie tegenieke kan in twee kategorieë verdeel word, naamlik aanlyn- en aflyntegenieke. Onderafdelings van hierdie kategorieë sluit in: spektrale kurtose, spektrale matheid en “Var/SumThreshold”. Daar word ook na ‘n spesiale geval van radiofrekwensiesteuring matiging gekyk, in die opmeeting van tydsberekening-pulsars. Alhoewel hierdie tegnieke bekend is in die radioastronomie gemeenskap, word spektrale kurtose en spektrale matheid egter toegepas op die rou data sowel as postgekorreleerde data. Daar sal op stelsel spoed en akuratheid gefokus word, om vas te stel of hierdie metodes wel moontlike oplossings bied tot die probleem bespreek.

The C-Band All-Sky Survey (C-BASS) is a project to produce an all-sky map in intensity and polarization at a central frequency of 5 GHz with 1 GHz bandwidth and approximately 1 degree resolution. The central frequency is low enough for the map to be dominated by synchrotron and free-free emission but high enough so that Faraday rotation and depolarization are small across most of the sky. The C-BASS map will enable a more accurate removal of contaminating foregrounds from measurements of the cosmic microwave background, particularly in polarization where the B-mode signal from inflation is likely to be orders of magnitude weaker than the diffuse Galactic foreground emission. To produce an all-sky map from the ground requires two telescopes, one in the northern and one in the southern hemisphere. This thesis focuses on analysis of C-BASS North data. The noise properties of time-ordered data are characterised by fitting a noise model to periodograms. Using simulations, the errors introduced into the C-BASS maps by a destriping mapmaker are quantified and we reduce the signal error by masking the brightest pixels during baseline offset estimation. Jackknife tests are used to test the C-BASS data for systematics and to test the accuracy of the sensitivity maps. In total intensity, the spectral index of diffuse Galactic emission between 5 GHz and 408 MHz is measured using an extended T-T plot method and the results are compared to simulations. The spectral index of polarized diffuse Galactic emission between 5 GHz and 30 GHz is estimated in 55 arcminute pixels, modelling the polarized intensity as a Rician random variable.

Polarised synchrotron emission from the Milky Way is of interest for its role as a foreground to the polarised CMB and as a probe of the interstellar medium. The Galactic ALFA Continuum Transit Survey (GALFACTS) and the Global Magneto-Ionic Medium Survey (GMIMS) are two ongoing surveys of the diffuse polarised emission around 1.4 GHz, with wide bandwidths and high frequency-resolution. In this thesis, I use early data from GALFACTS to investigate the behaviour of polarised, diffuse Galactic synchrotron emission. I also analyse GMIMS total intensity data. I derive a rotation measure (RM) map of the GALFACTS sky using a combination of RM-synthesis and linear angle fitting, commenting on the structure of the maps in general and on specific regions in particular. Overall I find that the maps are rich in features, and probe the RM structure of the extended Galactic emission with reasonable accuracy. I also derive the Angular Power Spectrum (APS) of the polarised emission for thirty-one 15 by 15 degree subregions across the GALFACTS data. I compute the E- and B-modes (E+B) and the scalar APS of the polarised emission (PI). I parametrise the APS by fitting a power law to the data. Comparing the E+B APS to the PI APS shows that E+B is consistently steeper across the sky. The APS data is also used to estimate the level of foreground contamination of the CMB B-mode by the synchrotron emission. I find that the slope of the APS averaged over high-latitude, low-emission subregions agrees exactly with that of the Planck 30 GHz polarised emission, thus setting an upper limit to the synchrotron contamination of CMB B-modes. Finally, I evaluate the spurious, systematic, temperature zero-level offset and associated uncertainty in preliminary GMIMS total intensity maps, finding a lower limit of ±0.26 K. I also make spectral index maps made using the GMIMS data and the Haslam et al. (1982) 408 MHz map, improving upon previous spectral index maps in the literature.

