The present International Celestial Reference Frame (ICRF), the ICRF-3 is based
on a catalogue of 4536 quasar positions obtained from Very Long Baseline Interferometry
(VLBI) radio measurements. This radio frame is crucial for many applications, from
measurements of Earth’s orientation in space to spacecraft navigation and measurements
of sea-level rise. However, the deficit in ICRF source density in the South and lack of
dedicated imaging campaigns in the South, to monitor structural changes, remain a big
concern. These ICRF sources can exhibit spatially extended emission structures that can
have a significant effect on astrometric VLBI measurements. The Celestial Reference
Frame Deep South (CRDS) is a dedicated astrometric VLBI programme to observe
Southern ICRF sources on a regular basis. In an effort to improve the situation in the
South, these CRDS sessions have recently been optimized for VLBI imaging. In this
thesis, I present VLBI images and source structure analysis results for southern ICRF
sources observed in four of these CRDS sessions. For some of these sources, I present
the very first high-resolution radio images. I also present results from source structure
analysis and a corresponding assessment of astrometric quality, and I also present results
from efforts to increase the ICRF source density in the South.Mathematical SciencesPh. D. (Astronomy
