An Evolutionary Sequence of Young Radio Galaxies
  We have observed the faintest sample of Gigahertz Peaked Spectrum (GPS) and
Compact Steep Spectrum (CSS) sources to date, using the Australia Telescope
Compact Array. We test the hypothesis that GPS and CSS sources are the youngest
radio galaxies, place them into an evolutionary sequence along with a number of
other young Active Galactic Nuclei (AGN) candidates, and search for evidence of
the evolving accretion mode and its relationship to star formation. GPS/CSS
sources have very small radio jets that have been recently launched from the
central Supermassive Black Hole and grow in linear size as they evolve, which
means that the linear size of the jets is an excellent indicator of the
evolutionary stage of the AGN. We use high-resolution radio observations to
determine the linear size of GPS/CSS sources, resolve their jets and observe
their small-scale morphologies. We combine this with other multi-wavelength age
indicators, including the spectral age, colours, optical spectra and Spectral
Energy Distribution of the host galaxy, in an attempt to assemble all age
indicators into a self-consistent model. We observe the most compact sources
with Very Large Baseline Interferometry, which reveals their parsec-scale
structures, giving us a range of source sizes and allowing us to test what
fraction of GPS/CSS sources are young and evolving.