Un Convertisseur Analogique-Numérique (CAN) pour les applications spatiales en astrophysique et cosmologie a été développé au cours de cette thèse. Cette catégorie de circuits demande des bandes passantes très larges, de très hautes fréquences d'échantillonnage et une faible résolution. L’architecture flash a été retenue pour sa rapidité et sa bande passante. La fréquence d’échantillonnage est de 8GHz. La technologie utilisée est la CMOS 65 nm de chez STMicroeletronics. La conception a été faite en deux phases. Une première qui a amené à un prototype d'un échantillonneur-bloqueur et une deuxième qui a amené au CAN. Les deux prototypes ont été caractérisés et à partir de ces résultats des perspectives d'amélioration pour les nouvelles implémentations ont été retrouvées.Pour atteindre l'objectif final du CAN multi-bits (6-bit sont visés) il a été décidé de dessiner une première version du CAN avec la moitié de la résolution initialement prévue (on passe de 6-bit à 3-bit). L'objectif est de nous permettre d’analyser le comportement des blocs fonctionnels intégrés et ensuite passer à une deuxième voire troisième version pour remplir le cahier des charges initial. / An Analog-to-Digital Converter (ADC) has been developed for astrophysical and cosmological applications. This class of circuits demands, especially in the millimeter wavelength domain, ultra wide bandwidths, ultra high sampling frequencies and a low resolution. The “flash” architecture has been chosen for its speed and bandwidth. This ADC samples at 8Gsps and it has been fabricated in 65nm CMOS technology from STMicroelectornics.The design has been done in two steps. The first was the prototype of a track-and-hold circuit. The second was the ADC. Both circuits have been characterized and from these results some perspectives for further improvements have been proposed.In order to achieve the final goal of the multi-bit ADC (6-bit resolution) we have decided to design a first prototype with half the final resolution, namely a 3-bit resolution ADC. Our idea was, with this first prototype, to conduct a first analysis of the behavior of the integrated functional blocks and, consequently, find the correct improvements required for the ADC final version.

