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Thesis (PhD)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: This thesis is concerned with the measurement of the complex permeability of thin round wires at radio frequencies. This is of interest as such wires are used in various applications, such as absorbing chaff. Iron and nickel alloys are also used for their good tensile properties but have an undesired electromagnetic effect which needs to be characterised. Although little work has been done in this field in recent decades it remains a relevant problem. In this thesis the advantages of accurate wide-band measurements performed by automatic network analysers are applied to the field. The measurement system is a closed coaxial transmission line with a short circuit termination. The centre conductor is the wire of interest. The surface impedance of the wire is related to complex permeability and is measured using low-loss transmission line approximations applied to half-wavelength resonances. The loss associated with complex permeability is separated from conductivity by a D.C. conductivity measurement. A full wave analysis of the coaxial mode was performed and compared to measured values. The maximum error of the propagation constant was found to be 31% at the highest frequencies and was primarily due to length uncertainties. By varying parameters expected error bands around the measured permeability were found. These bands are of the order 1 and demonstrate that the system is sufficiently robust. The measurement of the permeability of two non-magnetic wires was performed and a relative permeability of 1 was found, demonstrating the correct working of the system. A steel wire was measured and compared to measurements found in literature. The permeability dropped as frequency rose as was expected, and an acceptable comparison to other measurements was made as there is no verification standard. Thus a simple measurement system that takes advantage of calibrated automatic network analyser measurements has been developed and demonstrated to work with sufficient accuracy. / AFRIKAANSE OPSOMMING: In hierdie tesis word die meting van die komplekse permeabiliteit van dun ronde drade by radio frekwensies ondersoek. Hierdie drade word in verskeie toepassings gebruik, waaronder dié van absorberende materiale. Nikkel- en ysterallooie word ook vir hul goeie breekkrageienskappe gebruik. In laasgenoemde gevalle moet die ongewenste elektromagnetiese effekte wat voorkom, gekarakteriseer word. Hoewel baie min werk in onlangse dekades gedoen is, bly die meting van die komplekse permeabiliteit 'n relevante probleem. In hierdie tesis word die voordele van akkurate wyeband metings, soos geneem deur 'n outomatiese netwerk analiseerder, toegepas in dié veld. Die meetopstelling is 'n geslote koaksiale transmissielyn, kortgesluit aan een end. Die middel geleier is die draad van belang. Die oppervlak impedansie van die draad is verwant aan die komplekse permeabiliteit, en word gemeet deur die gebruik van lae verlies transmissielyn benaderings, soos toegepas op halfgolf resonante frekwensies. Die verlies wat met die komplekse permeabiliteit geassosieer word, word van die geleidingsvermoë onderskei deur 'n G.S. meting van die geleidingsvermoë. 'n Volgolf analise van die koaksiale mode is uitgevoer en met gemete waardes vergelyk. 'n Maksimum fout van 31% by die hoogste frekwensie is in die voortplantingskonstante gevind. Hierdie volg primêr uit onsekerhede in lengte. Deur die parameters te varieer kon 'n verwagte foutband rondom die gemete permeabiliteit gevind word. Hierdie bande is van die orde 1 waaruit volg dat die stelsel 'n genoegsame robuustheid toon. Die komplekse permeabiliteit van twee nie-magnetiese drade is gemeet en 'n relatiewe permeabiliteit van 1 is gevind. Hierdie bevestig die korrekte werking van die stelsel. 'n Staal draad is opgemeet en met gepubliseerde meetresultate vergelyk. Soos verwag, verminder die permeabiliteit met 'n verhoging in frekwensie. Hoewel geen verifiëringstandaard beskikbaar is nie, is 'n aanvaarbare vergelyking met ander metings gemaak. Die produk van die navorsing is 'n metingstelsel wat, met behulp van 'n gekalibreerde outomatiese netwerk analiseerder, aanvaarbare akkuraatheid in die meting van die komplekse permeabiliteit van dun ronde drade by radio frekwensies kan verkry.

