A transformation used to obtain solutions for the beam parameter equation of fiber optics is applied to the second order differential equation for nonuniform transmission lines. Methods are developed for deriving possible transmission line tapers from known solutions of the transformed equation. This study begins with a comprehensive overview of previous work done to obtain closed-form solutions for the transmission line equations. Limitations of the lumped parameter model are also discussed. As part of this thesis, a tapered transmission line is constructed, based on one of the solutions obtained from the fiber optics studies. A discussion of the design and measurement results are given in the final chapter.

A sample of 9 small-diameter radio sources has been selected from the Molonglo Galactic Plane Survey (MGPS) and observed with the Australia Telescope Compact Array (ATCA) in the radio recombination line (RRL) at 5 GHz, in a search for young Galactic SNRs. Since the RRL emission is an unambiguous indicator of a thermal source, this method has been used to eliminate HII regions from the selected sample. In addition, the IRAS and MSX infrared data and spectral index measurements have been combined with the RRL studies to distinguish thermal and non-thermal sources in the selected sample. One source (G282.8-1.2) is identified here as a possible new young Galactic supernova remnant, based on its relatively weak infrared emission, steep radio spectrum and possible x-ray emission. However, the ATCA data are inconclusive and further studies are needed to confirm this result. Radio recombination line emission (H107 alpha) has been detected in 3 of the selected sources, eliminating them from the sample of SNR candidates. In addition, the parameters of the RRL emission from the identified HII regions have been used to estimate their properties. The RRL data are inconclusive for the remaining low brightness, extended sources in the sample. However, some of these sources are likely to be thermal HII regions according to the infrared and spectral index data. The selected method for distinguishing thermal and non-thermal Galactic radio sources seems promising. The selected ATCA configuration was appropriate for imaging relatively bright, compact sources, but a slightly modified observing technique is needed to successfully image low surface brightness, extended sources.

A sample of 9 small-diameter radio sources has been selected from the Molonglo Galactic Plane Survey (MGPS) and observed with the Australia Telescope Compact Array (ATCA) in the radio recombination line (RRL) at 5 GHz, in a search for young Galactic SNRs. Since the RRL emission is an unambiguous indicator of a thermal source, this method has been used to eliminate HII regions from the selected sample. In addition, the IRAS and MSX infrared data and spectral index measurements have been combined with the RRL studies to distinguish thermal and non-thermal sources in the selected sample. One source (G282.8-1.2) is identified here as a possible new young Galactic supernova remnant, based on its relatively weak infrared emission, steep radio spectrum and possible x-ray emission. However, the ATCA data are inconclusive and further studies are needed to confirm this result. Radio recombination line emission (H107 alpha) has been detected in 3 of the selected sources, eliminating them from the sample of SNR candidates. In addition, the parameters of the RRL emission from the identified HII regions have been used to estimate their properties. The RRL data are inconclusive for the remaining low brightness, extended sources in the sample. However, some of these sources are likely to be thermal HII regions according to the infrared and spectral index data. The selected method for distinguishing thermal and non-thermal Galactic radio sources seems promising. The selected ATCA configuration was appropriate for imaging relatively bright, compact sources, but a slightly modified observing technique is needed to successfully image low surface brightness, extended sources.

The gas kinetic temperature (T-K) of various interstellar environments is often inferred from observations that can deduce level populations of atoms, ions, or molecules using spectral line observations; H I 21 cm is perhaps the most widely used, and has a long history. Usually the H I 21 cm line is assumed to be in thermal equilibrium. and the populations are given by the Boltzmann distribution. A variety of processes, many involving Ly alpha, can affect the 21 cm line. Here we show how this is treated in the spectral simulation code Cloudy, and present numerical simulations of environments where this temperature indicator is used, with a detailed treatment of the physical processes that determine level populations within H-0. We discuss situations where this temperature indicator traces TK, cases where it fails, as well as the effects of Lya pumping on the 21 cm spin temperature. We also show that the Lya excitation temperature rarely traces the gas kinetic temperature.