The study of continuum sky background spectrum at low radio frequencies has achieved specific importance in present day observational cosmology . At these low frequencies the sky continuum is contributed by the extragalactic radio sources together with the synchrotron emission of the Milky Way as well as CMB. Following the recombination, the energy exchange between the primordial neutral hydrogen and CMB photons, during its propagation through the ”Dark ages” as well as the ”cosmic dawn” resulted in absorption and emission features in CMB spectrum which evolved with the evolution of the HI over cosmic time. Due to cosmological expansion of the Universe such spectral signatures of cosmological origin is now redshifted to low radio wavelengths. Although the peak to peak amplitudes of the same are smaller by orders of magnitude than the total galactic and extragalactic contribution at these frequencies the later is expected to be smooth over the scales of few hundred MHz. Hence, except for the extreme cases where the time scale over which such radiative transfer interaction occurred is very long and therefore the spectral fluctuations are spread over a large range of frequencies, these cosmological radiation signatures should be detectable at meter wavelengths. The duration and frequency at which such spectral signatures may occur can give constraints on the physical processes that governed the process of such energy exchange at a very early time, the history of evolution of the gas and the nature and evolution of sources of first light in the Universe. Measurements of the absolute brightness of the continuum background at meter wavelengths and detection of the spatial and spectral variations can therefore be an important probe of cosmology. In addition, measurements to date suggest that the radio background that is of extragalactic origin consists of CMB plus a power-law spectrum and has a brightness temperature of (1.2 ± 0.09) × (ν/1 GHz)−2.60±0.04 K. Surprisingly, the sky brightness corresponding to discrete radio sources detected in the deepest surveys to date account for only a fraction of the extragalactic radio background, even after excluding the CMB. Improved measurements of the radio background and, in particular, the spectrum at long wavelengths where errors are relatively larger, are important in estimating the spectrum of the unexplained part and thereby constraining the sources of this cosmic radiation. The wideband measurements at meter wavelengths pose limit on the accuracy of such measurements where the errors are relatively large. The instrument systematics, which are frequency dependent, in interaction with the sky signal may result in an incorrect estimate of the absolute sky brightness as well as may give rise to spectral features which may confuse with the true cosmological signatures in the foreground. A strategic system design with the aim of minimizing the systematics and characterization of the system non-ideal behavior can lead to the measurement accuracy with which the cosmological signatures could be detected along with the absolute measurement of the foreground. The aim of the work that constitute this thesis is precision measurement of the continuum radio emission at long wavelengths and detect the signature from the epoch of reionization in the background spectrum. A single element radio telescope system has been designed and built which is capable of useful measurement of spectral signatures of the EoR in the radio background. SARAS deployed in the Gauribidanur Observatory, about 80 km north of Bangalore in India. The design, calibration method and observation strategies developed are novel and unique, and relevant for any wideband measurements. The content of this thesis is outlined below. The Chapter 1 briefly introduces to the 21 cm cosmology. The neutral hydrogen as an cosmological probe is discussed first. The redshifted 21 cm signal and its possible use to probe the early Universe is discussed in detail. The chapter also gives a description of the redshifted 21 cm background and the EoR global signature as well as the 21 cm power spectrum. Finally an account of the recent and future experiments for detection of the global EoR signature and the EoR power spectrum are given. In the light of the science introduced in this chapter, the major aim and the work of the thesis is also summarised. In Chapter 2 the design philosophy of the SARAS spectrometer is illustrated. The basic elements of the system, the antenna, analog and the digital receiver have been described in detail. The complete configuration and the complex performance of the integrated system are detailed. For an ideal performance of such a wideband system the calibration strategies are considered and measurement equations are derived. Chapter3 addresses the most important issues of systematic effect for this wideband continuum measurement. The designed system performance deviates from its ideal due to non-idealities. The non-ideal behaviour of the real systems that are the limiting factors for a precision wideband measurement at low frequencies are thoroughly investigated. The effects of single and multiple reflections that occurs due to impedance mismatch internal to the system and results in spurious response in the measured data are considered. Within the limits of the known systematics, the system has been argued to qualify to be able to measure the EoR spectral signature in the background spectrum. Chapter 4 gives the details of the SARAS observation and description of the measurement that has been done by the SARAS spectrometer from the Gouribidanur Radio Observatory . The detailed understanding of the systematics led to the two strategic observation modes; EoR mode and RB mode, which are also discussed in this chapter. Next, the absolute calibration of the SARAS spectrometer is described following which the interference rejection algorithms, purpose developed for rejection of RFI from the SARAS data are outlined. The measured data is calibrated and the additional calibration product is derived. The data set is then modelled by modelling the sky noise and the systematic effects. In Chapter 5 the methodology of the SARAS data analysis is illustrated along with step by step analysis of the observation made in the RB mode. The model that is derived in chapter 4 is fitted to the measurements and the parameters are estimated by minimising the merit function Chi-square. The minimisation followed the downhill simplex algorithm which is outlined in this chapter. The data analysis strategy relied on the derivation of the initial values of the parameters from the measured data. The data has been fitted in hierarchy and initial guesses for subset of parameters are derived from each step of hierarchical modelling. This method of analysis is strategic and discussed in detail in this chapter. The statistical and systematic error of measurement are discussed next. Finally, the posterior probability distribution of the parameters are calculated by uniformly sampling the parameter space around the best fit values and calculating the Chi-square and the likelihood functions of the parameters. Mariginalizing the computed posterior probability distribution over the system parameters, the error on estimated sky parameter or the confidence region of the sky parameter is estimated. Chapter 6 presents the analysis identical to that presented in the Chapter 5 for the data acquired in the second observing mode, the EoR mode is presented. In this section the detection ability and the limitations of the SARAS observations, made from the Gouribidanur Radio observatory, for a useful detection of the EoR spectral signature is considered. Chapter 7 described a concept of system bandpass calibration using the time domain information that could be obtained from the voltage samples before computing the power spectrum. In the Chapter 3, the spurious periodic correlation, generated due to the internal reflections of the noise voltages is discussed in detail. If a short pulse is injected into the system via the antenna, due to internal reflections, the primary pulse in the output voltage samples would be followed by a series of delayed pulses each of which is generated by subsequent reflections internal to the system. Inspection of such pulses in the time domain could potentially provide with accurate bandpass calibration. A digital hardware is programmed and a nano second pulse generator-accumulator system is built. The performance of this system and table top demonstration of this bandpass calibration concept is presented in this chapter. This pulse injection system is used in a proposed calibration experiment in the Parkes radio telescope. The initial result of the experiment is presented in this chapter. In Chapter 8 the work carried out for this thesis is summarised. The end to end task of carrying out the background measurement by purpose building a single element radio telescope, observing with it and analysis of the data has led to a successful measurement of the background spectrum with an accuracy > 1%. The detailed understanding of the problems associated with the precision measurements and development of the measurement techniques that can overcome such problems has led to significant progress towards a successful detection of the EoR signatures. Some aspects and ideas which are understood to be essentials for such an experiment yet unexplored here due to limited time are listed in this section and the future prospcts of this work is also discussed.

Philosophiae Doctor - PhD / We investigate the clustering of HI-selected galaxies in the ALFALFA survey and compare results with those obtained for HIPASS. Measurements of the angular correlation function and the inferred 3D-clustering are compared with results from direct spatial-correlation measurements. We are able to measure clustering on smaller angular scales and for galaxies with lower HI masses than was previously possible. We calculate the expected clustering of dark matter using the redshift distributions of HIPASS and ALFALFA and show that the ALFALFA sample is somewhat more anti-biased with respect to dark matter than the HIPASS sample. We are able to conform the validity of the dark matter correlation predictions by performing simulations of the non-linear structure formation. Further we examine how the bias evolves with redshift for radio galaxies detected in the the first survey. / South Africa