We present spectral line mapping observations towards four massive star-forming regions Cepheus A, DR21S, S76E and G34.26+0.15 - with the IRAM 30-m telescope at the 2 and 3 mm bands. In total, 396 spectral lines from 51 molecules, one helium recombination line, 10 hydrogen recombination lines and 16 unidentified lines were detected in these four sources. An emission line of nitrosyl cyanide (ONCN, 14(0), 14-13(0), (13)) was detected in G34.26+0.15, as the first detection in massive star-forming regions. We found that c-C3H2 and NH2D show enhancement in shocked regions, as suggested by the evidence of SiO and/or SO emission. The column density and rotational temperature of CH3CN were estimated with the rotational diagram method for all four sources. Isotope abundance ratios of C-12/C-13 were derived using HC3N and its C-13 isotopologue, which were around 40 in all four massive star-forming regions and slightly lower than the local interstellar value (similar to 65). The N-14/N-15 and O-16/O-18 abundance ratios in these sources were also derived using the double isotopic method, which were slightly lower than in the local interstellar medium. Except for Cep A, the S-33/S-34 ratios in the other three targets were derived, which were similar to that in the local interstellar medium. The column density ratios of N(DCN)/N(HCN) and N( DCO+)/N(HCO+) in these sources were more than two orders of magnitude higher than the elemental [D]/[H] ratio, which is 1.5 x 10(-5). Our results show that the later stage sources, G34.26+0.15 in particular, present more molecular species than earlier stage sources. Evidence of shock activity is seen in all stages studied.

We report a discovery of shocked gas from the supernova remnant (SNR) G357.7+0.3. Our millimeter and submillimeter observations reveal broad molecular lines of CO(2-1), CO(3-2), CO(4-3), (CO)-C-13 (2-1), and (CO)-C-13 (3-2), HCO+, and HCN using the Heinrich Hertz Submillimeter Telescope, the Arizona 12 m Telescope, APEX, and the MOPRA Telescope. The widths of the broad lines are 15-30 km s(-1), and the detection of such broad lines is unambiguous, dynamic evidence showing that the SNR G357.7+0.3 is interacting with molecular clouds. The broad lines appear in extended regions (>4'.5 x 5'). We also present the detection of shocked H-2 emission in the mid-infrared but lacking ionic lines using Spitzer/IRS observations to map a few-arcminute area. The H2 excitation diagram shows a best fit with a two-temperature local thermal equilibrium model with the temperatures of similar to 200 and 660 K. We observed [C II] at 158 mu m and high-J CO(11-10) with the German Receiver for Astronomy at Terahertz Frequencies (GREAT) on the Stratospheric Observatory for Infrared Astronomy. The GREAT spectrum of [C II], a 3 sigma detection, shows a broad line profile with a width of 15.7 km(-1) that is similar to those of broad CO molecular lines. The line width of [C II] implies that ionic lines can come from a low-velocity C-shock. Comparison of H2 emission with shock models shows that a combination of two C-shock models is favored over a combination of C- and J-shocks or a single shock. We estimate the CO density, column density, and temperature using a RADEX model. The best-fit model with n(H-2) = 1.7 x 10(4) cm(-3), N(CO) = 5.6 x 10(16) cm(-2), and T = 75 K can reproduce the observed millimeter CO brightnesses.

Doctor of Philosophy (PhD) / This thesis presents the development of new techniques for measuring the mean redshifted 21 cm line of neutral hydrogen during reionization. This is called the 21 cm cosmological reionization monopole. Successful observations could identify the nature of the first stars and test theories of galaxy and large-scale structure formation. The goal was to specify, construct and calibrate a portable radio telescope to measure the 21 cm monopole in the frequency range 114 MHz to 228 MHz, which corresponds to the redshift range 11.5 > z > 5.2. The chosen approach combined a frequency independent antenna with a digital correlation spectrometer to form a correlation radiometer. The system was calibrated against injected noise and against a modelled galactic foreground. Components were specified for calibration of the sky spectrum to 1 mK/MHz relative accuracy. Comparing simulated and measured spectra showed that bandpass calibration is limited to 11 K, that is 1% of the foreground emission, due to larger than expected frequency dependence of the antenna pattern. Overall calibration, including additive contributions from the system and the radio foreground, is limited to 60 K. This is 160 times larger than the maximum possible monopole amplitude at redshift eight. Future work will refine and extend the system known as the Cosmological Reionization Experiment Mark I (CoRE Mk I).