We report new ALMA observations of the CO(3-2) line emission from the 2.1 +/- 0.3*10(10)M(circle dot). molecular gas reservoir in the central galaxy of the Phoenix cluster. The cold molecular gas is fueling a vigorous starburst at a rate of 500-800M(circle dot)yr(-1) and powerful black hole activity in the forms of both intense quasar radiation and radio jets. The radio jets have inflated huge bubbles filled with relativistic plasma into the hot, X-ray atmospheres surrounding the host galaxy. The ALMA observations show that extended filaments of molecular gas, each 10-20 kpc long with a mass of several billion solar masses, are located along the peripheries of the radio bubbles. The smooth velocity gradients and narrow line widths along each filament reveal massive, ordered molecular gas flows around each bubble, which are inconsistent with gravitational free-fall. The molecular clouds have been lifted directly by the radio bubbles, or formed via thermal instabilities induced in low-entropy gas lifted in the updraft of the bubbles. These new data provide compelling evidence for close coupling between the radio bubbles and the cold gas, which is essential to explain the self-regulation of feedback. The very feedback mechanism that heats hot atmospheres and suppresses star formation may also paradoxically stimulate production of the cold gas required to sustain feedback in massive galaxies.

We report the second complete molecular line data release from the Census of High-and Medium-mass Protostars (CHaMP), a large-scale, unbiased, uniform mapping survey at sub-parsec resolution, of millimeter-wave line emission from 303 massive, dense molecular clumps in the Milky Way. This release is for all (CO)-C-12 J = 1 -> 0 emission associated with the dense gas, the first from Phase II of the survey, which includes (CO)-C-12, (CO)-C-13, and (CO)-O-18. The observed clump emission traced by both (CO)-C-12 and HCO+ (from Phase I) shows very similar morphology, indicating that, for dense molecular clouds and complexes of all sizes, parsec-scale clumps contain. similar to 75% of the mass, while only 25% of the mass lies in extended (>10 pc) or "low density" components in these same areas. The mass fraction of all gas above a density of 10(9) m(-3) is xi(9) greater than or similar to 50%. This suggests that parsec-scale clumps may be the basic building blocks of the molecular interstellar medium, rather than the standard GMC concept. Using (CO)-C-12 emission, we derive physical properties of these clumps in their entirety, and compare them to properties from HCO+, tracing their denser interiors. We compare the standard X-factor converting I (CO)-C-12 to N-H2 with alternative conversions, and show that only the latter give whole-clump properties that are physically consistent with those of their interiors. We infer that the clump population is systematically closer to virial equilibrium than when considering only their interiors, with perhaps half being long-lived (10s of Myr), pressure-confined entities that only terminally engage in vigorous massive star formation, supporting other evidence along these lines that was previously published.

We present deep NH₃ and CCS maps of L1495-B218 filaments and the dense cores embedded within the filaments in Taurus. The L1495-B218 filaments form an interconnected, nearby, large complex extending over 8 pc. We observed the filaments in NH₃ (1,1)&(2,2), CCS Nⱼ = 1₂-0₁, and HC₇N J = 21-20 with spectral resolution of 0.038 km/s and spatial resolution of 31". The CSAR algorithm, which is a hybrid of seeded-watershed and binary dendrogram algorithm, identifies 39 leaves and 16 branches in NH₃ (1,1). Applying a virial analysis for the 39 NH₃ leaves, we find only 9 out of 39 leaves are gravitationally bound, and 12 out of 30 gravitationally unbound leaves are pressure-confined. Our analysis suggests that a dense core may form as a pressure-confined structure, evolve to a gravitationally bound core, and then undergo collapse to form a protostar. We find that the L1495A, B213E, and B216 regions have strong CCS emission and the B211 and B218 regions have weak CCS emission. Analysis of CCS emission with NH₃ (1,1) and dust continuum emission shows that CCS is not a good tracer for starless core evolution. On the other hand, CCS appears to trace recently accreted gas in L1495A and L1521D. We also present more realistic dynamic stability conditions for dense cores and filaments. In a new analysis of stability conditions we account for converging motions which have been modeled toward starless cores and take the effect of radiation fields. We find that the critical size of a dense core having a homologous converging motion with its peak speed being the sound speed is roughly half of the critical size of the Bonnor-Ebert sphere. We also find the critical mass/line density of a dense core/filament irradiated by radiation to be considerably smaller than that of the Bonnor-Ebert sphere/isothermal cylinder when the radiation pressure is stronger than the central gas pressure of dense core/isothermal cylinder. For regions in the inner Galaxy and near OB associations, the critical mass/line density of a dense structure may be less than 20% of the critical mass/line density of Bonnor-Ebert sphere/isothermal cylinder.

New detections of HNC have been made toward 11 planetary nebulae (PNe), including K4-47, K3-58, K3-17, M3-28, and M4-14. These sources, which represent a wide range of ages and morphologies, had previously been observed in HCN by Schmidt & Ziurys. Measurements of the J = 1 -> 0 and J = 3 -> 2 transitions of HNC near 90 and 271 GHz were conducted using the new 12 m and the Sub-Millimeter Telescope of the Arizona Radio Observatory. HCN and HNC were also identified via their J = 1 -> 0 lines toward eight positions across the Helix Nebula (NGC 7293). Column densities for HNC, determined from radiative transfer modeling, were N-tot(HNC) similar to (0.06-4.0) x 10(13) cm(-2), corresponding to fractional abundances with respect to H-2 of f similar to (0.02-1.4) x 10(-7). The HCN and HNC column densities across the Helix were found to be N-tot (HCN) similar to (0.2-2.4). x. 10(12) cm(-2) and Ntot (HNC) similar to (0.07-1.6). x. 1012 cm(-2), with fractional abundances of (0.2-3.2) x 10(-7) and (0.09-2.2) x 10(-7). The [ HCN]/[ HNC] ratio varied between similar to 1-8 for all PNe, with [ HCN]/[ HNC] similar to 1-4 across the Helix. These values are greatly reduced from what has been found in asymptotic giant branch stars, where the ratio is typically > 100. Both the abundance of HNC and the [ HCN]/[ HNC] ratio do not appear to vary significantly with nebular age across a time span of similar to 10,000 years, in contrast to predictions of chemical models. The increase in HNC appears to arise in the proto-planetary stage, but becomes " frozen" once the PN phase is reached.

New detections of CCH have been made toward nine planetary nebulae (PNe), including K4-47, K3-58, K3-17, M3-28, and M4-14. Measurements of the N = 1 -> 0 and N = 3 -> 2 transitions of this radical near 87 and 262 GHz were carried out using the new 12 m and the Sub-Millimeter Telescope (SMT) of the Arizona Radio Observatory (ARO). The presence of fine and/or hyperfine structure in the spectra aided in the identification. CCH was not observed in two PNe which are sources of C-60. The planetary nebulae with positive detections represent a wide range of ages and morphologies, and all had previously been observed in HCN and HNC. Column densities for CCH in the PNe, determined from radiative transfer modeling, were N-tot(CCH) similar to 0.2-3.3 x 10(15) cm(-2), corresponding to fractional abundances with respect to H-2 of f similar to 0.2-47 x 10(-7). The abundance of CCH was found to not vary significantly with kinematic age across a time span of similar to 10,000 years, in contrast to predictions of chemical models. CCH appears to be a fairly common constituent of PNe that are carbon-rich, and its distribution may anti-correlate with that of C-60. These results suggest that CCH may be a product of C-60 photodestruction, which is known to create C-2 units. The molecule may subsequently survive the PN stage and populate diffuse clouds. The distinct, double-horned line profiles for CCH observed in K3-45 and M3-28 indicate the possible presence of a bipolar flow oriented at least partially toward the line of sight.

The astronomical size of spectral data cubes that will result from the SKA pathfinders planned large HI surveys such as LADUMA; Fornax HI survey; DINGO; WALLABY; etc. necessitate fully automated three-dimensional (3D) source finding and parametrization tools. A fraction of the percentage difference in the performance of these automated tools corresponds to a significant number of galaxies being detected or undetected. Failure or success to resolve satellites around big spirals will affect both the low and the high mass end of the HI mass function. As a result, the performance and efficiency of these automated tools are of great importance, especially in the epoch of big data. Here I present the comprehensive comparison of performance between the fully automated source identification and parametrization software: SOFIA, the visual galaxy identification method and the semi-automated galaxy identification method. Each galaxy identification method has been applied to the same ∼ 35 gigabytes 3D HI data cube. The data cube results from the blind HI imaging survey conducted using the Westerbork Synthesis Radio Telescope (WSRT). The survey mapped the overdensity corresponding to the Perseus-Pisces Supercluster filament crossing the Zone-of-Avoidance (ZoA), at (`, b) ≈ (160◦ , 0.5◦ ). A total of 211 galaxies detected using the semi-automated method by Ramatsoku et al. [2016]. In this work, I detected 194 galaxies (using the visual identification method) of which 89.7% (174) have cross-matches/counterparts on the galaxy catalogue produced through semi-automated identification method. A total of 130 detections were made using SOFIA of which 89 were also identified by the two other methods. I used the sample of 174 visual detections with semi-automated counterparts as a Testbed to calculate the reliability and completeness achieved by SOFIA. The achieved reliability is ∼ 0.68 whereas completeness is ∼ 0.51. Further parameter fine-tuning is necessary to have a better handle on all SOFIA parameters and achieve higher reliability and completeness values.