Using various molecular line and continuum emission criteria, we have selected a sample of six isolated, dense concentrations of molecular gas, i.e., “cores”, which are either starless (L694-2, L429, L1517B, and L1689-SMM16) or contain a protostellar Very Low Luminosity Object (VeLLO) and are currently experiencing gravitational collapse (L1014 and L1521F). Studying the molecular emission from dense gas tracers toward this sample of cores will help us gain a more detailed image of the internal physical conditions of dense cores and their evolution. We observed the cores in our sample in NH3 (1,1) and (2,2) emission using the Green Bank Telescope (GBT) and in N2H+ (1−0) emission using the Nobeyama Radio Observatory (NRO). L429 shows the most complicated structure among the cores in our sample. Also, the maxima of molecular line integrated intensities and dust continuum emission toward L429 show a significant offset. The rest of the cores in our sample are roughly round and the morphologies of line integrated intensities follow that of the corresponding continuum emission closely. Cores in our sample have gas kinetic temperatures ∼ 9 − 10 K and therefore show comparable thermal velocity dispersions. L429 and L1517B are, respectively, the most turbulent and most quiescent cores in our sample. Finally, L1521F is the most centrally concentrated core of our sample. L1689-SMM16 is the least previously studied core in our sample and had not yet been probed in molecular emission. Jeans and virial analyses made using updated measurements of core mass and size confirm that L1689-SMM16 is prestellar, i.e., gravitationally bound. It also has accumulated more mass compared to its corresponding Jeans mass in the absence of magnetic fields and therefore is a “super-Jeans” core. The high levels of X(NH3)/X(N2H+) and deuterium fractionation reinforce the idea that the core has not yet formed a protostar. Comparing the physical parameters of the core with those of a Bonnor-Ebert sphere reveals the advanced evolutionary stage of L1689-SMM16 and shows that it might be unstable to collapse. We do not detect any evidence of infall motions toward the core, however. Instead, red asymmetry in the line profiles of HCN (1−0) and HNC (1−0) indicates expansion of the outer layers of the core at a speed of ∼ 0.2 − 0.3 km s−1. For a gravitationally bound core, expansion in the outer layers might indicate that L1689-SMM16 is experiencing oscillations. Radiative transfer modelling of NH3 emission toward L694-2 and L1521F at low and high spatial resolutions show that the less evolved core, L694-2, is best described by relatively constant radial profiles of temperature and fractional NH3 abundance. On the other hand, L1521F, which contains a protostellar VeLLO, is best described by a radial abundance profile that is enhanced toward the core centre and a radial temperature profile that decreases toward the core centre. Comparison of our results with previous studies on L1544, a well-studied starless core, imply that as dense cores evolve and progress toward the moment of collapse, they become more centrally concentrated. As a result, the gas temperatures at their centres decrease, leading to increase in levels of CO depletion factor and increase in NH3 fractional abundance toward the centre. / Graduate

Doctor of Philosophy (PhD) / This thesis presents the development of new techniques for measuring the mean redshifted 21 cm line of neutral hydrogen during reionization. This is called the 21 cm cosmological reionization monopole. Successful observations could identify the nature of the first stars and test theories of galaxy and large-scale structure formation. The goal was to specify, construct and calibrate a portable radio telescope to measure the 21 cm monopole in the frequency range 114 MHz to 228 MHz, which corresponds to the redshift range 11.5 > z > 5.2. The chosen approach combined a frequency independent antenna with a digital correlation spectrometer to form a correlation radiometer. The system was calibrated against injected noise and against a modelled galactic foreground. Components were specified for calibration of the sky spectrum to 1 mK/MHz relative accuracy. Comparing simulated and measured spectra showed that bandpass calibration is limited to 11 K, that is 1% of the foreground emission, due to larger than expected frequency dependence of the antenna pattern. Overall calibration, including additive contributions from the system and the radio foreground, is limited to 60 K. This is 160 times larger than the maximum possible monopole amplitude at redshift eight. Future work will refine and extend the system known as the Cosmological Reionization Experiment Mark I (CoRE Mk I).

We present new Atacama Large Millimeter/submillimeter Array (ALMA) observations of the dust continuum and [C II] 158 mu m fine structure line emission toward a far-infrared-luminous quasar, ULAS J131911.29+095051.4 at z = 6.13, and combine the new Cycle 1 data with ALMA Cycle 0 data. The combined data have an angular resolution of similar to 0.'' 3, and resolve both the dust continuum and the [C II] line emission on a few kiloparsec scales. The [C II] line emission is more irregular than that of the dust continuum emission, which suggests different distributions between the dust and the [C II] emitting gas. The combined data confirm the [C II] velocity gradient that we had previously detected in a lower-resolution ALMA image from the Cycle 0 data alone. We apply a tilted ring model to the [C II] velocity map to obtain a rotation curve, and constrain the circular velocity to be 427 +/- 55 kms(-1) at a radius of 3.2 kpc with an inclination angle of 34 degrees. We measure the dynamical mass within the 3.2 kpc region to be 13.4(-5.3)(+7.8) x 10(10) M-circle dot. This yields a black-hole and host galaxy mass ratio of 0.020(-0.007)(+0.013), which is about 4(-2)(+3) times higher than that of the present-day M-BH/M-bulge ratio. This suggests that the supermassive black hole grows the bulk of its mass before the formation of most of the stellar mass in this quasar host galaxy in the early universe.

We present CI(2-1) and multi-transition (CO)-C-12 observations of a dusty star-forming galaxy, ACT J2029+0120, which we spectroscopically confirm to lie at z = 2.64. We detect CO(3-2), CO(5-4), CO(7-6), CO(8-7), and CI (2-1) at high significance, tentatively detect HCO+(4-3), and place strong upper limits on the integrated strength of dense gas tracers (HCN(4-3) and CS(7-6)). Multi-transition CO observations and dense gas tracers can provide valuable constraints on the molecular gas content and excitation conditions in high-redshift galaxies. We therefore use this unique data set to construct a CO spectral line energy distribution (SLED) of the source, which is most consistent with that of a ULIRG/Seyfert or QSO host object in the taxonomy of the Herschel Comprehensive ULIRG Emission Survey. We employ RADEX models to fit the peak of the CO SLED, inferring a temperature of T similar to 117 K and n(H2) similar to 10(5) cm(-3), most consistent with a ULIRG/QSO object and the presence of high-density tracers. We also find that the velocity width of the C I line is potentially larger than seen in all CO transitions for this object, and that the L'(Ci(2-1))/L'(CO(3-2)) ratio is also larger than seen in other lensed and unlensed submillimeter galaxies and QSO hosts; if confirmed, this anomaly could be an effect of differential lensing of a shocked molecular outflow.

Recombination line profile shapes are derived for ionized spherical stellar winds at radio wavelengths. It is assumed that the wind is optically thick owing to free-free opacity. Emission lines of arbitrary optical depth are obtained assuming that the free-free photosphere forms in the outer, constant expansion portion of the wind. Previous works have derived analytic results for isothermal winds when the line and continuum source functions are equal. Here, semi-analytic results are derived for unequal source functions to reveal that line shapes can be asymmetric about line center. A parameter study is presented and applications discussed.